J/Psi Preprints
QCD coherence effects in high energy reactions with nuclei
J. Raufeisen
In this work, coherence effects in deep inelastic scattering (DIS) and in the
Drell-Yan (DY) process off nuclei are investigated, in particular nuclear
shadowing. The target rest frame and the color dipole formulation are employed.
Multiple scatterings are treated in Glauber-Gribov theory, which is modified to
include the nuclear form factor to all orders. Based on the mean coherence
length, which is defined in this work, it is estimated that gluon shadowing is
negligible at x_{Bj}>0.01. Parameter free calculations are compared to NMC and
E665 data for DIS and to E772 data for DY. In both cases, good agreement is
found. It is however not possible to reproduce the effect observed by HERMES.
For dileptons in proton-nucleus collisions at RHIC energies, considerable
shadowing for the whole x_F range is predicted. The influence of the nucleus on
the DY transverse momentum distribution is also studied. Furthermore, a new
parametrization of the dipole cross section is presented.
SPIRES or
http://arXiv.org/abs/hep-ph/0009358
QCD Radiation off Heavy Particles
E. Norrbin and T. Sj\"ostrand
We study QCD radiation in decay processes involving heavy particles. As
input, the first-order gluon emission rate is calculated in a number of
reactions, and comparisons of the energy flow patterns show a non-negligible
process dependence. To proceed further, the QCD parton shower language offers a
convenient approach to include multi-gluon emission effects, and to describe
exclusive event properties. An existing shower algorithm is extended to take
into account the process-dependent mass, spin and parity effects, as given by
the matrix element calculations. This allows an improved description of
multiple gluon emission effects off b and t quarks, and also off nonstandard
particles like squarks and gluinos. Phenomenological applications are presented
for bottom production at LEP, Higgs particle decay to heavy flavours, top
production and decay at linear colliders, and some simple supersymmetric
processes.
SPIRES or
http://arXiv.org/abs/hep-ph/0010012
The charmed and bottom meson spectrum from lattice NRQCD
Randy Lewis and R. M. Woloshyn
The mass spectrum of S and P-wave mesons containing a single heavy quark has
been computed using quenched lattice nonrelativistic QCD. Numerical results
have been obtained at first, second and third order in the heavy quark
expansion, so convergence can be discussed. The computed spectrum of charmed
and bottom mesons is compared to existing model calculations and experimental
data.
SPIRES or
http://arXiv.org/abs/hep-ph/0010013
Equation of State in Quantum Chromodynamics
V.I. Yukalov, E.P. Yukalova
The equation of state for quark-gluon plasma is obtained, being valid for
arbitrary values of the coupling parameter and of temperature. This equation is
constructed from perturbative expansions for free energy and for
renormalization function. Summation of asymptotic perturbative series is
accomplished by means of the self-similar approximation theory.
SPIRES or
http://arXiv.org/abs/hep-ph/0010028
Hadronic interactions of the J/psi
Kevin L. Haglin (SCSU) and Charles Gale (McGill)
We calculate the cross sections for reactions of the J/psi with light mesons.
We also evaluate its finite temperature spectral function. We investigate
separately the role of elastic and inelastic channels and we compare their
respective importance. We describe J/psi absorption channels that have not been
considered previously to our knowledge. The relevance of our study to heavy ion
collisions is discussed.
SPIRES or
http://arXiv.org/abs/nucl-th/0010017
SPIRES or
www
Searching Saturation in eA Processes
V. P. Goncalves (IFM - UFPel)
The high density effects should be manifest at small x and/or large nuclei.
In this letter we consider the behavior of nuclear structure function $F_2^A$
slope in the kinematic region which could be explored in the future eA
colliders as a search of these effects. We verify that the high density implies
that the maximum value of the slope occurs at large values of the photon
virtuality, i.e. in a perturbative regime, and is dependent of the number of
nucleons A and energy. Our conclusion is that the measurement of this
observable will allow to explicit the saturation.
SPIRES or
http://arXiv.org/abs/hep-ph/0010060
Multiplicity of different hadrons in e+e-, pp, and AA collisions
H. Drescher, J. Aichelin, and K. Werner
Employing the recently developed neXus model, we compare the yields of
different hadrons in ultra-relativistic collisions: electron-positron
annihilation at 91 GeV, proton-proton scattering at 17 GeV and nucleus-nucleus
collisions at 17 GeV (SPS) and 200 GeV (RHIC). Plotting the yields as a
function of the hadron masses, we find very surprising results: we observe that
the spectra are practically identical for e+e- at 91 GeV and central
nucleus-nucleus reactions at SPS and RHIC energies, whereas the spectrum for
proton-proton scattering is somewhat steeper. All have the form one expects if
the particles were emitted by a canonical system which is characterized by a
temperature and chemical potentials. These identical forms have, however,
different origins: in e+e- and pp the exponential shape it is due to the
statistical behavior of string fragmentation, which has absolutely nothing to
do with thermalization, in AA it is caused by phase space. The fact that e+e-
and nuclear results agree is pure coincidence. Surprisingly the results for pp
and e+e- differ, although here the production mechanism is identical. In pp
collisions we see directly that the string energy is very limited and hence the
high mass baryons are suppressed. We conclude that it is practically impossible
to draw conclusions from hadronic yields about the reaction mechanism.
SPIRES or
http://arXiv.org/abs/hep-ph/0010094
When can long-range charge fluctuations serve as a QGP signal?
E.V. Shuryak and M.A. Stephanov
We critically discuss recent suggestion to use long-range modes of charge
(electric or baryon) fluctuations as a signal for the presence of Quark-Gluon
Plasma at the early stages of a heavy ion collision. We evaluate the rate of
diffusion in rapidity for different secondaries, and argue that for conditions
of the SPS experiments, it is strong enough to relax the magnitude of those
fluctuations almost to its equilibrium values, given by hadronic ``resonance
gas''. We further argue that experimental data from SPS agree with this
conclusion. We evaluate the detector acceptance needed to measure such
``primordial'' long-range fluctuations at RHIC conditions. We conclude with an
application of the charge fluctuation analysis to the search for the QCD
critical point.
SPIRES or
http://arXiv.org/abs/hep-ph/0010100
Probing For New Physics In J/$\Psi$ Decays
X. Zhang (IHEP, Beijing)
Beijing Spectrometer (BES) at Beijing Electron Positron Collider (BEPC), IHEP
has accumulated 2.5 $\times 10^7$ J/$\Psi$ and plans to increase the number to
$10^8 \sim 10^9$ in the near future. In this paper I review and summarize the
recent studies on the possibilities of probing for new physics at BES. This
includes the theoretical works on and experimental attempt performed at BES in
searching for flavor changing neutral current, CP violation and lepton flavor
violation in the processes of J/$\Psi$ decays.
SPIRES or
http://arXiv.org/abs/hep-ph/0010105
QCD sum rule analysis of the charmonium system: The charm quark mass
Markus Eidemuller and Matthias Jamin
In this work, the charm quark mass is obtained from a QCD sum rule analysis
of the charmonium system. In our investigation we include results from
non-relativistic QCD at next-to-next-to-leading order. Using the pole mass
scheme, we obtain a value of $M_c=1.70\pm 0.13$ GeV for the charm pole mass.
The introduction of a potential-subtracted mass leads to an improved scale
dependence. The running ${\rm \MSb}$-mass is then determined to be
$m_{c}(m_{c}) = 1.23 \pm 0.09$ GeV.
SPIRES or
http://arXiv.org/abs/hep-ph/0010133
J/psi and psi(2S) Production and Polarization at the Tevatron
Michael Kr\"amer (University of Edinburgh)
The NRQCD factorization approach for quarkonium production at hadron
colliders is reviewed. The prediction of J/psi and psi(2S) transverse
polarization at large transverse momentum is confronted with recent
experimental data, and potential shortcomings of the theoretical analysis are
discussed.
SPIRES or
http://arXiv.org/abs/hep-ph/0010137
Statistical Coalescence Model with Exact Charm Conservation
M.I. Gorenstein, A.P. Kostyuk, H. Stoecker and W. Greiner
The statistical coalescence model for the production of open and hidden charm
is considered within the canonical ensemble formulation. The data for the J/psi
multiplicity in Pb+Pb collisions at 158 A GeV are used for the model prediction
of the open charm yield which has not yet been measured in these reactions.
SPIRES or
http://arXiv.org/abs/hep-ph/0010148
Quarks in nuclear medium
K. Saito
Using the quark-meson coupling (QMC) model we study nuclear matter from the
point of view of quark degrees of freedom. As the nucleon model we adopt the
MIT bag model and the relativistic constituent quark model, where a square well
and harmonic oscillator potentials are used to confine the quarks. We introduce
the Lorentz-vector type confining potential as well as the Lorentz-scalar type
one in order to examine how the vector confining potential contributes to the
properties of the nucleon and nuclear matter. Next, we perform a re-definition
of the scalar field in matter and transform the QMC model to a QHD-type model
with a non-linear scalar potential. The result obtained from QMC is then
compared with the potentials which are determined so as to fit various
properties of finite nuclei and nuclear matter in relativistic mean-field
models. The QMC model provides the parameters $\kappa \sim 20 - 40$ (fm$^{-1}$)
and $\lambda \sim 80 - 400$ for the standard, non-linear scalar potential. We
discuss a relationship between the QMC and QHD-type models in detail.
SPIRES or
http://arXiv.org/abs/nucl-th/0010035
SPIRES or
www
Coherent particle production in collisions of relativistic nuclei
George L. Gogiberidze (JINR & IUCF), Edward K.G. Sarkisyan (CERN & Tel
Here we give the results of our study of features of dense groups, or spikes,
of particles produced in Mg-Mg and C-Cu collisions at, respectively, 4.3 and
4.5 GeV/c/nucleon aimed to search for a coherent, Cerenkov-like, mechanism of
hadroproduction.
We investigate the distributions of spike centers and, for Mg-Mg interactions,
the energy spectra of negatively charged particles in spikes. The spike-center
distributions are obtained to exhibit the structure expected from coherent
gluon-jet emission dynamics.
This structure is similar in both cases considered, namely for all charged and
negatively charged particles, and is also similar to that observed recently for
all-charged-particle spikes in hadronic interactions. The energy distribution
within spikes is found to have a significant peak over the inclusive
background, while the inclusive spectrum shows exponential decrease with two
characteristic values of average kinetic energy.The value of the peak energy
and its width are in a good agreement with those expected for pions produced in
a nuclear medium in the framework of the Cerenkov quantum approach.
The peak energy obtained is consistent with the value of the cross-section
maximum observed in coincidence nucleon-nucleus interaction experiments.
SPIRES or
http://arXiv.org/abs/hep-ph/0010190
QCD factorization with heavy quarks
German Rodrigo (Karlsruhe U.) and Marcello Ciafaloni (Florence U. &
We further analyze the definition and the calculation of the heavy quark
impact factor at next-to-leading (NL) $\log s$ level, and we provide its
analytical expression in a previously proposed k-factorization scheme. Our
results indicate that k-factorization holds at NL level with a properly chosen
energy scale, and with the same gluonic Green's function previously found in
the massless probe case.
SPIRES or
http://arXiv.org/abs/hep-ph/0010216
Kinematic Effects in Radiative Quarkonia Decays
Stefan Wolf (TTP, U. of Karlsruhe)
Non-relativistic QCD (NRQCD) predicts colour octet contributions to be
significant not only in many production processes of heavy quarkonia but also
in their radiative decays. We investigate the photon energy distributions in
these processes in the endpoint region. There the velocity expansion of NRQCD
breaks down which requires a resummation of an infinite class of colour octet
operators to so-called shape functions. We model these non-perturbative
functions by the emission of a soft gluon cluster in the initial state. We
found that the spectrum in the endpoint region is poorly understood if the
values for the colour octet matrix elements are taken as large as indicated
from NRQCD scaling rules. Therefore the endpoint region should not be taken
into account for a fit of the strong coupling constant at the scale of the
heavy quark mass.
SPIRES or
http://arXiv.org/abs/hep-ph/0010217
J/psi absorption by pi and rho mesons in meson exchange model with anomalous parity interactions
Yongseok Oh, Taesoo Song, Su Houng Lee
We reanalyze the dissociation process of the $J/\psi$ by $\pi$ and $\rho$
mesons into $D + \bar{D}$, $D^* + \bar{D}$, $D + \bar{D}^*$, and $D^* +
\bar{D}^*$ within a meson exchange model. In addition to the dissociation
mechanisms considered in the literature, we consider anomalous parity
interactions, whose couplings are constrained by heavy quark spin symmetry and
phenomenology. This opens new dissociation channels and adds new diagrams in
the previously considered processes. Compared to the previous results, we find
that these new additions have only a minor effect on the $\rho + J/\psi$ total
inelastic cross section, but reduce the one for $\pi + J/\psi$ by about 50 %
near the threshold.
SPIRES or
http://arXiv.org/abs/nucl-th/0010064
Soft Pomeron in QCD
Eugene Levin (Tel Aviv U. /DESY)
This is a talk, given at Diffraction'2000, Sept. 2 - 7, Centraro, Italy. This
talk is a brief presentation of our view on the Pomeron, as a non-perturbative
QCD phenomenon but from sufficiently short distances. Our approach is based on
the scale anomaly of QCD and emphasizes the r{\^o}le of semi-classical QCD
vacuum fields. We show that both the intercept and the slope of Pomeron
trajectory appear to be determined by the energy density of non-perturbative
QCD vacuum. The particular example of semi-classical QCD vacuum fields is
discussed based on a new type of instanton-induced interactions (``instanton
ladder'') that leads to the rising with energy cross section $\sigma \sim
s^{\Delta_P}$ of Regge type (the Pomeron).
SPIRES or
http://arXiv.org/abs/hep-ph/0010271
On the Character of Leading Asymmetry in the Hadroproduction of Charmed Mesons and Baryons
O.I.Piskounova (P.N.Lebedev Physical Institute, Moscow, Russia)
The character of asymmetry between the spectra of Lambda_c and antiLambda_c
in the E781 experiment (FNAL) is discussed on the basis of the Quark Gluon
String Model(QGSM). As it was shown in the description of the asymmetry between
the spectra of leading and nonleading charmed mesons measured in Sigma^--A
interactions at p_L= 340 GeV/c in the WA89 experiment in previous studies, the
asymmetries between D^- and D^+ meson spectra and between D_s^- and D^+_s meson
spectra can be fitted by QGSM curves with the same parameter of string
fragmentation, a_1=10, as well as the asymmetry between the D-meson spectra in
pion-nuclear collisions in the E791 experiment. The forms of
Lambda_c/antiLambda_c asymmetry dependences measured in Sigma^-A and p-A
collisions at p_L= 600 GeV/c in the E781 experiment are different . It is shown
in the framework of QGSM that they depend on whether the diquarks of beam and
target particles took part in charmed baryon formation or not. The QGSM results
are compared with the calculations carried out by the other authors.
SPIRES or
http://arXiv.org/abs/hep-ph/0010263
Energy loss of fast quarks in nuclei
M.B. Johnson, B.Z. Kopeliovich, I.K. Potashnikova, P.L. McGaughey,
We report an analysis of the nuclear dependence of the yield of Drell-Yan
dimuons from the 800 GeV/c proton bombardment of $^2H$, C, Ca, Fe, and W
targets. Employing a new formulation of the Drell-Yan process in the rest frame
of the nucleus, this analysis examines the effect of initial-state energy loss
and shadowing on the nuclear-dependence ratios versus the incident proton's
momentum fraction and dimuon effective mass. The resulting energy loss per unit
path length is $-dE/dz = 2.32 \pm 0.52\pm 0.5$ GeV/fm. This is the first
observation of a nonzero energy loss of partons traveling in nuclear
environment.
SPIRES or
http://arXiv.org/abs/hep-ex/0010051
Excitation of Color Degrees of Freedom of Nuclear Matter and $J/\psi$ Suppression
J\"org H\"ufner, Boris Z. Kopeliovich and Alberto Polleri
In high energy nuclear collisions, the conventional Glauber model is commonly
used to evaluate the contribution to $J/\psi$ suppression originating from the
inelastic interaction with colorless bound nucleons. This requires an effective
value for the $J/\psi$-nucleon absorption cross section which is larger than
theoretically expected. On the other hand, multiple nucleon-nucleon collisions
mediated by color exchange interactions, excite their color degrees of freedom.
We investigate the importance of this effect and find that these excited states
provide a larger cross section for $J/\psi$ absorption. We conclude that the
related corrections are important to explain the effective value extrapolated
from experiment.
SPIRES or
http://arXiv.org/abs/hep-ph/0010282
The Role of Hadronization in Charm and Beauty Production
Yu.M.Shabelski (Petersburg Nuclear Physics Institute, Gatchina,
We discuss the relative role of fragmentation and recombination processes for
heavy flavour hadron production in different kinematical regions in high energy
hadron-hadron and photon-hadron collisions. We predict several qualitative
features which should be observed if our picture of heavy flavour production is
consistent.
SPIRES or
http://arXiv.org/abs/hep-ph/0011032
New Anomalous Exchange in Regge Phenomenology and Hard Diffraction
N.I. Kochelev,D.-P. Min, Y. Oh, V.Vento, A.V. Vinnikov
A new mechanism for hard diffraction based on the anomalous $f_1$ trajectory
exchange, which we identify as the odd signature partner of the Pomeron, is
suggested. We calculate the contribution of the $f_1$ exchange to elastic and
dissociative electromagnetic production of vector mesons and show that it gives
a dominant contribution to the differential cross sections at large momentum
transfers.
SPIRES or
http://arXiv.org/abs/hep-ph/0011042
Massive c(\bar c)g-Production in Diffractive DIS
J. Bartels, H. Jung, A. Kyrieleis
We calculate the cross section for q(\bar q)g-production in diffractive DIS
with finite fermion masses and zero momentum transfer. The calculation is done
in the leading log(1/x_p) approximation and is valid for the region of high
diffractive masses (small beta). We apply our cross section formula to
diffractive charm production at HERA: in a Monte-Carlo-Simulation of
diffractive D*+- meson production we include both massive q(\bar q)- and
massive q(\bar q)g-production, and we compare with preliminary H1 results.
After adjusting an infrared cutoff parameter of our model which affects the
overall normalization of the cross section we find reasonable agreement with
the data. In particular, the slope of the beta-distribution can be reproduced.
SPIRES or
http://arXiv.org/abs/hep-ph/0010300
Photoproduction of charm near threshold
S.J. Brodsky, E. Chudakov, P. Hoyer and J.M. Laget
Charm and bottom production near threshold is sensitive to the multi-quark,
gluonic, and hidden-color correlations of hadronic and nuclear wavefunctions in
QCD since all of the target's constituents must act coherently within the small
interaction volume of the heavy quark production subprocess. Although such
multi-parton subprocess cross sections are suppressed by powers of $1/m^2_Q$,
they have less phase-space suppression and can dominate the contributions of
the leading-twist single-gluon subprocesses in the threshold regime. The small
rates for open and hidden charm photoproduction at threshold call for a
dedicated facility.
SPIRES or
http://arXiv.org/abs/hep-ph/0010343
A simple solution to color confinement
Johan Hansson
We show that color confinement is a direct result of the nonabelian, i.e.
nonlinear, nature of the color interaction in quantum chromodynamics. This
makes it in general impossible to describe the color field as a collection of
elementary quanta (gluons). A quark cannot be an elementary quanta of the quark
field, as the color field of which it is the source is itself a source hence
making isolated (noninteracting) quarks impossible. In geometrical language,
the impossibility of quarks and gluons as physical particles arises due to the
fact that the color Yang-Mills space does not have a constant trivial
curvature.
SPIRES or
http://arXiv.org/abs/hep-ph/0011060
Debye Screening in the QCD plasma
O. Philipsen (CERN and MIT)
Various definitions for the QCD Debye mass and its evaluation are reviewed in
a non-perturabtive framework for the study of screening of general static
sources. While it is possible to perturbatively integrate over scales $\sim T$
and thus construct a 3d effective theory, the softer scales $\sim gT$ and $\sim
g^2T$ are strongly coupled for temperatures $\lsim 10^7$ GeV and require
lattice simulations. Within the effective theory, a lattice treatment of
screening at finite quark densities $\mu \lsim 4/T$ is also possible.
SPIRES or
http://arXiv.org/abs/hep-ph/0010327
Topics in the Heavy Quark Expansion
Nikolai Uraltsev
Achievements in the heavy quark theory over the last decade are reviewed,
with the main emphasis put on dynamical methods which quantify nonperturbative
effects via application of the Operator Product Expansion. These include the
total weak decay rates of heavy flavor hadrons and nonperturbative corrections
to heavy quark sum rules. Two new exact superconvergent sum rules are derived;
they differ from the known ones in that they are finite and normalization point
independent in perturbation theory. A new hadronic parameter \bar\Sigma is
introduced which is a spin-nonsinglet analogue of \bar\Lambda=M_B-m_b; it is
expected to be about 0.25GeV. The first sum rule implies the bound \rho^2 > 3/4
for the slope of the Isgur-Wise function. The heavy quark potential is
discussed and its connection to the infrared contributions in the heavy quark
mass. Among applications extraction of |V_cb| from the total semileptonic and
from the B->D^* zero recoil rates is addressed, as well as extracting |V_ub|
from \Gamma_sl(b->u). Practical aspects of local quark-hadron duality are
briefly discussed.
SPIRES or
http://arXiv.org/abs/hep-ph/0010328
Rho meson properties in nuclear matter from QCD sum rules
Andreas Nyffeler (CPT Marseille)
We study the properties of rho mesons in nuclear matter by means of QCD sum
rules at finite density. For increased sensitivity, we subtract out the vacuum
contributions. With the spectral function as estimated in the literature, these
subtracted sum rules are found to be not well satisfied. We suppose that Landau
singularities from higher resonance states in the nearby region in this channel
are the cause for this failure.
SPIRES or
http://arXiv.org/abs/hep-ph/0010329
Charm quark mass from QCD sum rules for the charmonium system
M. Eidemuller and M. Jamin
In this work, the charm quark mass is obtained from a QCD sum rule analysis
of the charmonium system. In our investigation we include results from
nonrelativistic QCD at next-to-next-to-leading order. Using the pole mass
scheme, we obtain a value of $M_c=1.70\pm 0.13$ GeV for the charm pole mass.
The introduction of a potential-subtracted mass leads to an improved scale
dependence. The running ${\rm \bar{MS}}$-mass is then determined to be
$m_c(m_c) = 1.23 \pm 0.09$ GeV.
SPIRES or
http://arXiv.org/abs/hep-ph/0010334
Introduction to Diffractive Photoprocesses
G. Shaw (University of Manchester)
The objectives of my talk are to provide a very brief introduction to
diffractive photoprocesses in general and the colour dipole model in
particular; and to comment on possible gluon saturation effects at HERA and
beyond.
SPIRES or
http://arXiv.org/abs/hep-ph/0011007
Screening length, dispersion relations and quark potential in thermo field dynamics
Wanyun Zhao and F.C. Khanna (Univ. of Alberta, Canada)
The screening length in a quark-gluon plasma, the dispersion relations of
thermal gluon self-energy and the quark potential at high temperature are
studied within thermo field dynamics framework. By calculation of the real and
imaginary parts, of the gluon self-energy in one-loop order in thermo field
dynamics, we obtain an expression for the screening length in a quark-gluon
plasma and the dispersion relation between the real and imaginary parts. At
high temperature, using photon exchange between electron-positron in a skeleton
expansion and ladder approximation, the screened Coulomb potential is obtained,
and using one-gluon and two-gluon exchange between a quark-antiquark, we get an
expression for the screened quark potential up to $O(g amplitudes of generic
process taking place in a many body system in equilibrium at temperature T. The
relationship of the scattering and decay amplitudes as calculated in Thermo
Field Dynamics to the conventional techniques is established. It is shown that
in many cases the calculations are relatively easy in TFD.
SPIRES or
http://arXiv.org/abs/hep-ph/0011182
Constraints on color dipole-nucleon cross section from diffractive heavy quarkonium production
Katsuhiko Suzuki (Univ. of Tokyo), Kazunori Itakura (RBRC)
We study the hard color dipole-nucleon cross section within perturbative QCD
and discuss its relation to observables in diffractive leptoproduction of heavy
quarkonium. The dipole cross section calculated with the unintegrated gluon
density of the nucleon substantially differs from the well-known perturbative
form $\sigma_{dip} \sim b^2$ for $b > 0.3$fm, where $b$ is the transverse
separation of the dipole. We show the measured ratio of $\psi '$ to $J / \psi$
photoproduction cross sections constrains the dipole cross section at
intermediate $b$, and in fact excludes the simple $\sigma_{dip} \sim b^2$
behavior. We also calculate the $t$-slopes of the diffractive $J / \psi, \psi
'$ productions. We emphasize the difference of $t$-slopes, $B_{J/\psi} -
B_{\psi '}$, is dominated by the dipole-nucleon dynamics. This difference is
found to be about $0.3 {GeV}^{-2}$ with our dipole cross section.
SPIRES or
http://arXiv.org/abs/hep-ph/0011186
Some comments on the missing charm puzzle
Alexander Lenz
A Toy Model of Colour Screening in the Proton
Johann Dischler and Torbj\"orn Sj\"ostrand
In hadronic collisions, the mini-jet cross section is formally divergent in
the limit pT -> 0. We argue that this divergence is tamed by some effective
colour correlation length scale of the hadron. A toy model of the hadronic
structure is introduced, that allows an estimate of the screening effects, and
especially their energy dependence.
SPIRES or
http://arXiv.org/abs/hep-ph/0011282
Spin effects in diffractive hadron photoproduction
S.V. Goloskokov
We study spin asymmetries in diffractive $Q \bar Q$ and vector meson
production which are sensitive to the spin-dependent part of the
two-gluon-nucleon coupling. It is found that the $A_{ll}$ and $A_{lT}$
asymmetry in diffractive reactions can be used to study polarized gluon
distributions of the proton.
SPIRES or
http://arXiv.org/abs/hep-ph/0011341
Color degrees of freedom in nuclear collisions and charmonium suppression
J\"org H\"ufner, Boris Z. Kopeliovich and Alberto Polleri
In high energy nuclear collisions, the Glauber model is commonly used to
evaluate $J/\psi$ suppression due to inelastic interaction with colorless bound
nucleons. This requires an effective value for the $J/\psi$-nucleon absorption
cross section which is larger than theoretically expected. On the other hand,
multiple nucleon-nucleon collisions mediated by color exchange interactions,
excite their color degrees of freedom. We investigate the importance of this
effect and conclude that the related corrections are important to explain the
effective value extrapolated from experiment.
SPIRES or
http://arXiv.org/abs/hep-ph/0012010
Open Charm Enhancement in Pb+Pb Collisions at SPS
M.I. Gorenstein, A.P. Kostyuk, H. Stoecker and W. Greiner
The statistical coalescence model for the production of open and hidden charm
is considered within the canonical ensemble formulation. The data for the
J/\psi multiplicity in Pb+Pb collisions at 158 A GeV are used for the model
prediction of the open charm yield. We find a strong enhancement of the open
charm production, by a factor of about 2--4, over the standard hard-collision
model extrapolation from nucleon-nucleon to nucleus-nucleus collisions. A
possible mechanism of the open charm enhancement in A+A collisions at the SPS
energies is proposed.
SPIRES or
http://arXiv.org/abs/hep-ph/0012015
Fluctuations of the transverse energy in Pb+Pb collisions and J/psi suppression
J\"org H\"ufner, Boris Z. Kopeliovich and Alberto Polleri
The observed $J/\psi$ suppression in Pb+Pb collisions shows a break in the
domain of large transverse energy. It has been proposed to extend the validity
of existing models in this domain by introducing an ad hoc factor responsible
for transverse energy fluctuations. We derive this result with some
modifications.
SPIRES or
http://arXiv.org/abs/nucl-th/0012003
Supersymmetric origin of a low $a_{J/\psi}$ CP asymmetry
A. Masiero, M. Piai (SISSA) and O. Vives (U. Valencia-IFIC)
We show that general Minimal Supersymmetric extensions of the Standard Model
(MSSM) allow for a CP asymmetry in B --> J/psi K(S) well bellow the SM
expectations with dominant Supersymmetric contributions to epsilon_K and
epsilon'/epsilon. Indeed, we provide an explicit example of an MSSM with
non-universal soft breaking terms fully consistent with the low results of this
asymmetry recently reported by Babar and Belle collaborations.
SPIRES or
http://arXiv.org/abs/hep-ph/0012096
Heavy Flavour Physics: On Its More Than 50 Years Of History, Its Future And The Rio Manifesto
I.I. Bigi
After a reminder about how $\Delta S\neq 0$ physics has been instrumental for
the development of the Standard Model I sketch theoretical technologies for
dealing with nonperturbative QCD in heavy flavour decays and state predictions
for CP odd effects as they were made in 1998. I review the exciting
developments in heavy flavour physics as presented at this conference. A
central message is presented in the `Rio Manifesto' where I recapitulate the
lessons we have learnt from charm physics, point out the special role future
dedicated charm studies can play in revealing the presence of New Physics and
give an introduction to the relevant phenomenology focussed on CP studies.
SPIRES or
http://arXiv.org/abs/hep-ph/0012161
On the $\sigma_L/\sigma_T$ Ratio in Polarized Vector Meson Photoproduction
S.V.Goloskokov
We study the spin-dependent cross-sections of vector meson photoproduction
for longitudinally and transversely polarized photons within a QCD- model. The
dependence of the $\sigma_T/\sigma_L$ ratio on the photon virtuality and on the
meson wave function is analysed.
SPIRES or
http://arXiv.org/abs/hep-ph/0012307
Open and Hidden Charm Production in Au+Au Collisions at RHIC Energies
M.I. Gorenstein, A.P. Kostyuk, L. McLerran, H. Stoecker and W. Greiner
We consider various possibilities for the production of open charm and J/psi
at RHIC energies in heavy ion collisions. We discuss several recently developed
pictures for J/psi production and argue that a measurement at RHIC energies is
crucial for disentangling these different descriptions.
SPIRES or
http://arXiv.org/abs/hep-ph/0012292
J/Psi suppression in colliding nuclei: statistical model analysis
Dariusz Prorok and Ludwik Turko
We consider the $J/\Psi$ suppression at a high energy heavy ion collision. An
ideal gas of massive hadrons in thermal and chemical equilibrium is formed in
the central region. The finite-size gas expands longitudinally in accordance
with Bjorken law. The transverse expansion in a form of the rarefaction wave is
taken into account. We show that $J/\Psi$ suppression in such an environment,
when combined with the disintegration in nuclear matter, gives correct
evaluation of NA38 and NA50 data in a broad range of initial energy densities.
SPIRES or
http://arXiv.org/abs/hep-ph/0012382
On the Energy Loss of High Energy Quarks in a Finite-Size Quark-Gluon Plasma
B. G. Zakharov
We study within the light-cone path integral approach the induced gluon
emission from a fast quark passing through a finite-size QCD plasma. We show
that the leading log approximation used in previous studies fails when the
gluon formation length becomes of the order of the length of the medium
traversed by the quark. Calculation of the energy loss beyond the leading log
approximation gives the energy loss which grows logarithmically with quark
energy contrary to the energy independent prediction of the leading log
approximation.
SPIRES or
http://arXiv.org/abs/hep-ph/0012360
Screening Corrections in Photo and DIS Production of $J/\Psi$
E. Gotsman (Tel Aviv U.), E. Ferreira (UFRJ), E. Levin, U. Maor and E.
Photo and DIS production of $J/\Psi$ are investigated and compared with
calculations based on pQCD in the LLA approximation without and with screening
corrections. The calculation includes corrections induced by the real part of
the production amplitude, the skewed (off diagonal) gluon structure function
and the relativistic Fermi motion within the charmonium system. Our pQCD
results are also compared with the predictions obtained from a Regge type two
Pomeron model. Our results suggest some preference for our screened model, but
the available data does not enable us to exclude any of the three models we
have examined. The properties of these models, when extrapolated to both low
and very high energies may provide a more effective discrimination between the
different parameterizations.
SPIRES or
http://arXiv.org/abs/hep-ph/0101142
Heavy Quark Production at High Energy
R.D. Ball and R.K. Ellis
We report on QCD radiative corrections to heavy quark production valid at
high energy. The formulae presented will allow a matched calculation of the
total cross section which is correct at $O(\as^3)$ and includes resummation of
all terms of order $\as^3 [\as \ln (s/m^2)]^n$. We also include asymptotic
estimates of the effect of the high energy resummation. A complete description
of the calculation of the heavy quark impact factor is included in an appendix.
SPIRES or
http://arXiv.org/abs/hep-ph/0101199
A Unified Model of Exclusive $\rho^0$, $\phi$ and $\jpsi$ Electroproduction
A Donnachie, J Gravelis and G Shaw (University of Manchester)
A two-component model is developed for diffractive electroproduction of
$\rho^0$, $\phi$ and $\jpsi$, based on non-perturbative and perturbative
two-gluon exchange. This provides a common kinematical structure for
non-perturbative and perturbative effects, and allows the role of the
vector-meson vertex functions to be explored independently of the production
dynamics. A good global description of the vector-meson data is obtained.
SPIRES or
http://arXiv.org/abs/hep-ph/0101221
Remarks on photon-hadron interactions
E. Comay
Theoretical aspects of VMD and related approaches to real photon-hadron
interaction are discussed. The work relies on special relativity, properties of
linearly polarized photons, angular momentum conservation and relevant
experiments. It is explained why VMD and similar approaches should not be
regarded as part of a theory but, at most, as phenomenological models. A
further experiment pertaining to this issue is suggested.
SPIRES or
http://arXiv.org/abs/hep-ph/0101312
Mott effect at the chiral phase transition and anomalous J/Psi suppression
Gerhard R.G. Burau, David B. Blaschke, Yuri L. Kalinovsky
We investigate the in-medium modification of the charmonium break-up
processes due to the Mott effect for light (pi) and open-charm (D, D*) mesons
at the chiral/deconfinement phase transition. A model calculation for the
process J/Psi + pi -> D + \bar D* + h.c. is presented which demonstrates that
the Mott effect for the D-mesons leads to a threshold effect in the thermal
averaged break-up cross section. This effect is suggested as an explanation of
the phenomenon of anomalous J/Psi suppression in the CERN NA50 experiment.
SPIRES or
http://arXiv.org/abs/nucl-th/0012030
SPIRES or
www
J/\psi production through resolved photon processes at e+ e- colliders
R.M. Godbole (IISc., Bangalore), D. Indumathi (IMSc., Chennai), M.
We consider J/psi photoproduction in e+ e- as well as linear photon
colliders. We find that the process is dominated by the resolved photon
channel. Both the once-resolved and twice-resolved cross-sections are sensitive
to (different combinations of) the colour octet matrix elements. Hence, this
may be a good testing ground for colour octet contributions in NRQCD. On the
other hand, the once-resolved J/psi production cross-section, particularly in a
linear photon collider, is sensitive to the gluon content of the photon. Hence
these cross-sections can be used to determine the parton distribution
functions, especially the gluon distribution, in a photon, if the colour octet
matrix elements are known.
SPIRES or
http://arXiv.org/abs/hep-ph/0101333
Searches for Rare and Forbidden Decays of Charm: Recent Results from FNAL
A. J. Schwartz
We review results on rare and forbidden decays of D^0, D^+, and D^+_s mesons
from experiments at FNAL. The decay modes studied have two leptons in the final
state and, if observed, would constitute evidence for flavor-changing
neutral-current, lepton-flavor-violating, or lepton-number-violating processes.
To date, no evidence for these decays has been observed and upper limits are
obtained for their branching fractions. These limits can constrain various
extensions to the Standard Model. We present new upper limits from FNAL E791 on
the branching fractions for more than two dozen three- and four-body decay
modes.
SPIRES or
http://arXiv.org/abs/hep-ex/0101050
Transverse energy distributions and $J/\psi$ production in Pb+Pb collisions
A. K. Chaudhuri
We have analysed the latest NA50 data on transverse energy distributions and
$J/\psi$ suppression in Pb+Pb collisions. The transverse energy distribution
was analysed in the geometric model, where AA collisions are written in terms
of NN collisions, taking into account the fluctuations in the number of NN
collisions at fixed impact parameter. Analysis suggests that in Pb+Pb
collisions, nucleons are more transparent than in other AA collisions,
producing less $E_T$ in individual NN collisions. The transverse energy
dependence of the $J/\psi$ was obtained assuming that charmonium suppression is
100% effective above a threshold density. Good fit to data is obtained if the
fluctuations in number of NN collisions at fixed impact parameter is taken into
account.
SPIRES or
http://arXiv.org/abs/hep-ph/0102038
Heavy-quarkonium hadron cross section in QCD at leading twist
F. Arleo, P.-B. Gossiaux, T. Gousset, and J. Aichelin
We compute the total cross section of a heavy quarkonium on a hadron target
in leading twist QCD, including target mass corrections. Our method relies on
the analytical continuation of the operator product expansion of the scattering
amplitude, obtained long ago by Bhanot and Peskin. The cross section has a
simple partonic form, which allows us to investigate the phenomenology of J/psi
and Upsilon dissociation by both pions and protons.
SPIRES or
http://arXiv.org/abs/hep-ph/0102095
The p_T Spectrum in Heavy-Flavour Photoproduction
M. Cacciari, S. Frixione and P. Nason
We consider the transverse-momentum distribution of heavy flavours in
photon-hadron collisions. We present a formalism in which large
transverse-momentum logarithms are resummed to the next-to-leading level, and
mass effects are included exactly up to order alpha_em alpha_s^2, so as to
retain predictivity at both small and large transverse momenta.
Phenomenological applications relevant to charm photoproduction at HERA are
given.
SPIRES or
http://arXiv.org/abs/hep-ph/0102134
Gluon depletion and J/psi suppression in pA collisions
R.C.Hwa
The gluon distribution of a nucleon propagating through a nucleus can change
depending on how far the penetration depth is. It is a nonperturbative process
that we describe by an evolution equation. The kernel of the integral equation
is to be determined by a phenomenological study of J/psi suppression in pA
collision. The data of E866 on alpha(x_F) shows significant dependence on x_F
at large x_F. It presents a feature that has not been explained by any hadronic
absorption model. We show that gluon depletion is a simple mechanism that can
account for it. The result has far-reaching implications on the role of partons
in nuclear collisions.
SPIRES or
http://arXiv.org/abs/hep-ph/0102154
Diffractive eta_c photo-and electroproduction with the perturbative QCD Odderon
J. Bartels, M. A. Braun, D. Colferai, G. P. Vacca
Using a set of new odderon states, we calculate their contribution to the
diffractive eta_c photo- and electroproduction process. Compared to previous
simple 3-gluon exchange calculations we find an enhancement of about one order
of magnitude in the cross section. The t-dependence of the cross section
exhibits a dip structure in the small t region.
SPIRES or
http://arXiv.org/abs/hep-ph/0102221
Possible Color Octet Quark-Anti-Quark Condensate in the Instanton Model
Thomas Schaefer
Inspired by a recent proposal for a Higgs description of QCD we study the
possible formation of a color-octet/flavor-octet quark-anti-quark condensate in
the instanton liquid model. For this purpose we calculate two-point correlation
functions of color-singlet and octet quark-anti-quark operators. We find long
range order in the standard $<\bar{\psi}\psi>$ channel, but not in the
color-octet channel. We emphasize that similar calculations in lattice QCD can
check whether or not a color-flavor locked Higgs phase is realized in QCD at
zero temperature and baryon density.
SPIRES or
http://arXiv.org/abs/hep-lat/0102007
SPIRES or
www
Radiative Corrections to the Single Spin Asymmetry in Heavy Quark Photoproduction
N.Ya.Ivanov (YerPI)
We analyze in the framework of pQCD the properties of the single spin
asymmetry in heavy flavor production by linearly polarized photons. At leading
order, the parallel- perpendicular asymmetry in azimuthal distributions of both
charm and bottom quark is predicted to be about 20% in a wide region of initial
energy. Using the soft gluon resummation formalism, we have calculated the
next-to-leading order corrections to the asymmetry to next-to-leading
logarithmic accuracy. It is shown that radiative corrections practically do not
affect the Born predictions for the azimuthal asymmetry at energies of the
fixed target experiments. Both leading and next-to-leading order predictions
for the asymmetry are insensitive to within few percent to theoretical
uncertainties in the QCD input parameters: $m_{Q}$, $\mu_{R}$, $\mu_{F}$,
$\Lambda_{QCD}$ and in the gluon distribution function. Our analysis shows that
nonperturbative corrections to a $B$-meson azimuthal asymmetry due to the gluon
transverse motion in the target are negligible. We conclude that measurements
of the single spin asymmetry would provide a good test of pQCD applicability to
heavy flavor production at fixed target energies.
SPIRES or
http://arXiv.org/abs/hep-ph/0102328
On a possible manifestation of f_1 trajectory in J/psi photoproduction
Dayeeta Roy (1), Toshiyuki Morii (2)and Alexander I. Titov (3) ((1)
We analyze a possible manifestation of f_1-trajectory in elastic J/psi
photoproduction at high energy and large momentum transfer. Inspite of the
small contribution of f_1-trajectory in total cross sections, it becomes
significant in various spin observables. In particular, we show that the
crucial test for f_1-exchange can be made by measuring the single beam- and
double parity- and beam-target asymmetries at large momentum transfers, where a
strong deviation from the exchange of conventional Pomerons is expected. This
effect is caused by the interference of natural (Pomeron) and unnatural (f_1)
parity exchange parts of amplitude in the region where their contributions
become comparable to each other and might be interesting to observe in
forthcoming experiments, if feasible. .
SPIRES or
http://arXiv.org/abs/hep-ph/0103004
Heavy Flavor Enhancement as a Signal of Color Deconfinement
A.P. Kostyuk, M.I. Gorenstein and W. Greiner
We argue that the color deconfinement in heavy ion collisions may lead to
enhanced production of hadrons with open heavy flavor (charm or bottom). We
estimate the upper bound of this enhancement.
SPIRES or
http://arXiv.org/abs/hep-ph/0103057
Open charm enhancement by secondary interactions in relativistic nucleus-nucleus collisions?
W. Cassing (Univ. of Giessen), L.A. Kondratyuk (ITEP Moscow), G.I.
We calculate open charm production in $Pb+Pb$ reactions at SPS energies
within the HSD transport approach - which is based on string, quark, diquark
($q, \bar{q}, qq, \bar{q}\bar{q}$) and hadronic degrees of freedom - including
the production of open charm pairs from secondary 'meson'-'baryon' (or
quark-diquark and antiquark-diquark) collisions. It is argued that at collision
energies close to the $c\bar{c}$ pair threshold the dominant production
mechanism is related to the two body (or quasi two body) reactions $\pi N \to
\bar{D} (\bar{D^*}) \Lambda_c, (\Sigma_c)$. Estimates within the framework of
the Quark-Gluon String model suggest cross sections of a few $\mu b$ for $\pi N
\to \bar{D} \Lambda_c$ in the region of 1 GeV above threshold. The dynamical
transport calculations for $Pb + Pb$ at 160 A$\cdot$GeV indicate that the open
charm enhancement reported by the NA50 Collaboration might be due to such
secondary reaction mechanisms.
SPIRES or
http://arXiv.org/abs/hep-ph/0103073
Thermal versus Direct $J/\Psi$ Production in Ultrarelativistic Heavy-Ion Collisions
L. Grandchamp and R. Rapp
The production of $J/\Psi$ mesons in central collisions of heavy nuclei is
investigated as a function of collision energy. Two contributions are
considered simultaneously: early (hard) production coupled with subsequent
suppression in a Quark-Gluon Plasma, as well as thermal recombination of
primordially produced $c$ and $\bar c$ quarks at the hadronization transition.
Whereas the former still constitutes the major fraction of the observed
$J/\Psi$ abundance at SpS energies, the latter dominates the yield at RHIC. The
resulting excitation function for the number of $J/\Psi$'s over open charm
pairs exhibits nontrivial structure around $\sqrt{s} \simeq 30$ AGeV, evolving
into a significant rise towards maximal RHIC energy. We study this feature
within different (thermal) scenarios for $J/\Psi$ suppression, including
parton-induced quasifree destruction as a novel mechanism.
SPIRES or
http://arXiv.org/abs/hep-ph/0103124
On the size of hadrons
Hans-Christian Pauli (1) and Asmita Mukherjee (2) ((1) MPI Kernphysik,
The form factor and the mean-square radius of the pion are calculated
analytically from a parametrized form of a $q\bar q$ wave function. The
numerical wave function was obtained previously by solving numerically an
eigenvalue equation for the pion in a particular model. The analytical formulas
are of more general interest than just be valid for the pion and can be
generalized to the case with unequal quark masses. Two different
parametrizations are investigated. Because of the highly relativistic problem,
noticable deviations from a non-relativistic formula are obtained.
SPIRES or
http://arXiv.org/abs/hep-ph/0103150
Gauge Invariance, Color-Octet Vector Resonances and Double Technieta Production at the Tevatron
Alfonso R. Zerwekh and Rogerio Rosenfeld
We show that the usual vector meson dominance method does not apply directly
to the mixing of a color-octet vector boson (color-octet technirho) with the
gluon because of gauge invariance. We propose a gauge invariant method where
one works in a physical basis with mass eigenstate fields. As a result, we show
that the physical technirho does not couple to two gluons, contrary to the
general belief. Consequences for the production of a pair of color-octet,
isosinglet technipions (technietas) at Fermilab is analysed by means of a
simulation of the signal and background, including kinematical cuts. We find
that the signal is too small to be observed.
SPIRES or
http://arXiv.org/abs/hep-ph/0103159
Kaon and Charm Physics: Theory
Gerhard Buchalla (CERN)
We introduce and discuss basic topics in the theory of kaons and charmed
particles. In the first part, theoretical methods in weak decays such as
operator product expansion, renormalization group and the construction of
effective Hamiltonians are presented, along with an elementary account of
chiral perturbation theory. The second part describes the phenomenology of the
neutral kaon system, CP violation, $\varepsilon$ and
$\varepsilon'/\varepsilon$, rare kaon decays ($K\to\pi\nu\bar\nu$, $K_L\to\pi^0
e^+e^-$, $K_L\to\mu^+\mu^-$), and some examples of flavour physics in the charm
sector.
SPIRES or
http://arXiv.org/abs/hep-ph/0103166
Generalized dipole polarizabilities and the spatial structure of hadrons
A.I. L'vov (1), S. Scherer (2), B. Pasquini (3), C. Unkmeir (2), D.
We present a phenomenological discussion of spin-independent, generalized
dipole polarizabilities of hadrons entering the virtual Compton scattering
process gamma* h -> gamma h. We introduce a new method of obtaining a tensor
basis with appropriate Lorentz-invariant amplitudes which are free from
kinematical singularities and constraints. We then motivate a gauge-invariant
separation into a generalized Born term containing ground-state properties
only, and a residual contribution describing the model-dependent internal
structure. The generalized dipole polarizabilities are defined in terms of
Lorentz-invariant residual amplitudes. Particular emphasis is laid on a
physical interpretation of these quantities as characterizing the spatial
distributions of the induced electric polarization and magnetization of
hadrons. It is argued that three dipole polarizabilities, namely the
longitudinal electric alpha_L(q^2), the transverse electric alpha_T(q^2), and
the magnetic beta(q^2) ones are required in order to fully reconstruct local
polarizations induced by soft external fields in a hadron. One of these
polarizabilities, alpha_T(q^2), describes an effect of higher order in the soft
final-photon momentum q'. We argue that the associated spatial distributions
obtained via the Fourier transforms in the Breit frame are meaningful even for
such a light particle as the pion. The spatial distributions are determined at
large distances r ~ 1/m_pi for pions, kaons, and octet baryons by use of ChPT.
SPIRES or
http://arXiv.org/abs/hep-ph/0103172
Heavy quarkonium production in double Pomeron exchange processes in perturbative QCD
Feng Yuan (Heidelberg U.)
We calculate the heavy quarkonium production in double pomeron exchange
processes in perturbative QCD by using two-gluon exchange model. For the
$P$-wave $\chi_J$ productions, we find $\chi_1$ and $\chi_2$ production
amplitudes which vanish in the forward scattering limit. We also calculate
direct $J/\psi(\Upsilon)+\gamma$ production in the same approach, and these
direct contributions are much smaller than the feeddown contributions from the
$P$-wave states.
SPIRES or
http://arXiv.org/abs/hep-ph/0103213
Chiral Symmetry in Charmonium - Pion Cross Section
F.S. Navarra, M. Nielsen and M.R. Robilotta
We perform a non-perturbative calculation of the $J/\Psi-\pi$ cross section
using a $SU(2)\times SU(2)$ effective Lagrangian. Our results differ from those
of previous calculations, specially in the description of vertices involving
pions.
SPIRES or
http://arXiv.org/abs/nucl-th/0103051
Exclusive decay of $J/\Psi$ into a lepton pair combined with light hadrons
J.P. Ma
We study the exclusive decay of $J/\Psi$ into a lepton pair combined with
light hadrons in the kinematic region, specified by that the total energy of
the light hadrons is much smaller than $m_c$, the mass of the $c$-quark. In
this region, the nonperturbaive effect related to $J/\Psi$ and that related to
the light hadrons can be separated, the former is represented by a NRQCD matrix
element, while the later is represented by a matrix element of a correlator of
electric chromofields. The results are obtained in a axial gauge by assumming
that contributions from two-gluon emmssion are dominant. But we can show that
these results can be obtained without the assumption in arbitrary gauges. A
discussion of the results are presented.
SPIRES or
http://arXiv.org/abs/hep-ph/0103236
Measurement of hybrid content of heavy quarkonia using lattice NRQCD
Tommy Burch, Kostas Orginos, and Doug Toussaint
Using lowest-order lattice NRQCD to create heavy meson propagators and
applying the spin-flip interaction, $c_B^{}
\frac{-g}{2m_q}\vec\sigma\cdot\vec{B}$, at varying intermediate time slices, we
compute the off-diagonal matrix element of the Hamiltonian for the
quarkonium-hybrid two-state system. Thus far, we have results for one set of
quenched lattices with an interpolation in quark mass to match the
$J^{PC}=1^{--}$ bottomonium spectrum. After diagonalization of the two-state
Hamiltonian, we find the ground state of bottomonium to show a $0.0035(1)c_B^2$
(with $c_B^2 \sim 1.5-3.1$) probability admixture of hybrid, $|Q\bar{Q}g>$.
SPIRES or
http://arXiv.org/abs/hep-lat/0103025
Heavy quark photoproduction at THERA
P. Jankowski, M. Krawczyk (University of Warsaw), M. Wing (McGill
Measurements of heavy quark production at a possible future $ep$ facility,
THERA, would provide valuable information on the structure of the photon. QCD
cross-section predictions are made at LO for both charm and beauty production
and their sensitivity to current parametrisations of the photon parton
densities is investigated.
SPIRES or
http://arXiv.org/abs/hep-ph/0103330
Charm Physics and the Poor Sleeper's Impatience
I.I. Bigi
After a short review of the theoretical tools available to describe heavy
flavour physics I sketch the present profile of the weak dynamics of charm
hadrons with respect to lifetimes, oscillations and CP violation. I argue that
comprehensive studies of charm decays provide novel portals to New Physics and
suggest some benchmark figures for desirable sensitivities.
SPIRES or
http://arXiv.org/abs/hep-ph/0104008
J/Psi Production at RHIC in a QGP
Robert L. Thews and Johann Rafelski
In central collisions at RHIC, the initial production of heavy quarks will
for the first time yield multiple pairs of c-cbar in each central event. If a
region of deconfined quarks and gluons is subsequently formed, a new mechanism
for the formation of heavy quarkonium bound states will be activated. This will
result from the mobility of heavy quarks in the deconfined region, such that
bound states can be formed from a quark and an antiquark which were originally
produced in separate incoherent interactions. Our model estimates of this
effect predict a dramatic increase in the number of observed J/Psi at RHIC,
over that predicted from extrapolation of color-screening or gluon dissociation
mechanisms from the lower CERN-SPS energies. The centrality and energy
dependence of this effect should be readily observable by the Star and Phenix
detectors. Thus the J/Psi abundance at RHIC will continue to provide a
signature of QGP formation. However, it is in this environment a more useful
probe, since contrary to prior expectations this large predicted J/Psi
abundance should be relatively easy to measure.
SPIRES or
http://arXiv.org/abs/hep-ph/0104025
Charmonium Production off Nuclei: from SPS to RHIC
B.Z. Kopeliovich
Physics of charmonium suppression in nuclear collisions drastically changes
between the energies of SPS and RHIC. Mechanisms suppressing charmonia at SPS
are reviewed, neither of which is important at RHIC. On the other hand,
coherence, or shadowing of c-quarks and gluons barely seen at SPS, become a
dominant effect at RHIC providing a much stronger suppression. A onset of
coherence at Fermilab energies explains the observed cross section ratio
steeply falling at large Feynman x_F. In nuclear collisions variation of
charmonium suppression with x_F suggests a sensitive probe for QGP.
SPIRES or
http://arXiv.org/abs/hep-ph/0104032
J/psi plus dijet associated production in two-photon collisions
M. Klasen, B.A. Kniehl, L. Mihaila, M. Steinhauser (Hamburg
We study the production of a J/psi meson in association with one or two jets
in gamma gamma collisions concentrating on the direct-photon contribution,
which is expected to be dominant for large J/psi-meson transverse momentum
and/or large dijet invariant mass. We work at leading order in the
factorization formalism of nonrelativistic QCD and include all relevant
colour-octet processes. We present distributions in J/psi-meson transverse
momentum and rapidity appropriate for CERN LEP2, a future e^+e^- linear
collider, and a possible gamma gamma collider mode of the latter. In the case
of the e^+e^- linear collider, we assume the beamstrahlung spectrum appropriate
for DESY TESLA.
SPIRES or
http://arXiv.org/abs/hep-ph/0104044
J/psi Suppression and Enhancement in Au+Au Collisions at the BNL RHIC
M.I. Gorenstein, A.P. Kostyuk, H. Stoecker and W. Greiner
We consider the production of the J/psi mesons in heavy ion collisions at
RHIC energies in the statistical coalescence model with an exact (canonical
ensemble) charm conservation. The c\bar{c} quark pairs are assumed to be
created in the primary hard parton collisions, but the formation of the open
and hidden charm particles takes place at the hadronization stage and follows
the prescription of statistical mechanics. The dependence of the J/psi
production on both the number of nucleon participants and the collision energy
is studied. The model predicts the J/psi suppression for low energies, whereas
at the highest RHIC energy the model reveals the J/psi enhancement.
SPIRES or
http://arXiv.org/abs/hep-ph/0104071
Diffractive beauty photoproduction as a short distance probe of QCD pomeron
V. R. Zoller (ITEP, Moscow)
High-energy open beauty photoproduction probes the vacuum exchange at
distances $\sim 1/m_b$ and detects significant corrections to the BFKL
asymptotics coming from the subleading vacuum poles. We show that the interplay
of leading and subleading vacuum exchanges gives rise to the cross section
$\sigma^{b\bar b}(W)$ growing much faster than it is prescribed by the exchange
of the leading pomeron trajectory with intercept
$\alpha_{\Pom}(0)-1=\Delta_{\Pom}=0.4$. Our calculations within the color
dipole BFKL model are in agreement with the recent determination of
$\sigma^{b\bar b}(W)$ by the H1 collaboration. The comparative analysis of
diffractive photoproduction of beauty, charm and light quarks exhibits the
hierarchy of pre-asymptotic pomeron intercepts which follows the hierarchy of
corresponding hardness scales. We comment on the phenomenon of decoupling of
soft and subleading BFKL singularities at the scale of elastic
$\Upsilon(1S)$-photoproduction which results in precocious color dipole BFKL
asymptotics of the process $\gamma p \to \Upsilon p$.
SPIRES or
http://arXiv.org/abs/hep-ph/0104093
Interplay of soft and hard processes and hadron $p_T$ spectra in $pA$ and $AA$ collisions
Enke Wang and Xin-Nian Wang
Motivated by a schematic model of multiple parton scattering within the
Glauber formalism, the transverse momentum spectra in $pA$ and $AA$ collisions
are analyzed in terms of a nuclear modification factor with respect to $pp$
collisions. The existing data at the CERN Super Proton Synchrotron (SPS)
energies are shown to be consistent with the picture of Glauber multiple
scattering in which the interplay between soft and hard processes and the
effect of absorptive processes lead to nontrivial nuclear modification of the
particle spectra. Relative to the additive model of incoherent hard scattering,
the spectra are enhanced at large $p_T$ (hard) by multiple scattering while
suppressed at low $p_T$ (soft) by absorptive correction with the transition
occurring at around a scale $p_0\sim 1-2$ GeV/$c$ that separates soft and hard
processes. Around the same scale, the $p_T$ spectra in $pp$ collisions also
change from an exponential form at low $p_T$ to a power-law behavior at high
$p_T$. At very large $p_T\gg p_0$, the nuclear enhancement is shown to decrease
like $1/p_T^2$. Implications of these nuclear effects on the study of jet
quenching, parton thermalization and collective radial flow in high-energy $AA$
collisions are discussed.
SPIRES or
http://arXiv.org/abs/nucl-th/0104031
SPIRES or
www
The color dipole approach to the Drell-Yan process in pA collisions
B.Z. Kopeliovich, J. Raufeisen, A.V. Tarasov
In the target rest frame and at high energies, Drell-Yan (DY) dilepton
production looks like bremsstrahlung of massive photons, rather than parton
annihilation. The projectile quark is decomposed into a series of Fock states.
Configurations with fixed transverse separations are interaction eigenstates
for pp scattering. The DY cross section can then be expressed in terms of the
same color dipole cross section as DIS. This approach is especially suitable to
describe nuclear effects, since it allows to apply Glauber multiple scattering
theory. We go beyond the Glauber eikonal approximation by taking into account
transitions between interaction eigenstates. We calculate nuclear shadowing at
large Feynman-x_F for DY in proton-nucleus collisions, compare to existing data
from E772 and make predictions for RHIC. Nuclear effects on the transverse
momentum distribution are also investigated.
SPIRES or
http://arXiv.org/abs/hep-ph/0104155
The photoproduction of vector mesons
J.-M. Laget
At high energy, the photoproduction or electroproduction of Vector Mesons
allow to prepare a beam of quark-antiquark pairs of a given flavor. At high
momentum transfer, the study of the scattering of these pairs on a nucleon
opens up an original window on the quark-gluon structure of hadronic matter,
which may eventually shed light on its gluonic content, on correlations between
quarks and on the van der Walls part of the interaction between hadrons.
SPIRES or
http://arXiv.org/abs/hep-ph/0107208
Color Transparency versus Quantum Coherence in Electroproduction of Vector Mesons off Nuclei
B.Z. Kopeliovich, J. Nemchik, A.Schaefer, A.V. Tarasov
So far no theoretical tool for the comprehensive description of exclusive
electroproduction of vector mesons off nuclei at medium energies has been
developed. We suggest a light-cone QCD formalism which is valid at any energy
and incorporates formation effects (color transparency), the coherence length
and the gluon shadowing. At medium energies color transparency (CT) and the
onset of coherence length (CL) effects are not easily separated. Indeed,
although nuclear transparency measured by the HERMES experiment rises with Q^2,
it agrees with predictions of the vector dominance model (VDM) without any CT
effects. Our new results and observations are: (i) the good agreement with the
VDM found earlier is accidental and related to the specific correlation between
Q^2 and CL for HERMES kinematics; (ii) CT effects are much larger than have
been estimated earlier within the two channel approximation. They are even
stronger at low than at high energies and can be easily identified by HERMES or
at JLab; (iii) gluon shadowing which is important at high energies is
calculated and included; (iv) our parameter-free calculations explain well
available data for variation of nuclear transparency with virtuality and energy
of the photon; (v) predictions for electroproduction of \rho and \phi are
provided for future measurements at HERMES and JLab.
SPIRES or
http://arXiv.org/abs/hep-ph/0107227
$J/\Psi$ suppression in an expanding hadron gas
Dariusz Prorok (Wroclaw Univ. ITP)
A model for $J/\Psi$ suppression at a high energy heavy ion collision is
presented. The main (and the only) reason for the suppression is $J/\Psi$
inelastic scattering within hadron matter. The hadron matter is in the form of
a multi-component non-interacting gas. Also the evolution of the gas, both
longitudinal and transverse, is taken into account. It is shown that under such
circumstances and with $J/\Psi$ disintegration in nuclear matter added,
$J/\Psi$ suppression evaluated agrees well with NA38 and NA50 data.
SPIRES or
http://arXiv.org/abs/hep-ph/0107260
$J/\Psi$ suppression at SPS, RHIC and LHC energies and the percolation of strings
N. Armesto, E. G. Ferreiro, F. del Moral and C. Pajares
We study the enhancement of $c \bar c$ pair production that takes place in
central heavy ion collisions due to the formation of clusters of strings. These
clusters produce heavy flavors more efficiently due to their higher color. We
discuss the competition between this mechanism and the well-known screening of
color charge, which, above a critical string density, reduces strongly the
probability of binding these $c \bar c$ pairs to form $J/\Psi$ particles. The
dependence of $J/\Psi$ suppression on the centrality shows a peak at both RHIC
and LHC energies corresponding to the percolation critical density.
SPIRES or
http://arXiv.org/abs/hep-ph/0107319
Quarkonium spectroscopy and perturbative QCD: massive quark-loop effects
N. Brambilla, Y. Sumino and A. Vairo
We study the spectra of the bottomonium and B_c states within perturbative
QCD up to order alpha_s^4. The O(Lambda_QCD) renormalon cancellation between
the static potential and the pole mass is performed in the epsilon-expansion
scheme. We extend our previous analysis by including the effects of non-zero
charm-quark mass in loops up to the next-to-leading non-vanishing order
epsilon^3. An extensive quantitative analysis is provided. Qualitatively the
effect of the charm mass is to widen the level spacings and the effect becomes
larger among higher levels. The size of non-perturbative and higher order
contributions is discussed by comparing the obtained predictions with the
experimental data. An agreement of the perturbative predictions and the
experimental data depends crucially on the precise value (inside the present
error) of alpha_s(M_Z). For the b-quark MSbar mass we obtain
$m_b^{\overline{MS}}(m_b^{\overline{MS}}) = 4190 \pm 20 \pm 25 \pm 4 ~ {MeV}$.
SPIRES or
http://arXiv.org/abs/hep-ph/0108084
QCD Sum Rules for Heavy Flavour Physics
Alexander Khodjamirian
Uses of QCD sum rules for heavy flavoured hadrons are discussed. "Standard"
applications such as the determination of the $b$, $c$ quark masses, the
calculation of $f_B$, $f_D$ and of the heavy-to-light form factors are
overviewed. Furthermore, a new approach to calculate the $B\to \pi\pi$ hadronic
matrix elements from QCD light-cone sum rules is described.
SPIRES or
http://arXiv.org/abs/hep-ph/0108205
Explicit Proof that Electroproduction of Transversely Polarized Vector Mesons Vanishes in Perturbative QCD
Pervez Hoodbhoy (University of Maryland and Quaid-e-Azam University)
By means of an explicit one-loop calculation, it is shown that the leading
twist contribution to the exclusive electroproduction of transversely polarized
vector mesons from the nucleon vanishes. This confirms the all-orders proof by
Collins and Diehl.
SPIRES or
http://arXiv.org/abs/hep-ph/0108214
Photoproduction of charmed vector mesons, $\gamma+N\to {\cal B}_c +\overline{D^*}$, with ${\cal B}_c=\Lambda_c$ or $\Sigma_c$
Michail P. Rekalo and Egle Tomasi-Gustafsson
The energy and the angular dependence of the associative vector charmed
${D^*}$-meson photoproduction, $\gamma+N\to {\cal B}_c+ \overline{D^*}$, with
${\cal B}_c=\Lambda_c$ or $\Sigma_c$, has been predicted in framework of
pseudoscalar D-meson exchange model. The behavior of the cross section is
driven by phenomenological form factors, which can be parametrized in terms of
two independent parameters. The predicted values of the cross section are
sizeable enough to be measured in the near threshold region.
SPIRES or
http://arXiv.org/abs/hep-ph/0108237
The Fadin-Lipatov-vertex in high-energy heavy quark and charmonium production
Philipp Hagler
Calculations of heavy quark and charmonium hadroproduction are presented in
the k_t-factorization approach. The resulting differential cross sections are
compared to experimental values and NLO collinear predictions. The application
of the full effective Fadin-Lipatov quark-antiquark- production-vertex has an
important influence on the results and in particular leads to a strong
suppression of certain color octet contributions which are related to the
outstanding problem of the production of polarized J/Psi.
SPIRES or
http://arXiv.org/abs/hep-ph/0109039
Charmonium decays: J/psi --> e+e- and eta_c --> gamma gamma
Andrzej Czarnecki and Kirill Melnikov
We compute the O(alpha_s^2) correction to the decay rate eta_c --> gamma
gamma and discuss its implications for precision quarkonium physics. We study
the suitability of the ratio Gamma(J/psi --> e+e-)/Gamma(eta_c --> gamma
gamma), in which the non-perturbative or soft effects cancel at
O(alpha_s^{0,1}), for extracting fundamental parameters of QCD at low energies.
We show that the QCD-based theory of charmonia is not capable of predicting
this ratio with any degree of confidence.
SPIRES or
http://arXiv.org/abs/hep-ph/0109054
Production of a pion pair in semileptonic decay of $J/\Psi$, $\Upsilon$ and $B_c$
J. P. Ma (ITP), Jia-Sheng Xu (CCAST & Itp)
We study the semileptonic decay of $J/\Psi$, $\Upsilon$ and $B_c$ into two
pions in the two kinematic regions. One is specified by that the two pions have
large momenta, but have a small invariant mass. Another is specified by that
the two pions have small momenta. In both cases we find that in the heavy quark
limit the decay amplitude takes a factorized form, in which the nonperturbative
effect related to heavy meson is represented by a NRQCD matrix element. The
nonperturbative effects related to the two pions are represented by some
universal functions characterizing the conversion of gluons into the pions.
Using models for these universal functions and chiral perturbative theory we
are able to obtain numerical predictions for the semileptonic decays into two
pions. Our numerical results show that the semileptonic decay of $\jpsi$ into
two pions is at order of $10^{-5}$ with reasonable cuts and can be observed at
BES II and the proposed BES III and CLEO-C. For other decays the branching
ratio may be too small to be measured.
SPIRES or
http://arXiv.org/abs/hep-ph/0109055
Vector meson masses in hot nuclear matter : the effect of quantum corrections
Amruta Mishra, Jitendra C. Parikh, Walter Greiner
The medium modification of vector meson masses is studied taking into account
the quantum correction effects for the hot and dense hadronic matter. In the
framework of Quantum Hadrodynamics, the quantum corrections from the baryon and
scalar meson sectors were earlier computed using a nonperturbative variational
approach through a realignment of the ground state with baryon-antibaryon and
sigma meson condensates. The effect of such corrections was seen to lead to a
softer equation of state giving rise to a lower value for the compressibility
and, an increase in the in-medium baryonic masses than would be reached when
such quantum effects are not taken into account. These quantum corrections
arising from the scalar meson sector result in an increase in the masses of the
vector mesons in the hot and dense matter, as compared to the situation when
only the vacuum polarisation effects from the baryonic sector are taken into
account.
SPIRES or
http://arXiv.org/abs/nucl-th/0108035
SPIRES or
www
New predictions for inclusive heavy-quarkonium P-wave decays
N. Brambilla, D. Eiras, A. Pineda, J. Soto, A. Vairo
We show that some NRQCD colour-octet matrix elements can be written in terms
of (derivatives of) wave functions at the origin and non-perturbative universal
constants once the factorization between the soft and ultrasoft scale is
achieved by using an effective field theory where only ultrasoft degrees of
freedom are kept as dynamical entities. This allows us to derive a new set of
relations between inclusive heavy-quarkonium P-wave decays into light hadrons
with different principal quantum number and with different heavy flavour. In
particular, we can estimate the branching ratios of bottomonium P-wave states
by using charmonium data.
SPIRES or
http://arXiv.org/abs/hep-ph/0109130
$J/\psi$ suppression in Pb+Pb collisions, a conventional description
A. K. Chaudhuri (VECC, Calcutta)
We have analyzed the latest NA50 data on $J/\psi$ suppression in Pb + Pb
collisions. $J/\psi$ production is assumed to be a two step process, (i)
formation of $c\bar{c}$ pair, which is accurately calculable in QCD and (ii)
formation of $J/\psi$ meson from the $c\bar{c}$ pair, which can be conveniently
parameterized. In a pA/AA collision, the as the $c\bar{c}$ pair pass through
the nuclear medium, it gain relative square momentum at the rate of
$\epsilon^2$ per unit path length. As a result, some of the $c\bar{c}$ pairs
can gain enough momentum to cross the threshold to become an open charm meson,
leading to suppression in pA/AA collisions. The parameters of the model were
fixed from experimental data on the total $J/\psi$ cross section as a function
of effective nuclear length. The model without any free parameter, give
excellent description of NA50 data on $E_T$ dependence of $J/\psi$ to Drell-Yan
ratio. The model was applied to predict the $E_T$ dependence of $J/\psi$ at
RHIC energy. Much larger suppression of $J/\psi$, in agreement with other model
calculations are predicted.
SPIRES or
http://arXiv.org/abs/hep-ph/0109141
Photoproduction of Heavy Quarkonia
B. Jaeger (Inst. Theor. Physics, Univ. Regensburg) and W. Schweiger
We investigate the reaction gamma+p -> V+p, with V denoting a Phi or a J/Psi
meson, within the scope of perturbative QCD, treating the proton as a
quark-diquark system. Our predictions extrapolate the existing forward
differential cross-section data into the few-GeV momentum-transfer region. In
case of the J/Psi reasonable results are only obtained by properly taking into
account its mass in the perturbative calculation of the hard-scattering
amplitude.
SPIRES or
http://arXiv.org/abs/hep-ph/0109144
Diffractive charm photoproduction at HERA ep-collider
A. V. Berezhnoy, V. V. Kiselev, I. A. Korzhavina, A. K. Likhoded
The cross section of the $D^*$-meson diffractive photoproduction at the HERA
collider has been calculated in the framework of perturbatively motivated model
for the different kinematic regions. The camparison between the different
Pomeron models has been performed.
SPIRES or
http://arXiv.org/abs/hep-ph/0109164
On the intrinsic charm and the recombination mechanisms in charm hadron production
J.C. Anjos, J. Magnin, G. Herrera
We study $\Lambda_c^\pm$ production in $pN$ and $\pi^-N$ interactions. Recent
experimental data from the SELEX and E791 Collaborations at FNAL provide
important information on the production mechanism of charm hadrons. In
particular, the production of the $\Lambda_c$ baryon provides a good test of
the intrinsic charm and the recombination mechanisms, which have been proposed
to explain the so called leading particle effects.
SPIRES or
http://arXiv.org/abs/hep-ph/0109185
Aspects of Charmonium Physics
S.F. Tuan
I review possible resolution of the $J/\psi (\psi^{\prime}) \to \rho-\pi$
puzzle based on two inputs: the relative phase between the one- photon and the
gluonic decay amplitudes, and a possible hadronic excess in the inclusive
nonelectromagnetic decay rate of $\psi^{\prime}$. The status of a universal
large phase here is examined for its meaning and implications (including those
for B-physics). Since the future of tau/charm facility(s) are again under
consideration together with a future anti-proton facility at GSI, I propose to
extend my review to include a broader discussion of charmonium physics.
Outstanding questions like the status of the $^{1}P_{1}$ state of charmonium,
measuring $D^{0}-\bar D^{0}$ mixing and relative strong phases, status of
molecular P(S) - wave charmonia will also be discussed amongst others.
SPIRES or
http://arXiv.org/abs/hep-ph/0109187
Heavy Flavour Physics at HERA - a Survey
P. J. Bussey
At the HERA collider at DESY, high energy electron and positron beams
interact with proton beams. A review is presented of the variety of ways in
which these collisions produce final states containing charm and beauty quarks.
SPIRES or
http://arXiv.org/abs/hep-ph/0109254
Intrinsic Charm Flavor and Helicity Content in the Proton
Xiaotong Song (Univ. of Virginia)
Contributions to the quark flavor and spin observables from the intrinsic
charm in the proton are discussed in the SU(4) quark meson fluctuation model.
Result suggests that the probability of finding the intrinsic charm in the
proton is less than 1%. The intrinsic charm helicity is small and negative,
$\Delta c \simeq -(0.003\sim 0.015)$. The fraction of the total quark helicity
carried by the intrinsic charm is less than 2%. A detail comparison of the
quark flavor and spin observables with data and other models or analyses is
given.
SPIRES or
http://arXiv.org/abs/hep-ph/0109289
Relative phase between the three-gluon and one-photon amplitudes of the J/psi decays
N.N. Achasov (Sobolev Institute for Mathematics SB RAS, Novosibirsk)
It is shown that the study of the \omega-\rho interference pattern in the
J/psi -> (rho+omega)eta -> pi+pi-eta decay provides evidence for the large
(nearly 90 degrees) relative phase between the isovector one-photon and
three-gluon decay amplitudes.
SPIRES or
http://arXiv.org/abs/hep-ph/0110057
Dissociation of a Heavy Quarkonium at High Temperatures
Cheuk-Yin Wong (ORNL)
We examine three different ways a heavy quarkonium can dissociate at high
temperatures. The heavy quarkonium can dissociate spontaneously when it becomes
unbound at a temperature above its dissociation temperature. Following the
recent work of Digal, Petreczsy, and Satz, we calculate the dissociation
temperatures of heavy quarkonia taking into account the angular momentum
selection rules and using a temperature-dependent potential inferred from
lattice gauge calculations. We find that the selection rules change the
dissociation temperatures substantially for charmonia but only slightly for
bottomia. A quarkonium system in thermal equilibrium with the medium can
dissociate by evaporation. The fraction of quarkonium lying above the
dissociation threshold increases as temperature increases. A quarkonium can
also dissociate by colliding with light hadrons. We evaluate the cross sections
for the dissociation of J/psi and Upsilon in collision with pion as a function
of the temperature of the hadron medium, using the quark-interchange model of
Barnes and Swanson. We find that as the temperature increases, the threshold
energy decreases and the dissociation cross section increases.
SPIRES or
http://arXiv.org/abs/nucl-th/0110004
Non-perturbative gluons in diffractive photo-production of J/Psi
M. B. Gay Ducati, Werner K. Sauter
The modifications induced in the calculation of the cross section of the
diffractive process gamma gamma -> J/Psi J/Psi when the gluon propagator is
changed are analyzed. Instead of the usual perturbative gluon propagator,
alternative forms obtained using non-perturbative methods like Dyson-Schwinger
equations are used to consider in a more consistent way the contributions of
the infrared region. The result shows a reduction in the differential
cross-section for low momentum transfer once compared with the perturbative
result, to be confirmed with future experimental results from TESLA.
SPIRES or
http://arXiv.org/abs/hep-ph/0110162
Parity and Time Reversal in J/Psi Decay
L. Clavelli, T. Gajdosik, and I. Perevalova (University of Alabama)
With the prospect of large numbers of J/Psi decay events becoming available
in the near future, it is interesting to search for symmetry violating effects
as probes of new physics and tests of the standard model. J/Psi decay events
could provide the first observation of weak effects in otherwise strongly
decaying particles. We calculate a T odd asymmetry in the J/Psi decay into
photon plus lepton pair due to Z boson exchange. Extensions to hadronic final
states are also discussed.
SPIRES or
http://arXiv.org/abs/hep-ph/0110076
Prospects for probing the gluon density in protons using heavy quarkonium hadroproduction
J.L. Domenech-Garret, M.A. Sanchis-Lozano and S. Wolf (Valencia
We examine carefully bottomonia hadroproduction in proton colliders,
especially focusing on the LHC, as a way of probing the gluon density in
protons. To this end we develop some previous work, getting quantitative
predictions and concluding that our proposal can be useful to perform
consistency checks of the parameterization sets of different parton
distribution functions.
SPIRES or
http://arXiv.org/abs/hep-ph/0110085
The charm quark's mass in quenched QCD
Juri Rolf, Stefan Sint
We present our preliminary result for the charmed quark mass, which follows
from taking the D_s and K meson masses from experiment and r0=0.5 fm (or,
equivalently F_K=160 MeV) to set the scale. For the renormalization group
invariant quark mass we obtain M_c = 1684(64) MeV, which translates to
m_c(m_c)= 1314 (40)(20)(7) MeV for the running mass in the MSbar scheme.
Renormalization is treated non-perturbatively, and the continuum limit has been
taken, so that the only uncontrolled systematic error consists in the use of
the quenched approximation.
SPIRES or
http://arXiv.org/abs/hep-ph/0110139
Next-to-leading-log renormalization-group running in heavy-quarkonium creation and annihilation
Antonio Pineda
In the framework of potential NRQCD, we obtain the next-to-leading-log
renormalization-group running of the matching coefficients for the heavy
quarkonium production currents near threshold. This allows to obtain S-wave
heavy-quarkonium production/annihilation observables with next-to-leading-log
accuracy within perturbative QCD. In particular, we give expressions for the
decays of heavy quarkonium to e^+e^- and to two photons.
SPIRES or
http://arXiv.org/abs/hep-ph/0110216
Momentum Transfer Dependence of the Differential Cross Section for $J/\psi$ Production
E. Gotsman (Tel-Aviv U.), E. Levin (Tel-Aviv U.), U. Maor (Tel-Aviv
We discuss the $\abst$ dependence of
$J/\psi$ production in the region of $0<\abst\lsim M^2_{\psi}$. The forward
slope of the elastic differential cross section is calculated assuming a
dipole-type dependence for the gluon ladder-proton form factor. The $\abst$
dependence of $d\sigma/dt$ is obtained using DGLAP evolution both for the
elastic channel at low $\abst$ and for the inelastic channel at large values of
$\abst$, up to $\abst\simeq M^2_{\psi}$. Results are presented and compared
with the relevant experimental data.
SPIRES or
http://arXiv.org/abs/hep-ph/0110256
Gluonic effects in vector meson photoproduction at large momentum transfers
N.I.Kochelev and V.Vento
The gluonic pole has been instrumental in explaining the mass of the
$\eta^{\prime}$ and providing a plausible explanation for solving the spin
crisis. We show that it also plays an important role in the description of the
photoproduction of vector mesons at high momentum transfers at JLab energies.
SPIRES or
http://arXiv.org/abs/hep-ph/0110268
J/psi Enhancement in Peripheral Pb+Pb Collisions at SPS
A.P. Kostyuk, M.I. Gorenstein, H. Stoecker, and W. Greiner
Production of J/psi-mesons in heavy ion collisions is considered within the
statistical coalescence model. The charmed quark-antiquark pairs are assumed to
be created at the initial stage of the reaction and their number is conserved
during the evolution of the system. At the hadronization stage, the charmed
(anti)quarks are distributed among open and hidden charm hadrons in accordance
with the prescriptions of the statistical mechanics. The model is in excellent
agreement with the experimental data for Pb+Pb collisions in a wide centrality
range, including the so called "anomalous" suppression domain. For the
peripheral collisions, however, the model predicts enhanced J/psi production
with respect to the "normal" nuclear suppression curve.
SPIRES or
http://arXiv.org/abs/hep-ph/0110269
Leptoproduction of Polarized Vector Mesons
B. Postler (Wuppertal Univ.)
We present a status report on a study of vector meson leptoproduction for the
HERA energy range on the basis of the generalized handbag approach. In contrast
to the leading twist approach transverse degrees of freedom as well as Sudakov
suppressions are taken into account in the subprocess. First results for the
cross section for photoproduction of longitudinally polarized rho-mesons are
found to be in fair agreement with experiment.
SPIRES or
http://arXiv.org/abs/hep-ph/0110271
Heavy quark production at HERA in k_t factorization supplemented with CCFM evolution
H. Jung (Physics Department, Lund University, Sweden)
The application of k_t - factorization, supplemented with the CCFM small-x
evolution equation, to heavy quark production is discussed. Differential cross
sections of b-b_bar production and also inelastic J/psi production as measured
at HERA are compared to the hadron level CCFM Monte Carlo generator CASCADE,
using the unintegrated gluon density obtained within the CCFM evolution
approach from a fit to HERA F_2 data.
SPIRES or
http://arXiv.org/abs/hep-ph/0110345
Renormalization group improvement of the NRQCD Lagrangian and heavy quarkonium spectrum
Antonio Pineda
We complete the leading-log renormalization group scaling of the NRQCD
Lagrangian at $O(1/m^2)$. The next-to-next-to-leading-log renormalization group
scaling of the potential NRQCD Lagrangian (as far as the singlet is concerned)
is also obtained in the situation $m\alpha_s \gg \Lambda_{QCD}$. As a
by-product, we obtain the heavy quarkonium spectrum with the same accuracy in
the situation $m\alpha_s^2 \simg \Lambda_{QCD}$. When $\Lambda_{QCD} \ll
m\alpha_s^2$, this is equivalent to obtain the whole set of
$O(m\alpha_s^{(n+4)} \ln^n \alpha_s)$ terms in the heavy quarkonium spectrum.
The implications of our results in the non-perturbative situation $m\alpha_s
\sim \Lambda_{QCD}$ are also mentioned.
SPIRES or
http://arXiv.org/abs/hep-ph/0109117
Discovery potential for New Physics in view of the RHIC-Spin upgrade
P. Taxil and J.-M. Virey
In view of a possible upgrade of the RHIC-Spin program at BNL, concerning
both the machine and the detectors, we give some predictions concerning the
potentialities of New Physics detection with polarized proton beams. We focus
on parity-violating asymmetries in one-jet production due to contact terms or
to a new leptophobic neutral gauge boson. We comment on the main uncertainties
and we compare with unpolarized searches at Tevatron.
SPIRES or
http://arXiv.org/abs/hep-ph/0109094
A Variational Fock-Space Treatment of Quarkonium
L. Di Leo and J. W. Darewych (York University, Toronto, Canada)
The variational method and the Hamiltonian formalism of QCD are used to
derive relativistic, momentum space integral equations for a quark-antiquark
system with an arbitrary number of gluons present. As a first step, the
resulting infinite chain of coupled equations is solved in the nonrelativistic
limit by an approximate decoupling method. Comparison with experiment allows us
to fix the quark mass and coupling constant, allowing for the calculation of
the spectra of massive systems such as charmonium and bottomonium. Studying the
results with and without the nonAbelian terms, we find that the presence of the
nonAbelian factors yields better agreement with the experimental spectra.
SPIRES or
http://arXiv.org/abs/hep-ph/0010127
Power counting and effective field theory for charmonium
Sean Fleming (1), Adam K. Leibovich (2) and I. Z. Rothstein (1) ((1)
We hypothesize that the correct power counting for charmonia is in the
parameter Lambda_QCD/m_c, but is not based purely on dimensional analysis (as
is HQET). This power counting leads to predictions which differ from those
resulting from the usual velocity power counting rules of NRQCD. In particular,
we show that while Lambda_QCD/m_c power counting preserves the empirically
verified predictions of spin symmetry in decays, it also leads to new
predictions which include: A hierarchy between spin singlet and triplet octet
matrix elements in the J/psi system. A quenching of the net polarization in
production at large transverse momentum. No end point enhancement in radiative
decays. We discuss explicit tests which can differentiate between the
traditional and new theories of NRQCD.
SPIRES or
http://arXiv.org/abs/hep-ph/0012062
Integral characteristics of bremsstrahlung and pair photoproduction in a medium
V. N. Baier and V. M. Katkov
The bremsstrahlung of an electron and $e^{-}e^{+}$-pair creation by a photon
in a medium is considered in high-energy region, where influence of the
multiple scattering on the processes (the Landau-Pomeranchuk-Migdal (LPM)
effect) becomes essential. The integral characteristics: the radiation length
and the total probability of radiation and pair photoproduction are analyzed
under influence of the LPM effect.
SPIRES or
http://arXiv.org/abs/hep-ph/0012064