Working Group 3

Extraction of the Unitarity Angle GAMMA

Theorist Convener:

Robert Fleischer
phone: +41 22 767 2459, fax: +41 22 767 3850
e-mail: Robert.Fleischer@cern.ch

Experimentalist Conveners:

Paul Dauncey
phone (441235)-445-261, fax (441235)-446-733;
e-mail: P.Dauncey@v2.rl.ac.uk

Livio Lanceri
phone (+3940)-3756260, fax (+3940)-3756258;
e-mail: lanceri@trieste.infn.it


On this page:
  • Introduction
  • Rome meeting, November 11-14, 1996
  • Princeton meeting, March 17-20, 1997
  • Orsay meeting, June 16-19, 1997
  • Caltech meeting, September 22-24, 1997
  • Gamma chapter layout
  • Gamma chapter draft
  • References
    •

    Introduction

    The measurement of the Unitarity Angle GAMMA is relevant for a complete test of the CKM scheme. This measurement will be difficult, but it is certainly stimulating and is worth a serious study. In Working Group 3, we will consider the following issues:
  • Why do we need to measure the CP angle GAMMA ?
  • What methods could be used in principle to measure GAMMA ?
  • Bs--> rho Ks
  • Standard approach (asymmetry from mixing-decay interference)
  • Difficulties: Bs, very small rate, penguins
    •
  • Bs--> Ds K, D phi
  • "Theoretically clean", no penguins
  • Difficulties: Bs, time dependences
    •
  • Bu--> D K and Bd--> D K* "triangles"
  • Tagged or self-tagging decays, no time measurement, no Bs
  • "Theoretically clean", but: rather low rates
    •
  • B--> pi pi, K pi, eta K
  • SU(3) "triangles" and "quadrangles"
  • Difficulties: ew penguins, SU(3) breaking, factorization...
    •
  • Bd--> D Ks, Bs--> D phi
  • Bs width difference: untagged Bs decays
    •
  • Are the proposed methods theoretically sound ?
  • Underlying dynamical assumptions ? (factorization, neglected amplitudes, strong phases, penguins etc.)
  • Theoretical uncertainties ? (quantitative!)
  • Possible experimental tests of assumptions and of models ?
    •
  • Are the theoretically sound methods experimentally feasible ?
  • Review all the relevant rate estimates
  • When a time measurement is needed, is it feasible?
  • Roughly guess efficiencies and backgrounds
    •
  • For the most promising methods (for instance B--> D K triangles) proceed to a more detailed quantitative analysis
  • ASLUND efficiency and background studies
  • Evaluate the most efficient methods (fits) to extract the information from several rate measurements (triangles and quadrangles)
    •
  • A relevant practical point is to assess if there is a physics case for running at the Upsilon(5s) producing Bs
  • Summary of the accessible physics, luminosity requirements
  • PEP-II machine problems and requirements
  • Detector problems and requirements
    •
  • Compare BaBar sensitivities with our competitors', under reasonable assumptions on the integrated luminosity (specially for this part of the program, going quickly to high luminosity is essential)
  • CESR/CLEO
  • HERA-B
  • CDF
  • LHC-B and the other LHC experiments
    •
    • There are several items that should be discussed in the joint sessions with other working groups; for each joint meeting we plan to present a short report listing and preliminarly discussing the areas of common interest and possible ways of sharing the work:
  • with Group 1 (CP Violation in Neutral B Meson Decays):
  • Tagging, when relevant;
  • Reconstruction efficiencies for channels involving D0
  • Fitting methods: best ways of extracting information from combined rates measurements ("triangles", "quadrangles")
    •
  • with Group 2 (Direct CP Violation and Penguins):
  • Evaluation of the importance of penguins in the proposed methods
  • Ways of isolating/eliminating the penguin contributions, in particular in the analysis based on the SU(3) symmetry
  • Efficiencies and background studies in channels such as K0 pi+, K+ pi0, pi+ pi0 (SU(3) analysis) if we decide they are relevant
  • Fitting methods: best ways of extracting information from combined rates measurements ("triangles", "quadrangles")
    •
  • with Group 6 (B decay models):
  • Review of the proposed decay channels for Gamma extraction
  • Critical examination of the assumptions and model dependences of the proposed methods from the point of view of the implicitly or explicitely assumed decay models
    •
  • with Group 8 (Tau, Charm and Two-photon Physics):
  • We might marginally share some aspects of efficiency studies for states involving D mesons
    •
  • with Group 9 (Overall Unitarity Triangle Sensitivity):
  • What is the impact of an independent measurement of Gamma on the overall sensitivity ?
  • At what level of sensitivity on Gamma the measurement starts giving useful information?
    •

    • Rome meeting, November 11-14, 1996

  • The working group was joined by:
  • Mario Posocco
  • Ezio Torassa
  • Cristiano Rastelli
    •
  • The proposed approaches to measure Gamma were reviewed from the theoretical point of view (R.Fleischer, transparencies available) and from the experimental point of view (L.Lanceri); preliminary work in BaBar on DK triangles was reviewed by A.Snyder.
  • As a result of this review:
  • the most promising approach appears to be the analysis based on B -> D K triangles (M.Gronau and D.Wyler, PL B265 (1991) 172, and I.Dunietz, PL B270 (1991) 75); the experimental work of WG#3 till Princeton will be mainly concentrated on these channels, to estimate the sensitivity of BaBar corresponding to an integrated luminosity of 100 fb-1;
  • among the methods based on the SU(3) flavor symmetry, one should start investigating that suggested by R.F., PLB365 (1996) 399; due to lack of manpower, the estimation of the BaBar sensitivity will rely on efficiency and background estimates in pi K and pi pi final states by other working groups (WG#2);
  • other clean methods are based on measurements of time dependences in B_s decays; basic difficulties are running at the upsilon(5s) and resolving the B_s oscillations, expected to be very fast (x_s > 14 from LEP measurements). The x_s reach of BaBar will be cross-checked (earlier work exists) and theoretically the possibility of using untagged B_s will be studied.
    •

    • Princeton meeting, March 17-20, 1997

  • P.Dauncey, R.Fleischer, L.Lanceri (conveners),
  • Amol Dighe
  • David Atwood
  • Isi Dunietz
  • Mario Posocco
  • Iain Scott
    •

    The first parallel session was centered on two presentations:

  • Paul Dauncey presented a detailed analysis, based on Aslund plus Beta, of the reconstruction efficiencies of all relevant combinations of DK final states for the measurement of Gamma based on the Gronau-Wyler approach of B to DK "triangles". The reconstructed channels included D^0 decaying to charged and neutral kaons and pions (up to four particles) and D*^0 decaying to D^0 with both pi^0 and single photon emission. A first rough estimate of backgrounds was also given, indicating that similar studies by Belle look rather optimistic.
  • Livio Lanceri presented some preliminary plots and efficiencies on the reconstruction of the simplest DK final states (Aslund + Beta) and a study of the error propagation in measuring Gamma from DK triangles, trying different assumptions on the branching ratios of colour-suppressed channels and strong phases, and comparing the results with those obtained by Belle (this work was done in Trieste with G.Vuagnin and C.Rastelli). Also some preliminary work on the Atwood-Dunietz-Soni method was discussed.
    •

    During the joint session with WG#12 there were three presentations relevant for the determination of Gamma:

  • Isi Dunietz and David Atwood presented the interesting proposal by Atwood-Dunietz-Soni (hep-ph/9612433) to modify the recipe by Gronau and Wyler by considering doubly Cabibbo suppressed decays of D^0 and some preliminary estimates on the sensitivity of the method.
  • Amol Dighe discussed some ideas based on the SU(3) symmetry.
    •

    During the last parallel session several items were discussed:

  • The implications of the ADS method were discussed, in particular the ML function used by Atwood for the sensitivity estimates and the Dalitz analysis needed for three-body decays of D^0.
  • Robert Fleischer recalled his SU(3) method to determine Gamma (R.F., PLB365 (1996) 399).
  • Iain Scott presented some efficiencies and background rejection estimates for pipi and piK channels, needed in determinations of Gamma based on SU(3).
  • The summary to be presented in the final session by Paul Dauncey was discussed. In particular, the range of branching ratios to be assumed for the uncertain colour suppressed channels were agreed upon.
  • The layout of the chapter on Gamma was discussed (see following section).
    •  Finally, the priorities for the work to be done till the Orsay meeting were discussed:
  • The highest priority job is to better understand the background contamination and rejection in the B -> DK analysis, and to take into account the ADS proposals in the evaluation of sensitivity.
  • The sensitivity of SU(3) method can be roughly evaluated from efficiencies and backgrounds estimated by WG12. If promising, more work will be dedicated to this analyisis.
  • For the time being, all work on Bs at the Upsilon(5s) is in stand-by due to lack of manpower.
    •

    Orsay meeting, June 16-19, 1997

    Preliminary agenda:
  • Monday, June 16, 1997:
  • Morning: Plenary Session, Main Auditorium
  • Afternoon: WG3 Parallel Session, Room 166, Bldg 200
  • 14:30: R.Fleischer/P.Dauncey/L.Lanceri: Introduction: theoretical and experimental status of the WG. Review of the work done since Princeton and of the priorities of the WG.
  • 16:30: Open discussion. Work to be done: volunteers? New theoretical/experimental ideas? Chapter outline review and sharing of the work.
    •
  • Tuesday, June 17, 1997:
  • Morning:
  • 9:00:
  • Joint Session (WG 12a, 12b, 3, 9), Main Auditorium
  • R.Fleischer: constraining the CKM angle gamma and penguin contributions through combined B->pi K Branching ratios
    •
  • 11:00:
  • Mini-Plenary Experimental Session, Main Auditorium
    •
  • Afternoon: WG3 Parallel Session, Room 166, Bldg 200
  • 14:30: analyses based on SU(3)
  • F.Wuerthwein: B->pi K measurements in CLEO
  • I.Scott (to be confirmed): B->pi K and B->pi pi analysis
  • F.Ferroni/L.Cavoto: improved B->pipi cuts performance
  • L.Lanceri: gamma sensitivity estimates
    •
  • Wednesday, June 18, 1997:
  • Morning:
  • 9:00:
  • Joint Session (WG 12a, 12b, 3, 5, 6), Main Auditorium
  • 11:00:
  • Mini-Plenary Experimental Session, Main Auditorium
    •
  • Afternoon: WG3 Parallel Session, Room 166, Bldg 200
  • 14:30: Review of the new results relevant for Gamma determination. Discussion on the presentation of the Group 3 summary.
  • 16:30: To-do list, new priorities for further experimental work, chapter writing.
    •

    • CalTech meeting, June 16-19, 1997

    The meeting was mainly devoted to editing and discussions on how to compute sensitivities when Gamma is measured using triangular relations between amplitudes. An interesting method to extract sin(2*beta+gamma) was presented by the UCSB group. It is based on the measurement of an asymmetry in B_d to D*+- pi-+. The possibility of obtaining an inclusive reconstruction with high efficiency was demonstrated on CLEO data.

    Gamma chapter layout

    Including rough projected pagecount. Authors are listed by initials, where PD = Paul Dauncey, RF = Robert Fleischer, LL = Livio Lanceri
  • 1) Motivation for Measuring Gamma (2 pages)
    Mainly theory. (RF)
  • 2) Overview of Gamma Methods/Strategies and Outline of Chapter (1 page)
    Mainly a list of methods. Some discussion of relative theoretical cleanliness. (RF)
  • 3) B->DK Method
    a) Theory of method (5 pages). (RF)
    b) Experimental results (10 pages). (PD, LL)
  • 4) SU(3) Methods
    a) Theory of method (10 pages). This will include some discussion on geometrical constructions which can also be applied to angle Alphameasurements and so may overlap WG12A. (RF)
    b) Experimental results (5 pages). Some overlap with results quoted in the WG12A chapter. (PD, LL)
  • 5) Upsilon(5s) Methods
    a) Theory of method (5 pages). (RF)
    b) Experimental results (5 pages). There may be overlap with WG7 for discussion of x_s reach and delta-Gamma_s measurements. Should there be a separate Upsilon(5s) chapter in the report? (PD, LL)
  • 6) Summary of Results and Overall Gamma Reach (2 pages)
    Collection of the above results. (PD, LL)
    •  Total page count = 45 pages

    Gamma chapter draft

    Click here for the "Gamma chapter draft" (postscript) of the BaBar Physics Book.

    Preliminary list of references

    (see updated list in the draft)

    Basic References and Review Papers

    CP Violation, Yosef Nir; SLAC-PUB-5874 WIS-92/67/Sep-PH. Proc. XX SLAC Summer Institute on Particle Physics, July 1992, SLAC-Report-412

    Theory of CP Violation in B Decays, Y.Nir and H.R.Quinn, in "B Decays", Revised 2nd Edition, ed. by S.Stone, World Scientific, 1994, p.520.

    CP Violation with Additional B Decays, I.Dunietz, ibidem, p.550.

    In Pursuit of Gamma, R.Aleksan, B.Kayser, D.London, talk at the Workshop on B Physics at Hadron Accelerators, Snowmass, Colorado, June 21-July 2, 1993, hep-ph/9312338.

    CP Violation in the B System, R.Fleischer, Talk at the III German-Russian Workshop on Heavy Quark Physics, Dubna, Russia, May 20-22, 1966, hep-ph/9606469.

    CP Violation and the Role of Electroweak Penguins in Non-leptonic B Decays, R.Fleischer, hep-ph/9612446, December 1996.

    Quark Mixing, CP Violation and Rare Decays After the Top Quark Discovery, A.J.Buras and R.Fleischer, hep-ph/9704376, April 1997.

    Experimental Sensitivity Studies

    Can we measure Gamma on the Upsilon(4s) with B-->DK* decays ?, A.Snyder; BaBar-Note #80 (3/18/92).

    B^+-->D^0 K^+ at the SLAC B-factory, A.Snyder; BaBar-Note #84 (6/8/92).

    BELLE Progress Report 1995 April - 1996 March, The Belle Collaboration, KEK Progress Report 96-1 H, March 1996, p.138.

    Letter of Intent, The LHB Collaboration, CERN/LHCC/93-45 LHCC/I5, p.10-12.

    The CESR-CLEO Program, K.Berkelman, CLNS 96/1398.

    Theoretically clean strategies: B-->D K triangles

    On determining a weak phase from charged B decay asymmetries, M. Gronau and D.Wyler, Phys. Lett. B265 (1991) 172.

    CP violation with self-tagging Bd modes , I.Dunietz, Phys. Lett. B270 (1991) 75.

    Enhanced CP Violation with B -> KD^0(D^0.bar) Modes and Extraction of the CKM Angle Gamma, D.Atwood, I.Dunietz, A.Soni, hep-ph/9612433.

    Bs decays caused by b -> c u.bar s quark-level transitions

    How to determine all the angles of the unitarity triangle from bd -> D Ks and Bs -> D phi, M.Gronau and D.London, Phys. Lett. B253 (1991) 483..

    Determining the CP-violating phase gamma, R.Aleksan, I.Dunietz and B.Kayser, Z. Phys. C54 (1992) 653.

    CP violation and the CKM angle Gamma from angular distributions of untagged Bs decays governed by b.bar -> c.bar u s.bar, R.Fleischer and I.Dunietz, hep-ph/9605221.

    Strategies using the SU(3) flavour symmetry of strong interactions

    Weak Coupling Phase from Decays of charged B mesons to pi K and pi pi , M.Gronau, J.L.Rosner, D.London, Phys. Rev. Lett. 73 (1994) 21.

    Decays of B mesons to two light pseudoscalars, M.Gronau, O.F.Hernandez, D.London and J.L.Rosner, Phys. Rev. D50 (1994) 4529.

    Isospin Structure of Penguin Diagrams and Their Consequences in B Meson Physics, N.G.Deshpande and X.He, Phys. Rev. Lett. 74 (1995) 26.

    Decays of B mesons to two pseudoscalars in broken SU(3) symmetry, M.Gronau, O.F.Hernandez, D.London and J.L.Rosner, Phys. Rev. D52 (1995) 6356.

    Electroweak penguin diagrams and two-body B decays, M.Gronau, O.F.Hernandez, D.London and J.L.Rosner, Phys. Rev. D52 (1995) 6374.

    A method for Determining the CP violating Phase gamma, N.G.Deshpande and X.He, Phys. Rev. Lett. 75 (1995) 3064.

    Determining the CKM Unitarity Triangle from B Decays to Charged Pions and Kaons , M.Gronau and J.L.Rosner, Phys. Rev. Lett. 76 (1995)1200.

    Weak phases from B decays to kaons and charged pions, A.S.Dighe, M.Gronau and J.L.Rosner, Phys. Rev. D54 (1995) 3309.

    Determination of CKM phases through rigid polygons of flavor SU(3) amplitudes, A.S.Dighe, hep-ph/9509287.

    Amplitude relations for B decays involving eta and eta', A.S.Dighe, M.Gronau and J.L.Rosner, hep-ph/9509428.

    Determining the weak phase gamma from charged B decays, M.Gronau and J.L.Rosner, hep-ph/9509325.

    Strategies for Fixing the CKM-angle gamma and Obtaining Experimental Insights into the World of Electroweak Penguins, R.Fleischer, hep-ph/9509204.

    A study of some methods for measuring CKM CP violating phases, N.G.Deshpande, X.He and S.Ho, hep-ph/9511462.

    On measuring CP violating Phase gamma Using Neutral B Decays, N.G.Deshpande and S.Ho, hep-ph/9606235.

    Constraining the CKM Angle gamma and Penguin Contributions through combined B ---> PI K Branching Ratios. Robert Fleischer and Thomas Mannel, hep-ph/9704423.

    Strategies making use of the Bs width difference (untagged Bs decays)

    Bs mixing, CP violation, and extraction of CKM phases from untagged Bs data samples, I.Dunietz, Phys. Rev. D52 (1995) 3048.

    CP violation and CKM phases from angular distributions for Bs decays into admixtures of CP eigenstates, R.Fleischer and I.Dunietz, hep-ph/9605220.

    CP violation and the CKM angle gamma from angular distributions of untagged Bs decays governed by b.bar -> c.bar u s.bar, R.Fleischer and I.Dunietz, hep-ph/9509325.

    CP violation and CKM phases from time-dependences of untagged Bs decays, R.Fleischer, hep-ph/9609332.

    Other topics concerning running at the Upsilon(5s)

    PEP-II, An Asymmetric B Factory: Conceptual Design Report, SLAC-418.

    Precision on the x_s Measurement, F.Le Diberder, BaBar Note #49 (Aug.1990).

    The Dependence of Maximum x_s on Luminosity, J.E.Bartelt, BaBar Note #103 (May 1993).

    Miscellanea

    Enhancement of CP violation in B+- -> Ki+- D0 by resonant effects, D.Atwood, G.Eilam, M.Gronau and A.Soni, hep-ph/9409229.

    This page is maintained by Livio Lanceri: comments welcome!