Review of Top Cited HEP Articles
Reviewer is Michael Peskin, with earlier editions also available.
One of the most popular features of the SLAC SPIRES-HEP Literature database is the citation search, which identifies how many subsequent papers have cited a particular journal article or an e-print archive paper. Such a search can be used to identify influential contributions to high-energy physics and related fields. In this document, we present the articles which have received the most citations.
These lists reflect the standings in the SPIRES-HEP database as of December 31, 2003.
Here we present the list of the 50 articles from the SPIRES-HEP database that have collected the most citations in the calendar year 2003. We know of no better indicator of which are the "hot" topics today in high-energy physics and the related fields of astrophyiscs and nuclear physics that are covered by the database. In the remainder of this section, we will describe these 50 articles in groups corresponding to their subject matter. The comments on the beauty and the technical merit of these papers, as opposed to their quantifiable popularity, are the personal responsibility of the reviewer.
For the past two years, the SPIRES-HEP database has indexed the astro-ph and gr-qc eprint archives, as well as the hep-ex,ph,th and nucl-ph,th archives that cover particle and nuclear physics. We felt that this addition was warranted by the increasing interdependence of high-energy physics and astrophysics. As a consequence, many purely astrophysical topics, as well as topics in the interface region, are appearing on the topcite list. This is hardly a problem, but it requires one to go deeper into the list in order to obtain a fair coverage of the extended field that the database now surveys. Beginning this year, I will review the top 50 cited articles, treating high-energy and astrophysical topics on the same footing as best I can.
The number 1 cited article, with citation counts off the normal scale, is the Review of Particle Physics, compiled by the Particle Data Group (PDG). Together, all of the editions have collected 1702 citations in the past year. For better or worse, it has become a standard practice, especially in the theoretical literature, to cite this very useful compilation of data rather than the original experimental sources. The PDG does a service to the community which is more than just bibliographic. It produces well-thought-out averages and analyses of the data, making use of the opinions of leading experts. The PDG averages are intentionally conservative and are meant to reflect community consensus. I like to quote the PDG values for basic input quantities that I hope will not be controversial. For experimental values crucial to a given analysis, there is more to be learned by going back to the original sources. But you must judge whether this new information is signal or noise.
Over the past two years, beginning even before SPIRES started to index astrophysical papers, new experimental developments in cosmology have made a prominent appearance on the topcite list. It would have been remarkable if it were otherwise. In the past few years, experimental cosmology has made a historic transition from a field in which the largest issues were a matter of speculation to one whose global picture is finally known. During the past year, new measurements have determined the basic cosmological parameters quantitatively, and the era of precision measurement of these parameters is already in sight. Pieces of this information have come from many sources, and I will review them systematically in a moment. However, the biggest news of 2003 is the measurement of the whole panoply of cosmological observables through the fluctuations in the cosmic microwave background radiation. A new set of measurements of the microwave background from the dedicated Wilkinson Microwave Anisotropy Probe (WMAP) satellite was released in February, 2003. The papers of the WMAP collaboration immediately rocketed to the front of the topcites. Of the initial group of 12 papers by this collaboration, 4 appear on this year's topcite list. One of these (#2) recorded an amazing 812 citations in its first nine months. The papers that cite it range over the entire breadth of SPIRES' coverage, including works on quantum gravity, supersymmetry and high-energy physics model-building, neutrino physics, and astrophysical surveys.
At the beginning of the 1990's, cosmology was already in ferment, with the various cosmological measurements that were accumulating seeming to present contradictory pictures of the universe. To discuss this situation, it is convenient to present the energy density of the species j as Omega(j), the ratio of the observed energy density to the total energy density in an expanding but spatially flat universe. If the sum of these components, which I will call Omega, is less than 1, the universe bends outward as a hyperbolic surface; the the sum is greater than one, the spatial section of the universe is a sphere. Thus, Omega = 1 is often described as "the energy needed to close the universe".
From the early 1980's, measurements of mass on the largest scales, infered from the gravitational attraction of the elements of large clusters of galaxies, gave Omega(matter) in the range 10-40%. (For an early review of this topic, see, Peebles, Ap. J. 284, 439 (1984); for recent determinations, see Peacock et al. (2dF survey), astro-ph/0103143, Bahcall et al. (SDSS), astro-ph/0205490.) Of this mass, only a tiny fraction is accounted for by stars and luminous gas. One might have been tempted to say that the rest is composed of planets, rocks, and dark gas, but this possibility is excluded by consideration of the primordial synthesis of the light elements. The fractions of Helium and Deuterium in primordial gas is sensitive to the density of baryons present when the temperature of the universe was about 1 MeV. From this dependence, Hoyle, Fowler, and Wagoner concluded already before 1970 that Omega(baryon) < 10%. A modern analysis gives Omega(baryon) ~ 5%. For some time, it was thought that the remaining matter could be composed of heavy neutrinos. However, the current bound of about 1 eV on the mass of the electron neutrino, together with the determination from neutrino oscillations that neutrino mass differences are small, excludes this possibility. Thus, we require Omega ~ 20-30% in a new species of heavy particle not contained in the Standard Model of particle physics. This component of the cosmic mass density has been given the name "dark matter".
One of the guiding principles of modern cosmology is the theory of "inflation", the idea that the early history of the universe included a period of rapid expansion terminated by a phase transition in the vacuum of space-time. Inflation predicts Omega = 1. Though it might have been possible to reconcile the observations of the cosmic mass with Omega(matter) ~ 1 by choosing a small value of the Hubble constant, increasingly accurate measurements of the Hubble constant in the early 1990's threatened this argument. Very recently, the Hubble constant has been measured to high accuracy by a team that used the Hubble Space Telescope to determine the brightness of Cepheid variable stars in the local group and in the Virgo and Fornax clusters, to calibrate the cosmic distance scale out to a distance of 20 Mpc (#22). This would have set up a sharp contradiction with the theory of inflation, were it not for another remarkable set of cosmological data.
In 1998, the Supernova Cosmology Project (#4) and the Supernova Search Team (#11) reported observations of the cosmological expansion based on observations of distant type Ia supernovae, sources of approximately known brightness, discovered by novel automated methods. These groups were surprised to find that the expansion of the universe is accelerating, an observation that requires a component in the cosmic energy density which gives negative pressure. New forms of matter do not fit the profile. What is required instead is pure vacuum energy, a contribution to the cosmological constant or a field that can give effects similar to that of a cosmological constant. This component of the cosmic energy density has been given the name "dark energy". The supernovae observations did not give a sharp value for the density of dark energy, but they were flatly inconsistent with Omega(matter) = 1. For Omega(matter) ~ 30% as determined by large clusters of galaxies, the supernova data implied Omega ~ 70% in dark energy. This year's topcite list includes a leading review of dark energy and the cosmological constant by Peebles and Ratra (#43)--which I recommended in last year's report---and two of the original papers on the possibility of time-dependent dark energy ("quintessence") by Ratra and Peebles (#30) and Caldwell, Dave, and Steinhardt (#47).
The picture of the universe suggested by these pieces of data has now been brought into sharp focus by the new observations of the cosmic microwave background (CMB). The microwave background originates in the cosmological era of "recombination", actually the first combination of electrons and nuclei into neutral atoms. Before recombination, the universe was a plasma, after, it became transparent. The time of recombination is, by accident, close to the time when, as the universe cooled, the energy density in radiation decreased below the energy density in matter. Only in a universe dominated by non-relativistic matter is there an instability for matter to collapse under gravity. The fluctuations in the CMB actually show the sound waves in the cosmic plasma due to the first collapsing structures, the small enhancements of density that will eventually be the seeds of galaxies. The pattern of fluctuations has a prominent peak at angular sizes of about 10 mrad and further smaller peaks corresponding to the successive oscillations. The angular size of the first peak can be compared to expected physical size of the horizon at recombination. This comparison gives information on the shape of the light paths between that cosmic event and the present time. It tells us whether the universe is flat or postively or negatively curved. The height of this peak is sensitive to the density of baryons or Hydrogen at the era of recombination. The ratio of heights of successive peaks is sensitive to the ratio of the density of baryons to the total density of nonrelativistic matter. Thus, the CMB fluctuations give evidence on all of the pieces of the puzzle of the energy content of the universe--Omega, Omega(matter), and Omega(baryon). Useful references on the variation of the CMB fluctuation with cosmological parameters are Jungman et al, astro-ph/9512139, and Wayne Hu's web site http://background.uchicago.edu/~whu/physics/physics.html.
Over the past few years, results from lower-precision CMB observations have given evidence that Omega = 1 to about 10% accuracy. I have described the results of the CMB observations by the Boomerang experiment (#42) in previous editions of the topcites. The WMAP results (#2, #3, #21) bring the precision of this observation to about 2% accuracy, and also give high-accuracy deteminations of the components: Omega(baryon)= 4%, Omega(matter) = 26%. This is striking confirmation that we live in flat universe dominated today by dark energy.
I have noted already that Omega = 1 is a consequence of the theory of inflation. The WMAP data offers other sharp tests of the theory of inflation (#31). In inflationary cosmology, the primordial density fluctuations result from the quantum fluctuations of an massless scalar field under the influence of rapid cosmic expansion. In the ideal case, the resulting density fluctuations should be Gaussian with a scale-invariant spectrum. Both features are confirmed by the WMAP results. Detailed models of inflation predict small corrections to these qualitative features. Some models are already excluded due to the strength of the WMAP tests. One consequence of the new tests of inflation and the dramatic confirmation of the basic elements of this picture is that Alan Guth's original proposal of the inflationary universe has returned to the topcites at #29.
The importance of the CMB observations has brought onto the topcite list several papers that give important methodologies for these experiments. At #6, we find the paper of Schlegel, Finkbeiner, and Davis that gives detailed maps of dust emissions that provide a foreground to the CMB and to other astrophysical IR and microwave sources. These maps can be used to correct astrophysical data using a methodology described by Cardelli, Clayton, and Mathis (#23). The theory of the density oscillations at recombination is elegantly implemented for comparison to the CMB data in the code CMBFast, by Seljak and Zaldarriaga. The original paper on the numerical method used in CMBFast appears at #48. In addition, we find two important papers on cosmic large-scale structure. The influential paper of Navarro, Frenk, and White on numerical models of clustering and their parametrization appears at #19. The first results from what is currently the largest-scale galactic survey, the Sloan Digital Sky Survey, appear at #26 and #35. A paper of Landolt that gives standard stars for use in the photometric calibration of survey data appears at #40.
The last astrophysical paper on the topcite list is not connected to cosmology but comes from another domain. In 1989, Anders and Grevesse published what is now the standard review of element abundances in the sun (#44). The Anders-Grevesse abundances now give the reference values for determination of element abundances in distant stars and galaxies by the new X-ray observatories Chandra and XMM-Newton.
Neutrino physics received an extensive discussion in last year's topcite review, but a new entry this year calls for attention.
The last few years have seen remarkable progress in all aspects of the problem of neutrino mass, but especially in understanding the origin of the deficit of solar neutrinos originally observed (beginning in the 1960's) by the Homestake Mine experiment (#33). The observation of neutrino oscillations at higher energy by the Super-Kamiokande experiment (#14) gave impetus to the idea that the observed deficit of solar neutrinos was only an apparent one, caused by neutrinos changing their flavor between their source in the sun and their detection on earth. In the past two years, the SNO experiment has dramatically confirmed this idea. Using a water Cherenkov detector containing heavy water, the SNO collaboration measured the solar neutrino flux in three different ways, by charged-current neutrino scattering from Deuterium, from neutral-current scattering, and from neutrino-electron scattering (#12, #24). The cross section for neutral-current scattering from nuclei is independent of the neutrino flavor. The charged-current process occurs only for electron neutrinos. Neutrino-electron scattering obtains contributions from all species but it largest for electron neutrinos. Any two of these measurements allow one to solve for the separate solar neutrino fluxes in electron neutrinos and in muon and tau neutrinos; the third provides a cross-check. The result of the experiment was remarkable: The total flux of neutrinos from the sun agreed precisely with the prediction from solar models. However, a large part of this flux was seen as muon and tau neutrinos. Since the nuclear reactions in the sun produce only electron neutrinos, these results require nonzero neutrino masses and neutrino flavor mixing between the sun and the earth. An additional paper from SNO searches for an expected corrolary phenomenon, a day-night asymmetry in the solar neutrino signal; unfortunately, the effect is not yet statistically significant (#20).
To confirm this idea, and to pin down the parameters of the neutrino mass matrix, it would be desirable to observe this neutrino mixing in a purely terrestrial setting, using a known and human-controlled source of neutrinos. The new topcite paper by the KamLAND Collaboration does just that (#10). By filling the original Kamiokande detector with liquid scintillator, the KamLAND group created a detector that would be sensitive to electron antineutrinos from nuclear reactors and compared the neutrino signal in this detector to fluxes computed from the known energy output of reactors in Japan near the Kamioka site. They observed a significant deficit of neutrino events. This deficit and its dependence on anti-neutrino energy picked out a region in the space of neutrino mass versus mixing angle that had previously been proposed to fit the deficit of solar neutrinos. This striking concordance of results from astrophysical and terrestrial neutrino sources brings the solar neutrino problem from a mystery to an understood phenomenon that is now a target of increasingly precise measurements.
Unfortunately, very little progress has been made in the past few years in characterizing the original oscillation of atmospheric neutrinos discovered by Super-Kamiokande. The Super-Kamiokande paper does continue to excite interest and accumulate citations. With more than 2000 citations in SPIRES at the present time, this paper continues to be the most-cited experimental paper in the database. But we are still waiting for the next major step in characterizing the atmospheric oscillation. With luck (and funding), the MINOS long-baseline neutrino experiment should begin running in 2005 and should provide a sharp determination of the neutrino mass difference and mixing angle in the Super-Kamiokande region. It is still not known whether the Super-Kamiokande mixing involves only the muon and tau neutrinos or whether the electron neutrino is also involved. Oscillations of the electron neutrino at the atmospheric mass value is strongly constrained by the Chooz reactor experiment of the 1990's (#25), but new searches beyond the Chooz limit have not yet been undertaken. MINOS has some added sensitivity to electron neutrino mixing, but more likely the observation of this effect will require a dedicated experiment later in this decade.
For a more detailed survey of the experimental situation in neutrino physics, I again recommend the comprehensive paper of Gonzalez-Garcia and Nir in Reviews of Modern Physics (hep-ph/0202058).
Two theory papers relevant to neutrino mass appear for the first time on this year's topcite list, and both deserve some discussion, since they are cited in connection with the most fundamental issues of the origin of neutrino masses and mixings. First of all, who should receive credit for the idea of neutrino mixing? The Super-Kamiokande collaboration called the unitary matrix that parametrizes neutrino mixing the Maki-Nakagawa-Sakata (MNS) matrix, paying homage to the paper #49 which introduced lepton mixing for the first time. However, I do not recommend that people who choose this notation actually read the MNS paper. This paper is one of those early works on weak interactions that now seem hopelessly outdated because the authors could not make use of the full flavor symmetry of the Standard Model as we know it today. MNS were actually trying to explain Cabbibo mixing within the Sakata model of hadron structure, in which the mesons are bound states of SU(3) triplet baryons (p, n, lambda) and their antiparticles. Having no freedom in the hadron sector, they introduced mixing in the lepton sector. There is no question that Sakata deserves to have his name on this piece of fundamental physics, but I would prefer also to pay homage to the first person to write about neutrino mass (without mixing): Bruno Pontecorvo (Zh.Eskp.Teor.Fiz.33,549 (1957) and 34:247(1958)). So, please, call it the MNSP matrix.
Next, why are neutrino masses so small compared to those of the other quarks and leptons? The most compelling explanation is the "see-saw mechanism": Assume that left-handed neutrinos have right-handed counterparts, with mass terms of the typical size m of quark and lepton masses. However, the right-handed neutrinos have zero quantum numbers under the weak-interaction gauge group SU(2)XU(1). So no symmetry is violated if these particles get extremely large Majorana masses M. Then, diagonalizing the neutrino mass matrix gives the left-handed neutrinos masses of the size m^2/M. If m ~ 10 GeV but M ~ 10^13 GeV, we obtain neutrino masses of the order of 0.01 eV. The seesaw mechanism is usually attributed to Gell-Mann, Ramond, and Slansky (in the 1979 Sanibel and Supergravity Proceedings) and Yanagida (in the 1979 Tsukuba Proceedings; see also Prog.Theor.Phys 64,1103). But the mechanism was also "in the air" in 1979, and was rediscovered by many other authors (see for example, Glashow (Cargese, 1979)). In particular it is presented in a 1980 paper of Mohapatra and Senjanovic that appears on the topcite list at #38. Mohapatra and Senjanovic do not make it easy for their fans. Their paper is written in the context of left-right symmetric SU(2)XSU(2) weak interaction models, now badly out of fashion, and emphasizes the inverse relation between the neutrino mass and the right-handed W boson mass. However, the see-saw mechanism is clearly described. But if this paper appears on the topcite list, where are the others? To understand, please see our disclaimer below. We apologize to Gell-Mann and Ramond, to Slansky (posthumously), and to Yanagida that SPIRES does not index citations for papers published as conference proceedings in the pre-eprint era; thus their thousand citations have been lost.
In fact, none of these papers can claim true priority for the see-saw mechanism. The mechanism is stated clearly in a 1977 paper of Peter Minkowski, Phys. Lett. 67B, 421. Minkowski's paper, unjustly forgotten, had 16 citations in SPIRES as of Jan. 1, 2004. I thank Paul Frampton for bringing it to my attention.
Papers on the possible relevance of extra space dimensions for particle physics continue to hold onto high ranks in the topcites, without, however, new entries this year. In 1998, Arkani-Hamed, Dimopoulos, and Dvali suggested that the universe contains extra dimensions as large as a millimeter and that our three-dimensional world was built on a membrane (or "3-brane") in this higher-dimensional space (#8). This idea continues to attract attention and citations, 359 of the latter, at least, in the past year. The earliest papers on the phenomenological and theoretical implications of this idea, by Antoniadis, Arkani-Hamed, Dimopoulos, and Dvali, also remain topcites at #13 and #32. The paper of Horava and Witten that provided a precursor of this idea by showing that the strong coupling dynamics of the heterotic string theory could be described by matter on branes also appears on the list at #34. A lengthy review of these ideas about new space dimensions can be found in the 1999 topcites report. Subsequently, Randall and Sundrum explored the models of Nature in with branes are immersed in an extra dimension of constant curvature (#5, #9). This idea has been studied as a model-building strategy in its own right and for its deep resonance with string theory. An extensive review of the Randall-Sundrum models can be found in the 2000 topcite report.
The highest-cited papers in string theory reflect the continuing influence of Maldacena's 1997 paper that proposed a duality between conformally invariant quantum field theories in d dimensions and gravitational theories in anti-de Sitter space in (d+1) dimensions (#7). Maldacena's idea launches new approaches both to the study of gravity and to the analysis of supersymmetric gauge theories at strong coupling. After many years at the #2 position in the topcites, this work continues to receive almost 400 citations per year and has advanced to the #6 position on the all-time list. Papers by Witten and Gubser, Klebanov, and Polyakov that developed and formalized Maldacena's original idea also appear prominently, at #15 and #17, respectively, and the authoritative review of the consequences of Maldacena's duality, by Aharony, Gubser, Maldacena, Ooguri, and Oz, appears at #28. An explanation of Maldacena's duality and its consequences can be found in the 1998 topcites review.
Other string theory developments described in previous years still show their influence. The connections between string theory and noncommutative geometry, described in the 2000 topcites review, are represented by the paper of Seiberg and Witten at #16. The theory of strings on gravitation wave backgrounds, reviewed at some length in the 2002 topcite review, is represented by the paper of Berenstein, Maldacena, and Nastase that gave an amazing variety of dual representations of the physics (#18). One of the important developments in the latter subject was the identification of exact time-dependent solutions to string theory. This subject has developed extensively along other lines in the past year. In particular, Ashoke Sen (#37) has launched a study of the explicit time-dependent evolution of unstable brane configurations. Sen's solutions are interesting for the formal development of string theory, but also for the application of string ideas to brane models of inflation and other cosmological settings.
The final places on the topcites list include the description of the program PYTHIA (#36), an event generator used almost universally in experimental high energy physics for the comparison of detailed event shapes to underlying theory. The remaining places are filled by seminal theoretical papers. At #27, we find the paper of Kobayashi and Maskawa that proposed that CP violation originates in the quark mixing angles of a 6-quark Standard Model. At #41 is Hawking's original paper on radiation from black holes. At #45, we find the paper of Brodsky and Lepage on the calculation of exclusive cross sections in QCD, a paper that has become increasingly relevant for its application to B meson 2-body decays. At #48, we find the paper of Fukugita and Yanagida that proposed the right-handed neutrino Majorana mass and the CP violation in the neutrino Yukawa couplings as the esential elements in the creation of the universal matter-antimatter asymmetry. This theory has gained stature with our increased understanding of flavor-mixing in neutrino physics. Finally, at #50, we find `t Hooft's paper on the expansion of gauge theories for a large number of colors, a paper that plays a crucial role in contexts from practical perturbative QCD to Maldacena's duality and quantum gravity.
Here we present the list of all-time favorite articles in the HEP database. The list contains the 130 journal articles with more than 1,000 citations recorded since 1974 in the HEP database. Number 1 is again the `Review of Particle Properties'. The list following reads like a Who's Who of theoretical high-energy physics. 48 of the listed papers were published in Physical Review, 34 in Nuclear Physics, 21 in Physical Review Letters, 13 in Physics Letters, 7 in Communications in Mathematical Physics, 6 in Physics Reports, 3 in Journal of High Energy Physics, and 11 in other journals. Although our counting of only one year's collection of citations in the annual Top-50 list works against the inclusion of these classic papers, still 31 of these papers also appear among the 105 most highly cited articles of 2003.
The number one position in citations goes again to the Particle Data Group, accumulating over 19,000 citations to the various editions of their review. Eleven of the next fourteen papers in terms of total citations are classic theoretical papers on the structure of the Standard Model. The original papers on the unified theory of weak and electromagnetic interactions by Weinberg and Glashow appear as #2 and #7. We regret that, because Salam's original paper on this model was published in a conference proceeding, its citations are not registered in the database. The paper #3 on the list is the model of CP violation of Kobayashi and Maskawa. In the new era of B-factories, this proposal might soon be on an equally strong footing. The prototype for this model, the theory of quark mixing in weak interactions of Glashow, Iliopoulos, and Maiani, appears as #4. Another extremely influential theoretical idea that is yet to be confirmed is the concept of grand unification of elementary particle interactions. The original papers on this topic, by Georgi and Glashow and Pati and Salam appear at #12 and #15, respectively. The remaining papers in this group are the leading works on the structure of the strong interactions. Here we find the classic papers of Altarelli and Parisi on the evolution of parton distributions (#5), of Shifman, Vainshtein, and Zakharov on QCD sum rules (#8), of Wilson on the mechanism of quark confinement (#10), of Nambu and Jona-Lasinio (#13) on chiral symmetry breaking and the pion as a Goldstone boson, and of 't Hooft on the physics of instantons (#14, #18). The original papers by Politzer and Gross and Wilczek that announced the discovery of asymptotic freedom appear as #25 and #26, respectively.
Of the three top-ranked papers on subjects outside the Standard Model, two have inched their way to the top over a period of twenty years, while the third has had a meteroic rise. The papers that have climbed slowly are the now-standard reviews of supersymmetry by Nilles and by Haber and Kane; these appear at #9 and #11, respectively. As I have written in previous editions of this report, I lament the fact that these reviews are somewhat out of date; I recommend that a reader new to supersymmetry should begin with the more recent review of Martin (hep-ph/9709356). However, what I lament even more is that supersymmetry has not yet been discovered! That discovery will require all of the reviews to be rewritten.
The paper that has shot up through the topcites is of course Maldacena's paper on his famous duality. This now stands at #6, with almost 3000 citations. The papers of Witten and Gubser, Klebanov, and Polyakov that followed this work closely also now appear strikingly on the all-time list, at #21 and #33, respectively. The paper of Arkani-Hamed, Dimopoulos, and Dvali on large extra dimensions is also headed for the high reaches of the all-time list, standing this year at #24. The papers of Randall and Sundrum on physics in a curved fifth dimension are not far behind at #31 and #34.
For those who wonder where the experimental papers are, I should point out that, while seminal theoretical papers have a long life on the citation lists, experimental papers tend to make a splash which is relatively short-lived and then to have their results incorporated into the PDG compendium. To reach 1000 citations, the splash has to be gargantuan. For a long time, only one experimental discovery stirred the waters enough--the 1974 discovery of the J/psi at Brookhaven (#74) and SLAC(#90). Recently, both of these papers were overtaken by the paper from the Super-Kamiokande group announcing the discovery of atmospheric neutrino oscillations (#28).
The complete list shows titles, authors, publication information, and the exact number of citations on December 31, 2003.
Do not be disappointed if the papers that guide your work do not appear on any of the lists. The citation lists do display certain systematic biases. The most important is that experimental papers are grossly undercited, partially because experimenters surrender their citations to the PDG, and partially because theorists often look more at perceived trends than at the actual data. In addition, the citation lists, viewed on any short term, reflect the latest fashions as much as any linear progress in understanding. It is important to recall that both the unified electroweak model and superstring theory spent many years in the cellar of the citation counts before coming to prominence. Both, in their dark years, had proponents of vision who continued to study these models and eventually proved their worth to the community. Perhaps your favorite idea will also have this history, and perhaps you can even ride it to fame. In any case, we hope that you find the citation lists an instructive snapshot of the most popular trends in present day high-energy physics. An update should follow a year from now. See the page on most cited HEP articles for references to previous years.We also call your attention to a new feature of the SPIRES Web site, a list of review articles on high-energy physics, indexed by topic. We have included in this list all review articles in the SPIRES database that have at least 50 citations. We intend to update this list annually. However, many extremely useful review articles, for example, summer school lectures, receive relatively few citations. You can make this compilation more useful by recommending to us your favorite reviews (no self-citations, please). We hope that, with your advice, we can make this page a standard point of departure for anyone who wishes to learn a new speciality in high-energy physics.
The SPIRES database system at SLAC is a treasure-chest of information. The flagship database is the SPIRES-HEP literature database, a joint project of the many dedicated people from the SLAC Library, the DESY Library, and the Fermilab library. HEP contains more than half a million entries with extensive bibliographic descriptions of high-energy physics preprints, of journal articles, and of papers from the arXiv.org. The database also has pointers to viewable versions of many thousands of articles in postscript depositories worldwide. Since 1974, HEP has tracked the number of times a published high-energy physics journal article has been cited by later works. The citations are collected from the preprint version of the paper, received by the SLAC Library in advance of formal journal publication. The library receives more than 12,000 preprints yearly, and each of the preprints is a potential source of many citations.
In earlier years, the library indexed only the citations to articles published in `core' high-energy physics journals. The HEP database now also includes citations to eprints. When an eprint is published, citations from the journal version are added to the total citation count for the e-print version.
There are some important limitations to the citation count. References are taken from the preprint version of a paper. Thus articles that were never pre-printed or e-printed receive a bibliographic entry in HEP but do not have their references recorded. For further explanation, see a more detailed note on the collection of citations.
One of our goals for the future is to automatically harvest citations from the source files of eprints submitted to the Los Alamos archive. You can help us---and at the same time, make your preparation of citations easier---by copying and pasting references from SPIRES using the special LaTeX formats rather than typing in these citations yourself. Please do not omit the last, commented out, line of the format. This is the SPIRES key marking the citation for automatic retrieval.
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