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Showing papers on "Parton published in 1993"


Journal ArticleDOI
TL;DR: In this paper, it was shown that the azimuthal dependence of the distribution of hadrons in a quark jet is a probe of the transverse spin of the quark initiating the jet.

695 citations


Journal ArticleDOI
TL;DR: In this article, a general method for calculating the fully differential cross section for the production of jets at next-to-leading order in a hadron collider is described. But this method is based on a "crossing" of calculations with all partons in the final state.

394 citations


Journal ArticleDOI
TL;DR: In hadron-hadron collisions, production of Higgs bosons and other color-singlet systems can occur via fusion of electroweak bosons, occasionally leaving a ``rapidity gap'' in the underlying-event structure, which is studied to see whether it serves as a signature for detection of the Higgs Bosons, etc.
Abstract: In hadron-hadron collisions, production of Higgs bosons and other color-singlet systems can occur via fusion of electroweak bosons, occasionally leaving a ``rapidity gap'' in the underlying-event structure. This observation, due to Dokshitzer, Khoze, and Troyan, is studied to see whether it serves as a signature for detection of the Higgs bosons, etc. We find it is a very strong signature at subprocess c.m. energies in excess of a few TeV. The most serious problem with this strategy is the estimation of the fraction of events containing the rapidity gap; most of the time the gap is filled by soft interactions of spectator degrees of freedom. We also study this question and estimate this ``survival probability of the rapidity gap'' to be of order 5%, with an uncertainty of a factor 3. Ways of testing this estimate and further discussion of the underlying hard-diffraction physics are presented.

275 citations


Journal ArticleDOI
TL;DR: In this paper, a general method for calculating the fully differential cross section for the production of jets at next-to-leading order in a hadron collider is described, which is based on a ''crossing'' of first-order calculations with all partons in the final state.
Abstract: We describe a general method of calculating the fully differential cross section for the production of jets at next-to-leading order in a hadron collider. This method is based on a `crossing' of next-to-leading order calculations with all partons in the final state. The method introduces universal crossing functions that allow a modular approach to next-to-leading order calculations for any process with initial state partons. These techniques are applied to the production of jets in association with a vector boson including all decay correlations of the final state observables.

261 citations


Journal ArticleDOI
TL;DR: In this article, the authors refine their recent determination of parton distributions with the inclusion of the new published sets of precise muon and neutrino deep inelastic data.

258 citations


Journal ArticleDOI
TL;DR: In this paper, the conditions of instability of the parton momentum distribution are found and the characteristic time of its development is estimated, and the relevance of the phenomenon for heavy-ion collisions at RHIC and LHC is briefly discussed.

220 citations


Journal ArticleDOI
TL;DR: The fragmentation functions for a gluon to split into [ital S]-wave quarkonium states to leading order in the QCD coupling constant are calculated using perturbative QCD.
Abstract: The dominant production mechanism for heavy-quark--antiquark bound states with large transverse momentum is fragmentation, the splitting of a high energy parton into a quarkonium state and other partons. We show that the fragmentation functions D(z,\ensuremath{\mu}) describing these processes can be calculated using perturbative QCD. We calculate the fragmentation functions for a gluon to split into S-wave quarkonium states to leading order in the QCD coupling constant.

195 citations


Journal ArticleDOI
TL;DR: A set of rate equations describing the chemical equilibration of gluons and quarks including medium effects on the relevant QCD transport coefficients are derived, and their consequences for parton equilibrations in heavy ion collisions are discussed.
Abstract: We investigate the processes leading to phase-space equilibration of parton distributions in nuclear interactions at collider energies. We derive a set of rate equations describing the chemical equilibration of gluons and quarks including medium effects on the relevant QCD transport coefficients, and discuss their consequences for parton equilibration in heavy ion collisions.

183 citations


Journal ArticleDOI
TL;DR: The authors describes salient features of new sets of parton distributions obtained by the CTEQ Collaboration based on a comprehensive QCD global analysis of all available data The accuracy of the new data on deep inelastic scattering structure functions obtained by very high statistics NMC and CCFR experiments provides unprecedented sensitivity to the flavor dependence of the sea-quark distributions.

180 citations


Journal ArticleDOI
Hartmute Plothow-Besch1
TL;DR: PDFLIB as discussed by the authors is an integrated package of parton density functions, which has been added to the CERN Program Library Pool W999 and is labelled as W5051, and offers a program to calculate the strong coupling constant αS to first or second order (default).

143 citations


Journal ArticleDOI
S. Frixione1
TL;DR: In this paper, the production of W+W− pairs at hadron colliders with a full O(αs) differential calculation was discussed and the complete analytical result for the partonic cross section was given.

Journal ArticleDOI
TL;DR: A discrete spectrum of bound states is found, with the logarithm of the level density growing approximately linearly with the mass, in the large-[ital N] limit of (1+1)-dimensional QCD coupled to Majorana fermions.
Abstract: We consider (1+1)-dimensional QCD coupled to Majorana fermions in the adjoint representation of the gauge group SU([ital N]). Pair creation of partons (fermion quanta) is not suppressed in the large-[ital N] limit, where the glueball-like bound states become free. In this limit the spectrum is given by a linear light-cone Schroedinger equation, which we study numerically using the discretized light-cone quantization. We find a discrete spectrum of bound states, with the logarithm of the level density growing approximately linearly with the mass. The wave function of a typical excited state is a complicated mixture of components with different parton numbers. A few low-lying states, however, are surprisingly close to being eigenstates of the parton number, and their masses can be accurately calculated by truncated diagonalizations.

Journal ArticleDOI
TL;DR: In this article, a FRITIOF implementation of the Rutherford Parton scattering (RPS) is presented, which predicts a restoration of KNO scaling as a good approximation in the TeV energy regime.
Abstract: We implement the high-P T dynamics, namely parton scattering of the Rutherford type, into the framework of the FRITIOF model. Such high-P T effects are increasingly important in hadronic collisions at higher energies and it is crucial to include them for a model intended to describe the collision and particle production processes. In our treatment the Rutherford parton scattering (RPS) is intimately related to the gluon bremsstrahlung radiation. By investigating their interrelation we arrive at a FRITIOF implementation of RPS which is infrared stable. The results of the model are in excellent agreement with experimental data up to the highest energies. The model predicts a restoration of KNO scaling as a good approximation in the TeV energy regime.

Journal ArticleDOI
TL;DR: In this paper, it was pointed out that the predictions of radiatively (dynamically) generated parton distributions are in satisfactory agreement with recent small-x measurements and moderate modifications of the valence-like input (mainly u ) remove possibly small discrepancies between experiment and theoretical predictions at x>10−2, but do not significantly affect the (steep) radiative predictions for x ≥ 10−2.

Journal ArticleDOI
TL;DR: In this article, the small-x behaviour of the parton anomalous dimensions in perturbative QCD beyond the leading logarithmic approximation was discussed, and the flavour non-singlet anomalous dimension was found to be regular at small x.

Journal ArticleDOI
TL;DR: In this paper, the influence of string fusion on the basic features of relativistic heavy-ion collisions is studied with the help of a Monte Carlo string fusion model based on the parton picture of strong interactions and includes the string fusion phenomenon.

Journal ArticleDOI
TL;DR: In this article, the authors studied the photonic production via deep inelastic quark and gluon fragmentation in the framework of a specific factorization scheme chosen to provide the maximally possible amount of perturbative stability.
Abstract: Photon production via deep inelastic quark and gluon fragmentation is studied beyond the leading perturbative order within the framework of a specific factorization scheme ($\mathrm{DI}{\mathrm{S}}_{\ensuremath{\gamma}}$) chosen to provide the maximally possible amount of perturbative stability. It is argued that the perturbative (pointlike) results are expected to present a realistic estimate for photonic fragmentation functions, and the ambiguities related to the presently unknown, but possibly small, nonperturbative hadronic contributions are pointed out.

Journal ArticleDOI
TL;DR: In this article, the authors derived a quantum mechanical upper bound on the amount of radiative energy loss suffered by high energy quarks and gluons in nuclear matter and showed that the nuclear suppression observed in quarkonium production at high xF cannot be explained in terms of energy loss of the initial or final parton states.

Journal ArticleDOI
TL;DR: In this paper, the authors clarified conflicting results in the literature on coefficient functions in front of higher twist operators contributing to the parton sum rules for deep inelastic scattering from polarized targets.
Abstract: We clarify conflicting results in the literature on coefficient functions in front of higher twist operators contributing to the parton sum rules for deep inelastic scattering from polarized targets. The necessary corrections do not affect our calculations of matrix elements, published in Phys.Lett.B242(1990)245, but change final estimates of the $\sim 1/Q^2$ contributions to Bjorken and Ellis--Jaffe sum rules.

Journal ArticleDOI
TL;DR: Perturbative analysis of parton kinetics for high energy nuclear collisions shows that thermal equilibration of gluons happens very fast, while quark production is much slower, and a simple minimal model is proposed which includes only incoming quarks and antiquarks.
Abstract: Perturbative analysis of parton kinetics for high energy nuclear collisions shows that thermal equilibration of gluons happens very fast, while quark production is much slower. A simple ``minimal model'' is proposed which includes only incoming quarks and antiquarks. We have found that a smaller quark number is more than compensated by the fact, that they are imbedded into the hotter glue. Predicted yield of dileptons and photons in the interesting kinematic region are larger than considered before, and are quite observable at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider.


Journal ArticleDOI
TL;DR: In this article, the production of gauge bosons such as W ± and Z in pp collisions up to √ s = 0.5 TeV was examined in connection with the realistic possibility of having polarized proton beams at RHIC with a high luminosity.

Journal ArticleDOI
TL;DR: The chemical composition of the hot and dense parton matter formed in the central region of ultrarelativistic heavy-ion collisions is studied for the case of Au+Au collisions at energies reached at the BNL RHIC using the parton cascade model and a chemical equilibration between the gluons and the quarks cannot be achieved.
Abstract: The chemical composition of the hot and dense parton matter formed in the central region of ultrarelativistic heavy-ion collisions is studied for the case of Au+Au collisions at energies reached at the BNL RHIC using the parton cascade model. It is shown that within this framework, which is based on current understanding of semihard and hard interactions in QCD including the emission and absorption of soft partons, a chemical equilibration between the gluons and the quarks cannot be achieved. The gluons and $u$, $d$, $s$, and $c$ quarks all rapidly approach kinetic equilibrium with a common temperature. The gluons subsequently also achieve chemical equilibrium, but the light quarks only reach about 60% of their ideal chemical equilibrium densities. It is demonstrated that the baryon density in the central region is small relative to the total parton density, with an associated ratio of baryon chemical potential to temperature of 0.35, slowly decreasing with time. The implications of the formation of such a hot, gluon-dominated plasma for strangeness, charm, and dilepton production are discussed.

Journal ArticleDOI
TL;DR: In this paper, the evolution of the parton distribution in nuclei is studied by using distributions at an initial scale Q 0 = 2 GeV which conserve baryon charge and momentum.

Journal ArticleDOI
TL;DR: A phenomenological cluster hadronization scheme for partons in nuclear collisions is presented and combined with the earlier developed parton cascade model to provide a comprehensive description of highly relativistic hadron-hadron and nucleus-nucleus collisions.
Abstract: A phenomenological cluster hadronization scheme for partons in nuclear collisions is presented and combined with the earlier developed parton cascade model to provide a comprehensive description of highly relativistic hadron-hadron and nucleus-nucleus collisions. The model as a whole allows one to study the time evolution of the collisions in complete phase space from the instant of nuclear contact, via the perturbative QCD evolution of parton distributions, to the formation of final hadronic states. The application of this approach to [ital p[bar p]] collisions at [radical][ital s] =200--1800 GeV yields a decent agreement with the experimentally measured momentum and multiplicity distributions. Heavy ion collisions are illustratively studied in the case of central Au+Au collisions at the BNL energies of Relativistic Heavy Ion Collider (RHIC) ([radical][ital s] =200[ital A] GeV) and the CERN Large Hadron Collider (LHC) ([radical][ital s] =6300[ital A] GeV). The impact of a number of nuclear and medium effects on the inclusive hadron production is analyzed and predictions for charged particle spectra and multiplicities are given. In particular, the model results for the central rapidity densities of charged particles are [congruent]1200 ([radical][ital s] =200[ital A] GeV) and [congruent]2500 ([radical][ital s] =6300[ital A] GeV), which is a factor of [similarmore » to]2.5 per nucleon larger than in [ital p]+[ital p] collisions at corresponding energies.« less

Journal ArticleDOI
TL;DR: In this article, a QCD-inspired model of nucleons, treated, in the limit of vanishingQ2, as bound states of three relativistic constituent quarks, is presented.
Abstract: We describe the nuclear structure functions in the whole range of the Bjorken variablex, by combining various effects in a many-step procedure. First, we present a QCD motivated model of nucleons, treated, in the limit of vanishingQ2, as bound states of three relativistic constituent quarks. Gluons and sea quarks are generated radiatively from the input valence quarks. All parton distributions are described in terms of the confinement (or nucleon's) radius. The results for free nucleons are in agreement with the experimental determinations. The structure functions of bound nucleons are calculated by assuming that the main effect of nucleon binding is stretching of nucleons. The larger size of bound nucleons lowers the valence momentum and enhances the radiatively generated glue and sea densities. In the small-x region the competitive mechanism of nuclear shadowing takes place. It also depends on the size of the nucleons. By combining stretching, shadowing and Fermi motion effects (the latter confined to very largex), the structure function ratio is well reproduced. Results are also presented for theA-dependence of the momentum integral of charged partons, the nuclear gluon distribution and the hadron-nuclei cross sections.

Journal ArticleDOI
TL;DR: In this paper, the authors defined 14 nucleon structure functions in the standard model and analyzed their Bjorken scaling and Regge behavior in deeply inelastic lepton-nucleon scattering in perturbative QCD.

Journal ArticleDOI
TL;DR: Perturbative QCD corrections to the branching ratio of ηt into γγ are included and the two-loop QCD potential is used to predict the wave function at the origin.
Abstract: Toponium production at future hadron colliders is investigated. Perturbative QCD corrections to the production cross section for gluon fusion are calculated as well as the contributions from gluon-quark and quark-antiquark collisions to the total cross section. The dependence on the renormalization and factorization scales and on the choice of the parton distribution functions is explored. QCD corrections to the branching ratio of ηt into γγ are included and the two-loop QCD potential is used to predict the wave function at the origin. The branching ratio of ηt into γZ, ZZ, HZ and W W is compared with the γγ channel.

Journal ArticleDOI
TL;DR: In this article, it was shown that the proof of the theorem determines the operator form the parton densities for hard processes in QCD with transversely polarized incoming hadrons.

Journal ArticleDOI
TL;DR: In this article, a model using a pomeron structure function dominated by either quarks or gluons was proposed to calculate diffractive W/Z production and find observably large cross-sections at the Tevatron energy.