Showing papers on "Parton published in 1992"
TL;DR: In this article, the authors presented a calculation of the fully exclusive parton cross sections for heavy-quark production at order O( α S 3 ) in QCD, where α is the number of quarks in the system.
590 citations
TL;DR: In this paper, the authors studied the twist-two and twist-three chiral-odd parton distributions, h 1 ( x ), h L ( x ) and e( x ), which appear in the quark density matrix of the nucleon.
353 citations
TL;DR: The parton distributions of the pion are determined from a consistent next-to-leading-order analysis of several high-statistics π ± N experiments including both Drell-Yan and prompt photon production.
Abstract: We determine the parton distributions of the pion from a consistent next-to-leading-order analysis of several high-statistics π ± N experiments including both Drell-Yan and prompt photon production
297 citations
TL;DR: In this article, a Monte Carlo event generator simulating neutral and charged current ep interactions at HERA energies and beyond is described, and the present version 4.0 of the generator optionally treats the ep scattering either by means of structure-function parametrizations or on the basis of parton distribution functions in the framework of the quark-parton model.
286 citations
TL;DR: In this article, the effect of higher-order QCD corrections on the behavior of the proton structure functions Fi(x, Q2) for fixed target and HERA energies is studied.
262 citations
TL;DR: In this article, the authors used deep inelastic scattering data to fix the parton distributions down tox ⋟10−4 and q2⋟0.3 GeV2 and showed that the predicted extrapolations are uniquely determined by the requirement of avalence-like structure of all parton distribution at some low resolution scale.
Abstract: Recent data from deep inelastic scattering experiments atx≳10−2 are used to fix the parton distributions down tox⋟10−4 andQ2⋟0.3 GeV2. The predicted extrapolations are uniquely determined by the requirement of avalence-like structure ofall parton distributions at some low resolution scale and are furthermore shown to be insensitive in the small-x region, 10−4≲x≦10−2, to the detailed experimental input at the presently accessiblex>10−2. Simple parameterizations of the resulting parton distributions are presented in the range 10−5≲x<1 and 0.3≲Q2≲108 GeV2 as obtained from the leading- and higher-order evolution equations.
241 citations
TL;DR: In this paper, a relativistic transport equation for the parton distributions is proposed for high energy nuclear colisions, which is inspired by the Parton picture of hadronic interactions.
238 citations
TL;DR: In this paper, the pionic valence distribution of the pion has been determined by using direct-γ data, and simple parametrizations of the resulting parton distributions are presented in the range 10−5≲x < 1 and 0.3≲Q2≲108 GeV2 as obtained from the leading and higher-order evolution equations.
Abstract: The gluon and sea distributions of the pion are uniquely determined by the requirement of avalence-like structure of the input parton distributions at some low resolution scale. These (dynamical) results are obtained with practically no free parameters, just using the experimentally determined pionic valence distribution combined with the constraints for the pionic gluon distribution provided by direct-γ data. Simple parametrizations of the resulting parton distributions are presented in the range 10−5≲x<1 and 0.3≲Q2≲108 GeV2 as obtained from the leading-and higher-order evolution equations.
200 citations
TL;DR: In this article, a new algorithm for finding jets ine+e− annihilation, using a jet measure based on relative transverse momentum, is presented, and compared with the standard jet-finding algorithm.
Abstract: We examine a new algorithm for finding jets ine+e− annihilation, using a jet measure based on relative transverse momentum. We perform an analytic calculation of the three-jet fraction at lowest order, and compare our result with the standard jet-finding algorithm. For soft gluons in an abelian theory it is shown that the leading double logarithms exponentiate, unlike the situation for the commonly used algorithm based on invariant mass. In QCD we find that there are leading non-abelian logarithms, and we calculate these explicitly atO(αs2). We discuss the modifications to the algorithm which are needed when the mass of a parton cluster is taken into account. The hope is that the new algorithm will allow an improved theoretical analysis at smaller values of the resolution parameteryT, and hence an improved fit to the experimental data.
103 citations
TL;DR: In this paper, the Drell-Yan process is used to measure the transverse spin polarization distribution of quarks in a proton, which contributes at leading twist to the angular distribution of lepton pair production in doubly polarized proton-proton collisions.
Abstract: The transverse spin polarization distribution of quarks in a proton contributes at leading twist to the angular distribution of lepton pair production in doubly polarized proton-proton collisions. Although this distribution is straightforward to define in the QCD-improved parton model and represents a fundamental quark degree of freedom, it has never been measured. Moreover, deeply inelastic electroproduction experiments are only sensitive to this distribution at the higher twist level, and then mix this contribution with others, including the one coming from multiparton initial states. Reviewing this, we conclude that the Drell-Yan process is the best way to measure the quark transverse spin polarization distribution.
99 citations
TL;DR: In this paper, the authors investigated the all-order resummation of soft collinear gluon emission from initial quarks and gluons participating in heavy quark inclusive production.
CERN1
TL;DR: In this paper, a new concept, the handedness of a jet, which can be used to determine the polarization of a high-energy quark or gluon produced in a hard collision was introduced.
TL;DR: In this article, a study of jet production in p p interactions with √s=630 GeV at the CERN S p p S- Collider, which are tagged by a proton or antiproton which possesses more than 90% of the incident beam momentum.
TL;DR: In this article, it was shown that the high energy limit of quark-quark, or gluon-gluon, elastic scattering is calculable in terms of the BFKL pomeron when − t / Λ 2 ⪢ 1.
TL;DR: In this paper, the angular decay distribution of leptons from W-production at high-qT in p p collisions was measured and it was shown that large deviations from the well-known (1+cos θ2) distribution valid at low-qTs are expected already at moderate transverse W-momentum (qT≈20GeV).
TL;DR: In this paper, shadowing in lepton-deuteron scattering is analyzed using double interaction formalism where they relate shadowing to inclusive diffractive processes and find that the shadowing effects are very small, less than 2% or so.
TL;DR: In this article, the structure of hadronic events from Z ≥ 0 decay is studied by measuring event shape variables, factorial moments, and the energy flow distribution, after correction for detector effects and initial and final state radiation, compared with the predictions of different QCD Monte Carlo programs with optimized parameter values.
Abstract: The structure of hadronic events fromZ
0 decay is studied by measuring event shape variables, factorial moments, and the energy flow distribution. The distributions, after correction for detector effects and initial and final state radiation, are compared with the predictions of different QCD Monte Carlo programs with optimized parameter values. These Monte Carlo programs use either the second order matrix element or the parton shower evolution for the perturbative QCD calculations and use the string, the cluster, or the independent fragmentation model for hadronization. Both parton shower andO(α
2
s
matrix element based models with string fragmentation describe the data well. The predictions of the model based on parton shower and cluster fragmentation are also in good agreement with the data. The model with independent fragmentation gives a poor description of the energy flow distribution. The predicted energy evolutions for the mean values of thrust, sphericity, aplanarity, and charge multiplicity are compared with the data measured at different center-of-mass energies. The parton shower based models with string or cluster fragmentation are found to describe the energy dependences well while the model based on theO(α
2
s
calculation fails to reproduce the energy dependences of these mean values.
TL;DR: The dual parton model, formulated as a Monte Carlo event generator, describes soft and semihard multiparticle production and finds a reasonable agreement with experimental data on the energy range of the hadron colliders, rapidity distributions and the rise of the rapidity plateau with the collision energy, transverse-momentum distributions andthe rise of average transverse momenta.
Abstract: The dual parton model (DPM) describes soft and semihard multiparticle production. The version of the DPM presented in this paper includes soft and hard mechanisms as well as diffractive processes. The model is formulated as a Monte Carlo event generator. We calculate in this model, in the energy range of the hadron colliders, rapidity distributions and the rise of the rapidity plateau with the collision energy, transverse-momentum distributions and the rise of average transverse momenta with the collision energy, multiplicity distributions in different pseudorapidity regions, and transverse-energy distributions. For most of these quantities we find a reasonable agreement with experimental data.
TL;DR: A relativistic kinetic formulation of the time evolution of parton distributions during the early pre- equilibrium stage of nucleus-nucleus collisions at the BNL Relativistic Heavy Ion Collider and CERN Large Hadron Collider is presented to study the microscopic dynamics and equilibration of the system.
Abstract: A relativistic kinetic formulation of the time evolution of parton distributions during the early pre- equilibrium stage of nucleus-nucleus collisions at the BNL Relativistic Heavy Ion Collider (RHIC) and CERN Large Hadron Collider (LHC) is presented to study the microscopic dynamics and equilibration of the system. The nuclear collision is described as a sequence of multiple hard and soft parton-parton collisions and associated parton emission and absorption processes. Important aspects for the space-time evolution of the partonic system are the balance between emissive and absorptive processes, dilated formation of gluon radiation, and the effects of soft gluon interference. The time evolution of central [sup 32]S+[sup 32]S and [sup 197]Au+[sup 197]Au collisions at RHIC ([radical][ital s] =200[ital A] GeV) is studied in complete phase space and the approach to equilibrium is investigated. The results obtained imply the formation of hot quark-gluon plasmas in these collisions with estimated equilibriation times, temperatures, and energy densities of [tau][sub eq][congruent]1.2 (1.8) fm/[ital c], [ital T][congruent]290 (325) MeV, and [epsilon][congruent]17 (31) GeV/fm[sup 3] for [sup 32]S+[sup 32]S ([sup 197]Au+[sup 197]Au). The consequences of such rather high temperatures and energy densities should be clear quark-gluon plasma signatures, observable in the production of charm, strangeness, direct photons, andmore » dileptons.« less
TL;DR: The enhancement of the final total open charm in the central region due to preequilibrium production could be used as a measure of the thermalization time of the dense partonic system.
Abstract: Preequilibrium parton scattering is shown to make an important contribution to the charm production in relativistic heavy ion collisions. In contrast to the gluon shadowing effect in the initial parton scattering, the enhancement of the final total open charm in the central region due to preequilibrium production could be used as a measure of the thermalization time of the dense partonic system.
TL;DR: In this article, the authors discuss the measurement of regions in the proton where the density of small-x partons is large, called hot spots, by means of an associated jet analysis.
Abstract: In this paper we discuss the measurement of regions in the proton where the density of small-x partons is large, called “hot spots”, by means of an associated jet analysis. An analytical estimate of the cross section is presented and the jet kinematics is discussed in the HERA and LEP-LHC frame. A Monte Carlo estimate shows that the number of jets produced in deep inelastic scattering events at HERA, suitable for this analysis, amounts to a few 1000 jcts for a data sample with an integrated luminosity of about 10 pb−1.
TL;DR: Spectator model decay rates are predicted for inclusive semileptonic decays of the Λb baryon and the B meson, in the limit of a very heavy b quark, in lowest order of perturbative QCD.
TL;DR: In this paper, an energy distribution function for the incoming hadron without involving parton decay functions for the outgoing partons is defined, which can be computed in terms of parton distribution functions.
TL;DR: In this article, it was shown that the heavy-quark fraction is suprisingly large and remarkably insensitive to changes in the mass factorization scale and/or the choice of parton densities.
TL;DR: In this article, the energy spectra of partons from QCD cascades truncated at different values of the cutoff parameter Q0 are used to model the energy distributions of massive hadrons in the framework of the local parton-hadron duality hypothesis.
Abstract: New results in applications of the analytical perturbative approach to the description of particle distributions in QCD jets are presented We study inclusive energy spectra of partons from QCD cascades truncated at different values of the cutoff parameter Q0, which can be used to model the energy distributions of massive hadrons in the framework of the local parton-hadron duality hypothesis Results of straightforward numerical calculations of parton distributions which solve the MLLA evolution equations are compared to approximate formulas representing the spectra in terms of a few analytically calculated shape parameters
CERN1
TL;DR: In this paper, a modification of the structure functions in nuclei leads to reduced production relative to pp interactions, and parton scattering in nuclear matter broadens the transverse momentum spectrum.
TL;DR: In this paper, it was shown that the proof of the theorem determines the operator form for the parton densities for hard processes in QCD with transversely polarized incoming hadrons.
Abstract: I show that factorization for hard processes in QCD is also valid when the detected particles are polarized, and that the proof of the theorem determines the operator form for the parton densities. Particular attention is given to the case of transversely polarized incoming hadrons.
TL;DR: In this article, the authors presented the first next-to-leading order calculation of the single jet inclusive cross section at the ep collider HERA and verified that their results are much less sensitive to the choice of renormalization/factorisation scales than the leading order results.
TL;DR: In this paper, the authors derived a scheme to solve the integral equations for inclusive multiparton densities in the double logarithmic approximation of QCD and presented the explicit solution for the angle dependent two parton correlation function, in the case of constant α s.