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Showing papers on "Parton published in 1994"


Journal ArticleDOI
TL;DR: It is shown that the gluon distribution function for very large nuclei may be computed for small transverse momentum as correlation functions of an ultraviolet finite two-dimensional Euclidean field theory.
Abstract: We show that the gluon distribution function for very large nuclei may be computed for small transverse momentum as correlation functions of an ultraviolet finite two-dimensional Euclidean field theory. This computation is valid to all orders in the density of partons per unit area, but to lowest order in ${\ensuremath{\alpha}}_{s}$. The gluon distribution function is proportional to $\frac{1}{x}$, and the effect of the finite density of partons is to modify the dependence on the transverse momentum for small transverse momenta.

1,206 citations


Journal ArticleDOI
TL;DR: Based on QCD-inspired models for multiple jets production, the authors developed a Monte Carlo program to study jet and the associated particle production in high energy pp, pA and AA collisions.

722 citations


Journal ArticleDOI
TL;DR: In this paper, the authors derived the non-abelian analog of the Landau-Pomeranchuk effect that suppresses induced soft radiation with formation times exceeding the mean free path.

596 citations


Journal ArticleDOI
TL;DR: The dual parton model (DPM) as mentioned in this paper provides a complete, phenomenological description of all facets of soft processes and has been extensively studied and gradually extended over the past twelve years.

520 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that large formation times of bremsstrahlung quanta determine the QCD radiation intensity and derive the gluon energy spectrum, and that the energy loss of fast partons in a QCD medium depends on the incident energy.
Abstract: Soft gluon radiation induced by multiple scattering of a fast quark or gluon propagating through QCD matter is discussed. After revisiting the Landau-Pomeranchuk-Migdal effect in QED we show that large formation times of bremsstrahlung quanta determine the QCD radiation intensity (in analogy to QED) and derive the gluon energy spectrum. Coherent suppression takes place as compared to the Bethe-Heitler situation of independent emissions. As a result the energy loss of fast partons in a QCD medium depends on the incident energy $E$ similarly to QED, $-dE/dz \propto \sqrt{E}$.

242 citations


Journal ArticleDOI
T. Ahmed1, S. Aid2, Vladimir Andreev, B. Andrieu3  +391 moreInstitutions (27)
TL;DR: In this paper, the H1 detector at HERA was used for a class of deep inelastic electron-proton scattering (DIS) events (5 < Q2 < 120 GeV2) at low Bjorken-x (10−4 < x < 10−2) which have almost no hadronic energy flow in a large interval of pseudo-rapidity around the proton remnant direction and which cannot be attributed to our present understanding of DIS and fluctuations in final state hadronic fragmentation.

139 citations


Journal ArticleDOI
TL;DR: In this article, the authors provided thermodynamic quantities of pure SU(3) gauge theory in lattice approximation, which are thermodynamically selfconsistent, i.e., energy density and pressure are related via e = T∂p/∂T - p, and exhibit a striking difference from the popular bag model parametrization p = e/3 - 4B/3.

130 citations


Journal ArticleDOI
TL;DR: The perturbative stability of heavy quark pair production at high energy ep and pp colliders is studied and demonstrated within the context of the pair production fusion mechanisms relevant for F2,Lh(x, Q2) and hadronic total heavy flavor production cross sections as discussed by the authors.

128 citations


Journal ArticleDOI
TL;DR: In this article, the singular terms of the helicity amplitudes of n-parton processes at one loop were obtained by using color algebra and tree-level tree level and simple color algebra.

124 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of order α s and order s 2 corrections to the deep inelastic coefficient functions (singlet and non-singlet) contributing to the polarized structure function g 1 ( x, Q 2 ) was studied.

111 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the parton distributions at small x using moments of the Gribov-Lipatov-Altarelli-Parisi (GLAP) evolution equation with respect to x.

Journal ArticleDOI
TL;DR: In this article, a next-to-leading-order calculation of the fully exclusive parton cross section at the photoproduction of heavy quarks is presented, and the authors use their result to compute quantities of interest for current fixed-target experiments.

Journal ArticleDOI
W. J. Stirling1
TL;DR: In this paper, the authors studied the BFKL "perturbative pomeron" equation of Quantum Chromodynamics for the production of jet pairs with small transverse momentum and large relative rapidity in high energy hadron-hadron collisions.

Journal ArticleDOI
Thomas Mannel1
TL;DR: In this article, the first nonvanishing corrections to the parton model result are given and the lepton energy spectrum of inclusive semileptonic decays of heavy mesons is calculated.

Journal ArticleDOI
TL;DR: In this paper, the photon structure function beyond the leading logarithm approximation is discussed in detail, and the effect of the charm quark mass threshold on the phenomenology is discussed.
Abstract: We discuss in detail the photon structure function beyond the leading logarithm approximation. Of special concern is the factorization scheme and the hadronic input; we show how to naturally absorb large terms due to the\(\overline {MS} \) factorization scheme in a modified hadronic component. The effect of the charm quark mass threshold is also discussed in relation to the phenomenology. A comparison with data shows that the modified hadronic component can be reasonably described by a VDM-type input.

Journal ArticleDOI
TL;DR: In this paper, the effect of the charm quark mass threshold on the photon structure function was discussed in relation to the phenomenology, and a comparison with data showed that the modified hadronic component can be reasonably described by a VDM-type input.
Abstract: We discuss in detail the photon structure function beyond the leading logarithm approximation. Of special concern is the factorization scheme and the hadronic input; we show how to naturally absorb large terms due to the MSbar factorization scheme in a modified hadronic component. The effect of the charm quark mass threshold is also discussed in relation to the phenomenology. A comparison with data shows that the modified hadronic component can be reasonably described by a VDM-type input.

Journal ArticleDOI
TL;DR: The screening of the static chromoelectric field in the nonequilibrium plasma is studied and importance of the two phenomena for heavy-ion collisions at the Brookhaven Relativistic Heavy Ion Collider and the CERN Large Hadron Collider is critically discussed.
Abstract: Hard and semihard processes lead to a copious production of partons at the early stage of ultrarelativistic heavy-ion collisions. Since the parton momentum distribution is strongly anisotropic, the system can be unstable with respect to the specific plasma modes. The conditions of instability are found and the characteristic time of its development is estimated. Then, the screening of the static chromoelectric field in the nonequilibrium plasma is studied. Importance of the two phenomena for heavy-ion collisions at the Brookhaven Relativistic Heavy Ion Collider and the CERN Large Hadron Collider is critically discussed.

Journal ArticleDOI
TL;DR: Details of the use of factorization at higher twist to describe multiple scattering in nuclei are presented, and the methods described here are applicable to a variety of other high-[ital p][sub [ital T]] cross sections.
Abstract: We derive the anomalous nuclear dependence of jet cross sections in deeply inelastic scattering and photoproduction, in terms of twist-four parton distributions in nuclei. This paper presents details of the use of factorization at higher twist to describe multiple scattering in nuclei, and the methods described here are applicable to a variety of other high-${\mathit{p}}_{\mathit{T}}$ cross sections.

Journal ArticleDOI
Dirk Graudenz1
TL;DR: In this article, a finite one-particle inclusive cross section in deeply inelastic lepton-nucleon scattering, expressed in terms of parton densities and fragmentation functions being differential in the invariant mass of the observed hadron and of the incoming nucleon, was derived.

Journal ArticleDOI
TL;DR: In this paper, anomalous nuclear enhancement in the photoproduction of jets as a higher-twist process in perturbative QCD was analyzed and a physical interpretation of the nuclear enhancement as a measure of the average net transverse color force on an off-shell parton moving through nuclear matter was given.
Abstract: We analyze anomalous nuclear enhancement in the photoproduction of jets as a higher-twist process in perturbative QCD. We use the Fermilab E683 data on dijet momentum imbalance to estimate the size of the relevant twist-4 parton distributions. We find that twist-4 matrix elements are of the order of 0.05-0.1 ${\mathrm{GeV}}^{2}$ times typical twist-2 parton distributions. We discuss a physical interpretation of the nuclear enhancement as a measure of the average net transverse color force on an off-shell parton moving through nuclear matter, and give an order-of-magnitude estimate for the typical squared transverse field strengths encountered by a fast moving parton.

Journal ArticleDOI
TL;DR: The ratio of cumulant to factorial moments reveals an oscillatory structure which is very sensitive to tiny details of the distributions in quark and gluon jets.
Abstract: Parton correlations in quark and gluon jets are studied by calculating moments of their multiplicity distributions in fixed-coupling QCD. An exact solution of the problem for moments of any rank is found. The ratio of cumulant to factorial moments reveals an oscillatory structure which is very sensitive to tiny details of the distributions.

Journal ArticleDOI
TL;DR: A number of quark fragmentation functions for spin-0, -1/2, and -1 hadrons are defined and classified according to their twist, spin, and chirality, and used to analyze semi-inclusive deep-inelastic scattering on a transversely polarized nucleon.
Abstract: We define a number of quark fragmentation functions for spin-0, -\textonehalf{}, and -1 hadrons, and classify them according to their twist, spin, and chirality. As an example of their applications, we use them to analyze semi-inclusive deep-inelastic scattering on a transversely polarized nucleon.

Journal ArticleDOI
TL;DR: In this article, the authors calculate the valence distribution of down quarks and up quarks in the proton and the neutron, taking into account the major sources of charge symmetry violation, including the effect of the mass difference of u and d quarks on the bag wave function, and the masses of the intermediate diquark states.
Abstract: We calculate the valence distribution of down quarks in the proton and up quarks in the neutron (the ‘minority’ quark distributions), taking into consideration the major sources of charge symmetry violation, including the effect of the mass difference of the u and d quarks on the bag wave function, and the masses of the intermediate diquark states. The relative difference of the distributions can be as large as 10% for intermediate values of Bjorken x.

Journal ArticleDOI
TL;DR: Although the parton content of the electron in general no longer factorizes into an electron flux function and a photon structure function, it can still be expressed as a single integral.
Abstract: We point out that in processes involving the parton content of the photon the usual effective photon approximation should be modified. The reason is that the parton content of virtual photons is logarithmically suppressed compared to real photons. We describe this suppression using several simple, physically motivated [ital Ansa]$[ital uml---tze]. Although the parton content of the electron in general no longer factorizes into an electron flux function and a photon structure function, it can still be expressed as a single integral. Numerical examples are given for the [ital e][sup +][ital e][sup [minus]] collider TRISTAN as well as the [ital ep] collider HERA.

Journal ArticleDOI
TL;DR: In this article, the production of W± and Z gauge bosons in proton-proton and protonneutron collisions up to a center-of-mass energy √s = 0.5 TeV was studied.

Journal ArticleDOI
M. Acciarri, A. Adam, O. Adriani1, M. Aguilar-Benitez2  +500 moreInstitutions (21)
TL;DR: In this paper, the authors present a study of the inclusive production of π0, η, Ks0 and Λ based on 929,000 hadronic Z decays recorded with the L3 detector at LEP.

Journal ArticleDOI
TL;DR: In this article, a semi-analytical approach to the model independent leptonic QED corrections to deep inelastic neutral current lepton-nucleon scattering is presented.
Abstract: We give an exhaustive presentation of the semi-analytical approach to the model independent leptonic QED corrections to deep inelastic neutral current lepton-nucleon scattering. These corrections include photonic bremsstrahlung from and vertex corrections to the lepton current of the order ${\cal O}(\alpha)$ with soft photon exponentiation. % A common treatment of these radiative corrections in several variables -- leptonic, hadronic, mixed, Jaquet-Blondel variables -- has been developed and double differential cross-sections are calculated. In all sets of variables we use some structure functions, which depend on the hadronic variables and which do not have to be defined in the quark parton model. The remaining numerical integrations are twofold (for leptonic variables) or onefold (for all other variables). For the case of hadronic variables, all phase space integrals have been performed analytically. Numerical results are presented for a large kinematical range, covering fixed target as well as collider experiments at HERA or LEP$\otimes$LHC, with a special emphasis on HERA physics.

01 Jan 1994
TL;DR: In this article, the production of W ± and Z gauge bosons in protonproton and proton-neutron collisions up to a center-of-mass energy √ s = 0.5 TeV, in connection with the realistic possibility of having proton deuteron collisions at RHIC with a high luminosity.
Abstract: We study the production of W ± and Z gauge bosons in proton-proton and proton-neutron collisions up to a center-of-mass energy √ s = 0.5 TeV , in connection with the realistic possibility of having proton-deuteron collisions at RHIC with a high luminosity. We stress the importance of measuring unpolarized cross sections for a better determination of the flavor asymmetry of the sea quarks. Since polarized proton beams will be available at RHIC, we evaluate several spin-dependent observables like, double helicity asymmetries ALL as a test of the sea quark polarization, double transverse spin asymmetries AT T as a practical way to determine a new structure function, the nucleon transversity distribution h1(x), and parity-violating asymmetries AL as a further test of our present knowledge of polarized parton distributions.

Journal ArticleDOI
TL;DR: In this article, the transport interaction rates of elastic scattering processes of thermal partons in the quark-gluon plasma were calculated beyond the leading logarithm approximation using the effective perturbation theory for QCD at finite temperatures developed by Braaten and Pisarski.
Abstract: The transport interaction rates of elastic scattering processes of thermal partons in the quark-gluon plasma are calculated beyond the leading logarithm approximation using the effective perturbation theory for QCD at finite temperatures developed by Braaten and Pisarski. The results for the ordinary and transport interaction rates obtained from the effective perturbation theory are compared to perturbative approximation based on an infrared cutoff by the Debye screening mass. The relevance of those interaction rates for quark-gluon plasma possibly formed in ultrarelativistic heavy ion collision is discussed.

Journal ArticleDOI
TL;DR: In this paper, a systematic study of the inclusive single heavy quark and heavy-quark pair production cross sections in pp collisions is presented for RHIC and LHC energies, and the dependence of the rates on the renormalization and factorization scales is discussed.
Abstract: A systematic study of the inclusive single heavy quark and heavy-quark pair production cross sections in pp collisions is presented for RHIC and LHC energies. We compare with existing data when possible. The dependence of the rates on the renormalization and factorization scales is discussed. Predictions of the cross sections are given for two different sets of parton distribution functions.