Showing papers on "Parton published in 1990"
TL;DR: In this article, a Born and one-loop approximation was used to extract quark and gluon distributions from a source consisting of a nucleus of heavy quarkonium bound states, states well understood in QCD.
445 citations
TL;DR: In this article, Ciafaloni et al. analyzed the asymptotic behaviour of deep inelastic processes in the semi-hard region x→0, where the angles between incoming and outgoing partons are ordered.
402 citations
TL;DR: In this paper, the authors use the techniques of an effective field theory for heavy quark systems to calculate lepton energy distributions in heavy meson decays, and show that there are no nonperturbative corrections of order mbΛQCD to the average invariant mass-squared of the final hadronic state.
352 citations
TL;DR: In this paper, the gluon and antiquark distributions of the nucleon are generated radiatively using the assumption that at some low resolution scale the nucleus consists entirely of valence quarks and valence-like gluons and simple parametrizations of the resulting (positive definite!) parton distributions are presented in the range 10−4≲x≦1 and 0.2≲Q2 ≲106 GeV2.
Abstract: The gluon and antiquark distributions of the nucleon are generated radiatively using the assumption that at some low resolution scale the nucleon consists entirely of valence quarks and valence-like gluons. The agreement between the uniquely predicted gluon and sea distributions and the available data on deep inelastic structure functions (including also recent low-Q2 measurements) and direct-photon production is demonstrated and discussed in detail. Simple parametrizations of the resulting (positive definite!) parton distributions are presented in the range 10−4≲x≦1 and 0.2≲Q2≲106 GeV2 as obtained according to the leading- and higher-order renormalization group evolution equations.
200 citations
TL;DR: In this paper, the transverse spin asymmetry of a quark in a baryon and the linear polarization of a gluon in a vector meson are studied from thet-channel point of view.
Abstract: The transverse spin asymmetry of a quark in a baryon and the linear polarization of a gluon in a vector meson are studied from thet-channel point of view. Using the Altarelli-Parisi approach, they are shown to obey independent evolution equations and to decrease with increasingQ2. We investigate the possibility to measure them at leading twist, to leading order in α and αs and without analyzing the final polarizations. This requires simultaneous polarization of the beam and the target; the observable effect is in the azimuthal distribution of the highPT particle or jet. Assuming a simple (quark+scalar diquark) model for the baryon, a large asymmetry is expected inp\(\bar p\) Drell-Yan collisions, a smaller one in highPTpp collisions, from the interference term in the scattering of two identical quarks.
158 citations
TL;DR: A next-to-leading-order QCD structure-function analysis of deep-inelastic muon and neutrino scattering data is presented and tighter constraints on the quark and gluon distributions are placed.
Abstract: We present a next-to-leading-order QCD structure-function analysis of deep-inelastic muon and neutrino scattering data. In particular, we incorporate new $\frac{{F}_{2}^{\ensuremath{\mu}n}}{{F}_{2}^{\ensuremath{\mu}p}}$ data and take account of a recent reanalysis of SLAC data. The fit is performed simultaneously with next-to-leading-order fits to recent prompt photon and Drell-Yan data. As a result we are able to place tighter constraints on the quark and gluon distributions. Two definitive sets of parton distributions are presented according to whether the European Muon Collaboration or Bologna-CERN-Dubna-Munich-Saclay Collaboration muon data are included in the global fit. Comparisons with distributions obtained in earlier analyses are made and the consistency of data sets is investigated.
123 citations
TL;DR: In this article, power corrections to ∫dx g1(x) and second moments∫dx x2g2(x), respectively, are calculated in the framework of QCD sum rules.
116 citations
CERN1
TL;DR: In this article, a simple and rigorous derivation of a recently proposed generalisation of the Goldberger-Treiman relation is presented, and its renormalisation group properties are discussed. And separately isospin-conserving quark and gluon components of the proton spin are defined.
91 citations
TL;DR: In this article, high statistics data on the structure functions F2 of the proton and the deutron measured with the same apparatus in deep inelastic muon scattering are used to study the ratio of structure functions of neutron and proton F2n/F2p and their difference F2p-F2n.
87 citations
01 Dec 1990
TL;DR: In this paper, a standard jet definition for QCD measurements involving light quarks and gluons is proposed, which involves the use of cone in the {eta} - {phi} metric with a radius of 0.7 units.
Abstract: In order to reduce uncertainties in the comparison of jet cross section measurements, we are proposing a standard jet definition to be adopted for QCD measurements involving light quarks and gluons. This definition involves the use of cone in the {eta} -- {phi} metric with a radius of 0.7 units.
72 citations
TL;DR: The size of the gluonic contribution to the first moment of {italmore » g}{sub 1} is entirely a matter of the convention used in defining the quark distributions.
Abstract: We examine the suggestion of Altarelli and Ross and of Carlitz, Collins, and Mueller that there is a hard gluonic contribution to the first moment of the proton's spin-dependent structure function {ital g}{sub 1}. We find that if the soft (collinear) divergence in the gluonic contribution is regulated dimensionally or with a quark mass, then the first moment vanishes. More generally, we suggest that the hard gluonic contribution to {ital g}{sub 1} be identified by subtracting certain contributions that are attributable to the spin-dependent quark distributions. We show that the first moment of the resulting hard gluonic contribution vanishes, provided that the UV regulator for the spin-dependent quark distributions respects gauge invariance, Lorentz invariance, and the analyticity structure of the unregulated distributions. However, by relaxing the Lorentz-invariance requirement, we are able to construct quark distributions such that the hard gluonic contribution to the first moment of {ital g}{sub 1} is nonzero. The corresponding quark distributions are related to matrix elements of Lorentz-variant operators. Hence, they have no analogue in the standard operator-product expansion and do not satisfy the usual forms of the quark sum rules. We conclude that the size of the gluonic contribution to the first moment of {italmore » g}{sub 1} is entirely a matter of the convention used in defining the quark distributions.« less
TL;DR: In this paper, the characteristics of B meson semileptonic decays into τν τ in a two Higgs doublet model were discussed and the energy spectrum and the polarization of the τ - lepton were significantly modified in a scenario with a hierarchy of the vacuum expectation values of the Higgs fields.
TL;DR: In this paper, a spin-dependent parton distribution with radiatively generated predictions for ΔG(x, Q)2, compatible with recent data, and for the gluon asymmetry was presented satisfying the available experimental and theoretical constraints.
TL;DR: In this article, the anomalous contribution of both perturbative and nonperturbative gluon configurations and the helicity of hard gluons measured in high-energy inclusive scattering is analyzed.
TL;DR: The log-normal distribution as discussed by the authors is a simple parametrization of multiplicities in hadron-hadron minimum bias scattering and it fits data at all available energies, including the highest energy (p p at s =900 GeV ).
University of California, Berkeley1, University of California, Santa Barbara2, University of Massachusetts Amherst3, SLAC National Accelerator Laboratory4, University of California, Los Angeles5, Iowa State University6, University of California, Riverside7, University of California8, Max Planck Society9, University of California, San Diego10, University of California, Davis11
TL;DR: The TPC/Two-Gamma Collaboration has measured the cross section for production of charmed D∗± mesons in photon-photon collisions as mentioned in this paper, and the result, σ(e + e − → e + e - D ∗± X) = 74±26±19 pb, is in agreement with the quark parton mo del prediction for e+e- → e+ e-c c, combined with a Lund model for the hadronization of the charmed quarks.
TL;DR: In this paper, the authors investigated the double parton scattering production of W±+jets in proton colliders and showed that at high energies an observable signal is expected from doubleparton collisions when events with small transverse momentumW together with two jets balancing inpT are selected.
Abstract: We investigate the double parton scattering production ofW±+jets in proton colliders. At high energies an observable signal is expected from double parton collisions when events with small transverse momentumW together with two jets balancing inpT are selected. Double parton scattering is also a potentially serious background to several rare processes whose signal is aW++W−(→ev+jets) final state. A simplepTW cut seems to be sufficient to separate the genuineW-pair events from the double scattering background.
TL;DR: In this article, the production of open QQ (Q=c or b) as well as of heavy quarkonia in proton-proton collisions with polarized beam and target is considered.
TL;DR: In this article, it was shown that α s is sensitive to the cut-off for the perturbative QCD cascade, i.e., if α s grows like 1 1 n (k ⊥ 2 /Λ 2 ) then the state becomes too chaotic.
TL;DR: The dual parton model (DPM) is very successful in describing hadronic multiparticle production and is formulated in the form of a Monte Carlo event generator.
Abstract: The dual parton model (DPM) is very successful in describing hadronic multiparticle production. The version of DPM presented includes both soft and hard mechanisms. The hard component is described according to the lowest-order perturbative QCD-parton-model cross section. The model is formulated in the form of a Monte Carlo event generator. Results obtained with this event generator are compared with data on inclusive reactions in the TeV energy range of the CERN and Fermilab hadron colliders.
CERN1
TL;DR: In this article, the relation between the light-cone expansion and the QCD improved parton model formalism for polarized deep inelastic muon production is discussed in detail, and the regulator dependence of the relevant quantities is explicity studied at the two-loop level for the first moment ofg1P.
Abstract: The relation between the light-cone expansion and the QCD improved parton model formalism for polarized deep inelastic muon-production is discussed in detail. The regulator dependence of the relevant quantities is explicity studied at the two-loop level for the first moment ofg1P. It is shown that the anomalous gluon component is well defined if the quark term is specified as a conserved quantity that does not evolve inQ2. The behaviour of the first moment ofg1P at the threshold for heavy quark production is also discussed.
TL;DR: In this paper, higher-order contributions to various QCD processes are considered and the terms due to the exchange of an eikonal gluon between the incoming partons are studied.
TL;DR: In this article, preliminary data from the New Muon Collaboration (NMC) allow a precise evaluation of I p−n (x)= ∫ x 1 x′ −1 dx′[F p 2 (x′) − F n 2 (n 2 ) for values of x down to 0.004.
TL;DR: In this paper, a review of colliding hadrons with high transverse momenta is presented, with a focus on the effect of the colliding beams on the dynamics of constituent scattering.
TL;DR: The unitarization of the cross section is achieved, accounting for all semihard partonic scatterings, namely, including both disconnected collisions and rescatterings, and the energy distribution of the scattered partons turns out to be a regular function of the cutoff {ital p}{sub {ital t}}{sup min} which separatesSemihard events from soft ones.
Abstract: The energy spectrum from semihard partonic interactions in nucleus-nucleus collisions with c.m. energies of the order of 1 TeV per nucleon is discussed. The presence of a large number of nucleons induces incoherence among most of the partonic collisions, while the large number of partonic interactions makes the unitarization of the cross section an essential tool for a meaningful description of the processes. This goal is achieved, accounting for all semihard partonic scatterings, namely, including both disconnected collisions and rescatterings. The characteristic feature of the interaction resulting from this analysis is that it is basically a geometrical one. As a consequence of the unitarization, the energy distribution of the scattered partons turns out to be a regular function of the cutoff ${\mathit{p}}_{\mathit{t}}^{\mathrm{min}}$ which separates semihard events from soft ones.
TL;DR: In this article, an updated version of the Monte Carlo program COJETS is presented, which simulates p -p and p-p interactions at high energy, including particles with charm, bottom and top.
TL;DR: In this paper, a detailed analysis of the initial number of gluons and quarks in the generalized multiplicity distribution (GMD) is presented, and two special cases of GMD, namely, the negative binomial distribution and the Furry-Yule distribution, are also discussed in relation to the non-single-diffractive data at 200, 546, and 900 GeV c.m. energies and pseudorapidity intervals.
Abstract: A detailed analysis of the behavior of the initial numbers of gluons and quarks in the generalized multiplicity distribution (GMD) is presented. Two special cases of GMD, namely, the negative-binomial distribution and the Furry-Yule distribution, are also discussed in relation to the non-single-diffractive data at 200, 546, and 900 GeV c.m.-system energies and pseudorapidity intervals ${\ensuremath{\eta}}_{c}$. The GMD may provide an alternate distribution to understand parton action for future $p\overline{p}$ collisions at high TeV energies.
TL;DR: In this article, the size of the gluon distribution at small x has important implications for phenomenology at future high energy hadronhadron and lepton-hadron colliders.
TL;DR: In this paper, a phenomenological model of spin sharing by the constituents of a proton is constructed, based on the recent EMC measurement of the spin dependent structure function and knowledge of the unpolarized parton densities.
Abstract: A phenomenological model of spin sharing by the constituents of a proton is constructed, based on the recent EMC measurement of the spin dependent structure function and knowledge of the unpolarized parton densities.
TL;DR: In this article, shadowing corrections to gluon and quark distributions in nuclei in the region of small values of x are discussed, which are related to parton distributions in a pomeron which are in principle measurable in hard diffractive processes on the nucleon target.
Abstract: The shadowing corrections to gluon and quark distributions in nuclei in the region of small values ofx are discussed They are related to parton distributions in a pomeron which are in principle measurable in hard diffractive processes on the nucleon target Multiple scattering corrections to shadowing are considered in a model dependent way The perturbative QCD evolution of shadowing is also taken into account Various possibilities of the partonic content of a pomeron are considered It is shown in particular that the conventional parametrizations of parton distributions in a pomeron which are based on the assumption that it consists mostly of gluons imply substantial nuclear shadowing in gluon distributions in heavy nuclei Possible phenomenological implications of shadowing corrections in nuclear parton distributions for various semi-hard processes with nuclear targets are briefly discussed