Quark Energy Loss and Shadowing in Nuclear Drell-Yan Process

The energy loss effect in nuclear matter is another nuclear effect apart from the nuclear effects on the parton distribution as in deep inelastic scattering process. The quark energy loss can be measured best by the nuclear dependence of the high energy nuclear Drell-Yan process. By means of three kinds of quark energy loss parameterizations given in literature and the nuclear parton distribution extracted only with lepton-nucleus deep inelastic scattering experimental data, measured Drell-Yan production cross sections are analyzed for 800 GeV proton incident on a variety of nuclear targets from FNAL E866. It is shown that our results with considering the energy loss effect are much different from those of the FNAL E866, who analyzes the experimental data with the nuclear parton distribution functions obtained by using the deep inelastic IA collisions and pA nuclear Drell-Yan data. Considering the existence of energy loss effect in Drell-Yan lepton pairs production, we suggest that the extraction of nuclear parton distribution functions should not include Drell-Yan experimental data.     

Quark Energy Loss and Shadowing in Nuclear Drell-Yan Process

The energy loss effect in nuclear matter is another nuclear effect apart from the nuclear effects on the parton distribution as in deep inelastic scattering process. The quark energy loss can be measured best by the nuclear dependence of the high energy nuclear Dre11-Yan process. By means of three kinds of quark energy loss parameterizations given in literature and the nuclear parton distribution extracted only with lepton-nucleus deep inelastic scattering experimental data, measured Dre11-Yan production cross sections are analyzed for 800 GeV proton incident on a variety of nuclear targets from FNAL E866. It is shown that our results with considering the energy loss effect are much different from those of the FNAL E866, who analyzes the experimental data with the nuclear parton distribution functions obtained by using the deep inelastic IA collisions and pA nuclear Drell-Yan data. Considering the existence of energy loss effect in Drell-Yan lepton pairs production, we suggest that the extraction of nuclear parton distribution functions shoul““““d not include Dre11-Yan experimental data.     

Nuclear parton distribution functions and energy-loss effect in the Drell-Yan reaction off nuclei

The energy-loss effect in nuclear matter is another nuclear effect apart from the nuclear effects on the parton distribution as in deep inelastic scattering process. The quark energy loss can be measured best by the nuclear dependence of the high energy nuclear Drell-Yan process. By means of two typical kinds of quark energy-loss parametrization and the different sets of nuclear parton distribution functions, we present an analysis of the E866 experiments on the nuclear dependence of Drell-Yan lepton pair production resulting from the bombardment of Be, Fe and W targets by 800 GeV protons at Fermilab. It is found that the quark energy loss in cold nuclei is strongly dependent on the used nuclear parton distribution functions. The further prospects of using relatively low energy protons incident on nuclear targets are presented by combining the quark energy-loss rate determined from a fit to the E866 nuclear-dependent ratios versus x ₁, with the nuclear parton distribution functions given from lA deep inelastic scattering (DIS) data. The experimental study of the relatively low energy nuclear Drell-Yan process can give valuable insight in the energy loss of the fast quark propagating through cold nuclei and help to pin down nuclear parton distribution functions.Received: 8 September 2004, Revised: 18 October 2004, Published online: 11 January 2005PACS: 24.85. + p, 13.85.Qk, 25.40.-h, 25.75.Nq     

Excess pions in Drell-Yan and deep inelastic scattering experiments

Recent data on Drell-Yan processes induced by protons on nuclear targets gives non trivial information about nuclear effects. A very simple model for excess pions in nuclei reproduces the main features of these data, and also of those comming from deep inelastic experiments. This simple scheme gives an unified treatement of nuclear effects highlighting its importance in the deuteron and provides a precise prediction for futurep-p andp-d Drell-Yan experiments.     

Experimental cross section for dimuon production and the Drell-Yan model

We have measured the absolute cross section for dimuon production in hadron collisions at 200 GeV/c in the continuum region M = 4–8.5 GeV. In all the channels studied (pN, $\text{p}$N, π^±N and π^?H₂) the experimental cross section is significantly larger by a factor of 2.3 ± 0.5 than expected from the Drell-Yan model. Furthermore, our proton-nucleon data allow a determination of the nucleon valence structure function which agrees with the deep inelastic lepton scattering data.     

Two-photon collisions in deep inelastic lepton-nucleon and lepton-nucleus scattering

We have calculated the μ-pair production via photon-photon collisions in deep-inelastic charged lepton scattering on proton and nuclei, using the equivalent photon approximation. Specific parametrizations were assumed for the proton and the nuclei form factors and the QED photon structure function. Results are given for lepton energies below 300 GeV and virtual photon massesQ ² less than 50 GeV², as functions of the μ-pair mass, the scaling variablex and the electric chargeZ of the hadron target. Using a photon structure function derived from QPM and VDM we also estimate the contribution of γγ collisions to hadron production in these deep inelastic processes.     

Nuclear Structure in High Energy Scattering Processes

We suggest that in hard scattering processes the nuclear medium can be viewed as a background parton sea where the bound nucleons are "soaked". The quark and gluon distributions in nuclei are investigated under this assumption. The comparisons of this model with the experimental data of the structure function ratio from charged lepton deep inelastic scattering, the gluon momentum distribution ratio from inelastic J/Ψ production, and the dimuon yield ratio from Drell-Yan dimuon production are present.     

Target-mass effects in hadronic lepton-pair production

Hadronic mass corrections to the Drell-Yan formulae are calculated for on-shell partons and shown to be uniquely determined by the quark distributions extracted from deep inelastic lepton-hadron scattering experiments. It turns out that these corrections are negligible for present day experiments. Arguments in favour of on-shell partons are presented.     

Higher order QCD effects in inclusive annihilation and deep inelastic scattering

We present a parton model interpretation of the predictions of quantum chromodynamics in the process e⁺e^?→hadron + anything. We give thecomplete list of parameters needed for the study of the scaling violations of fragmentation functions up to the next-to-leading logarithmic approximation. This includes flavour non-singlet and flavour singlet anomalous dimensions up to order α² and coefficient functions up to order α. We also present results for the deep inelastic scattering e^?h→e^? + anything. We find that in e⁺e^? annihilation the ratio of scaling violations of second order to first order is in general bigger than the corresponding ratio for deep inelastic scattering. The Gribov-Lipatov relation is thus violated in second order. We also find that a modified Drell-Yan analytic continuation relation holds between the deep inelastic and annihilation structure functions for quarks and gluons. In x space we give detailed numerical evaluation of the QCD effects for non-singlet and singlet densities, in the space-like and time-like regions.     

Nuclear shadowing and Drell-Yan production on heavy nuclei

The suggestion that nuclear shadowing in deep inelastic scattering is primarily a parton phenomenon is extended to the Drell-Yan reaction on heavy nuclei. The nuclear structure functions required to describe the latter process are found to be compatible with those obtained from an analysis of the shadowing data, and lend weight to the hypothesis that this is indeed a parton phenomenon.     

Low limit on the slope ofNNπ andNΔπ vertex form factors from deep inelastic lepton scattering

We elaborate and update the Thomas analysis of the restrictions on thet-dependence of theNNπ andNΔπ vertex form factors originating from deep inelastic lepton-nucleon scattering. In particular in the case of the monopole parametrization we find the derived upper bound on the monopole massΛ isΛ<0.5 GeV.     

Deep inelastic scattering from the nuclear medium

We reexamine deep inelastic scattering from nuclei under assumptions commonly employed in the literature: that quarks remain confined in hadronic constituents of nuclei, that the nuclear cross section is the average of the free-space cross section of hadron i weighted by the probability of finding i in the nucleus, and that there are no final state interactions between the debris of hadron i and the rest of the nucleus. We develop a cluster expansion for the cross section of deep inelastic lepton scattering and the Drell-Yan process on nuclei. Using the “instant” from of dynamics, we find that large contributions to these processes arise from nuclear interactions and correlations. However, our theory differs in detail from other approaches, and we find that binding alone is unlikely to explain the EMC effect. Also, in contrast to many recent papers on the subject, we conclude that the contribution of pions (and other nonnucleonic consistuents of the nucleus) is strongly suppressed.     

An “effective-A” dependence of cross sections in ultra-relativistic heavy-ion collisions and its interference with quark-gluon plasma signatures

It is shown that in ultra-relativistic nucleus-nucleus collisions, as a consequence of the geometry of the collision, there is a dependence of the total and differential cross sections on effective atomic mass numbers of the target and beam nuclei. The general expressions of the effective atomic mass numbers are deduced and they are computed for 0+Cu, O+U, S+U, Si+Au and U+U collisions. This particular A-dependence of the cross sections can have a strong effect on the production ratio of two particles of different species. As a consequence it might simulate a signature of quark-gluon plasma which is expected to be given by the yields ratio of two different particles. It is shown that this effect can explain quantitatively the K/π ratios measured in Si+Au and S+W collisions as well as the decrease of the J/ψ production relative to Drell-Yan lepton pairs measured in O+Cu, O+U and S+U collisions. The need of precise measurements of the powers α and α(x_F, P_T) in inclusive nuleon-nuleus interactions for the understanding of particle production in nucleus-nucleus collisions is stressed. Expectations for future experiments are presented.     

Nuclear shadowing and heavy-ion collisions at high energies

Nuclear shadowing effects for quarks and gluons are calculated using information on diffractive deep inelastic scattering on a nucleon. Role of these effects in interactions of hadrons and nuclei with nuclei at high energies is investigated. A decrease in particle densities for heavy-ion collisions in comparison with the Glauber model is predicted and nuclear modification factors are calculated. Distributions of gluons in nuclei are used to predict suppression of heavy quarkonia. The parameter-free calculation of J/ψ in DAu and AuAu collisions is in a good agreement with recent RHIC data. Predictions for heavy quarkonia suppression in heavy-ion collisions at LHC are formulated.     

Implications of new deep inelastic scattering data for parton distributions

We perform a next-to-leading order structure function analysis of μN and νN deep inelastic data in an attempt to resolve the disagreement between recent EMC and BCDMS measurements of F₂ for μp scattering. Equally acceptable QCD fits are obtained including either set of μN data, but a comparison with Drell-Yan data appears to favour the parton distributions derived from the BCDMS data.     

On the Nuclear Effects of Valence Quark Distributions and Sea Quark Distributions

In this paper we present a method which may be used to get the nuclear effect functions R_υ^A(x_t) and R_s^A(x_t) for valence quark distributions and sea quark distributions in the light of the data of 1-A deep inelastic scattering and nuclear Drell-Yan process. Both the functions may be used to test the theoretical models explaining the nuclear effects. With nuclei Fe, Ca and C as examples, the results are shown.     

Influence of quark energy loss on extracting nuclear sea quark distribution from nuclear Drell-Yan experimental data

By means of two typical kinds of quark energy loss parametrization and the nuclear parton distributions determined only with lepton-nuclear deep inelastic scattering experimental data, a leading order analysis is performed on the proton-induced Drell-Yan differential cross section ratios of tungsten versus deuterium as a function of the quark momentum fraction in the beam proton and target nuclei. It is found that the theoretical results with quark energy loss are in good agreement with the experimental data. The quark energy loss effect produces approximately 3% to 11% suppression on the Drell-Yan differential cross section ratios R_W/D in the range 0.05≤x₂≤0.3. The application of nuclear Drell-Yan data with heavy targets is remarkably subject to difficulty in the constraint of the nuclear sea quark distribution.     

Suppression of charmonium production in PbPb collisions at 158 GeV/c per nucleon and quark-gluon deconfinement

An anomalous suppression of the charmonium yield in central collisions was observed in studying charmonium production in collisions of Pb nuclei accelerated to a momentum of 158 GeV/c per nucleon with Pb target nuclei. It is shown that, in peripheral collisions, the ratio of the cross section for J/ψ production to the cross section for the Drell-Yan process decreases exponentially (as in the case of collisions of lighter nuclei) owing to the ordinary absorption of J/gy in nuclear matter. The observed threshold effect of the anomalous suppression of charmonium production agrees well with the predictions based on the assumption of Debye color screening in the formation of quark-gluon plasma.