Colour transparency and scaling properties of nuclear shadowing in deep inelastic scattering

We present the perturbative QCD analysis of nuclear shadowing in the deep inelastic scattering at smallx in terms of the spatial wave function ofq \(\bar q\) fluctuations of virtual photons. The wave function formalism makes it quite obvious that shadowing is the scaling, rather than the higher twist, 1/Q ², effect, contrary to a numerous recent claims. We demonstrate explicitly how the scaling shadowing comes from the large, hadronic, size quarkantiquark pairs even in the limit ofQ ²→∞, and why it should very slowly, ∞1/log (Q ²/m ²) decrease at very largeQ ². We argue in favor of the scaling triple-pomeron contribution to the nuclear shadowing and present predictions for a cross section of diffraction dissociation of virtual photons and for the mass spectrum of diffraction excitation, which can be checked at HERA and Fermilab. We predict strikingly different scaling properties of diffraction dissociation and nuclear shadowing for the longitudinal and transverse photons. Our, numerial predictions for shadowing are in good agreement with the recent EMC data.     

Geometric scaling in inclusive eA reactions and nonlinear perturbative QCD

We report on geometric scaling in inclusive eA scattering data from the NMC and E665 experiments. This scaling and nuclear shadowing follows the pattern expected from nonlinear perturbative QCD for zero impact parameter at sufficiently small x(bj) and is compatible with geometric scaling in ep.     

Gluon shadowing and charmonium/bottonium production on nuclear targets

We examine the suppression ofJ/ω, ω′ and Ψ production on nuclear targets, as observed for proton and pion beams of energies from 200 to 800 GeV. We find that this suppression leads to a universal scaling curve, which indicates that it is due to nuclear modifications of the gluon density (“shadowing”). A parametrisation of the nuclear effect on the gluon density is extracted from the data and used to obtain quantitative estimates for corresponding effects in high-energy heavyion collisions.     

Interplay of soft and hard interactions in nuclear shadowing at highQ 2 and lowx

Nuclear shadowing corrections are known to be dominated by soft interactions. They grow as function of 1/x more slowly than the single scattering term, which has an essential contribution from hard interactions. Therefore, we predict that nuclear shadowing vanishes eventually at very lowx, provided thatQ ² is high and fixed. At the same time, at medium and lowQ ², nuclear shadowing grows with 1/x. Our formalism nicely explains also the recent NMC data onQ ²-dependence of the nuclear shadowing. The effect of gluon fusion is found to be of little importance for the nuclear structure function in the available range ofx. Communicated by W. Weise     

Does Shadowing Relate to Nuclear Radius?

The A-dependence of nuclear shadowing in the partonic shadowing model is analysed. We point out that the nuclear shadowing is related to the average number of shadowed nucleons rather than the nuclear radius.     

DVCS on nuclei: observability and consequences

In this paper, we discuss the feasibility of measuring deeply virtual Compton scattering (DVCS) on nuclei in a collider setting, as for example, the planned high-luminosity Electron-Ion Collider (EIC). We demonstrate that employing our recent model for nuclear generalized parton distributions (nGPDs), the one-photon unpolarized DVCS cross section as well as the azimuthal and spin asymmetry are of the same size as in the proton case. This will allow for an experimental extraction of nuclear GPDs with high precision, shedding new light not only on nuclear shadowing at small x_Bj but also on the interplay of shadowing and nuclear enhancement at .Received: 8 September 2003, Revised: 24 November 2003, Published online: 15 January 2004     

含遮蔽抛射沉积模型的有限尺寸效应

含遮蔽抛射沉积模型是在抛射沉积(BD)模型的基础上考虑了粒子以一定的角度分布倾斜入射的情况.本文应用外推方法确定了大尺寸极限下含遮蔽抛射沉积模型的各标度指数,讨论了该模型的有限尺寸效应及其标度性质.从模拟结果可以看出含遮蔽BD模型的有限尺寸效应与BD模型有所不同,遮蔽这种非局域作用可以显著地改变BD模型的标度性质. 关键词： 遮蔽效应 抛射沉积模型 有限尺寸效应 动力学标度     

Phenomenology of nuclear shadowing in deep-inelastic scattering

We investigate shadowing effects in deep-inelastic scattering from nuclei at small valuesx < 0.1 of the Bjorken variable. Unifying aspects of generalized vector meson dominance and color transparency we first develop a model for deep-inelastic scattering from free nucleons at smallx. In application to nuclear targets we find that the coherent interaction of quark-antiquark fluctuations with nucleons in a nucleus leads to the observed shadowing atx < 0.1. We compare our results with most of the recent data for a large variety of nuclei and examine in particular the Q² dependence of the shadowing effect. While the coherent interaction of low mass vector mesons causes a major part of the shadowing observed in the Q² range of current experiments, the coherent scattering of continuum quark-antiquark pairs is also important and guarantees a very weak overall Q² dependence of the effect. We also discuss shadowing in deuterium and its implications for the quark flavor structure of nucleons. Finally we comment on shadowing effects in high-energy photon-nucleus reactions with real photons.     

Diffractive production of charm in DIS and gluon nuclear shadowing

We evaluate nuclear shadowing of the total cross section of charm particles production in DIS within the framework of Gribov theory of nuclear shadowing generalized to account for the QCD evolution. We use as an input the recent QCD Pomeron parton density analysis of the HERA diffractive data. Assuming that the QCD factorization theorem is applicable to the charm production off nuclei we also calculate shadowing of the gluon densities in nuclei and find it sufficiently large for heavy nuclei: G_A~200(x,Q²)/AG_N(x,Q²) ~ 0.45 m 0.5 · (A/200)^т.15 for x ~ 10^х1ц, Q² ~ 20 1 40 GeV² to influence significantly the physics of heavy ion collisions at LHC. We evaluate also suppression of minijet and hidden charm production in the central AA collisions. We also discuss some properties of the final states for %^*A processes dominated by the scattering off small x gluons like the high p_t jet and charm production.     

Diffraction dissociation in nuclei; Application to nuclear total cross sections

We demonstrate that (i) calculations of the inelastic shadowing effect in nuclear total cross sections done to lowest order in the inelastic couplings are invalid at Fermilab energies; (ii) a recent estimate of this effect to all orders by Gribov is still too large by at least a factor six.     

Gluon shadowing in the Glauber–Gribov model

New data from the HERA experiment on (diffractive) deep inelastic scattering have been used to parameterize the nucleon and pomeron structure functions. Within the Glauber–Gribov model, the parameterizations were employed to calculate gluon shadowing for various heavy ions. We compare our results to predictions from other models. Calculations for d+Au collisions at forward rapidities at ultra-relativistic energies have been made and are compared to RHIC data on the nuclear modification factor. The results for gluon shadowing are also confronted with recent data on the nuclear modification factor at  =17.3 GeV at various values of the Feynman variable x_F, and the energy dependence of the effect is discussed. PACS 12.40.Nn; 13.60.Hb; 13.85.-t; 25.75.-q     

Inhomogeneous Shadowing Effect in High-Energy p-A Drell-Yan Process

Having studied the initial state energy loss versus nuclear shadowing for the Drell-Yan dimuon pair production in the color string model, the inhomogeneous shadowing effect is considered in this paper. We find that the inhomogeneous shadowing effect does amend the rate of energy loss per unit path length, -dE/dz. Finally, the theoretical results for the Drell-Yan differential cross-section ratios are compared with the E772 and E866 data. It is found that the theoretical results are in good agreement with the experimental data.     

Nuclear shadowing and extraction of Fp2-Fn2 at small x from deuteron collider data

We demonstrate that leading twist nuclear shadowing leads to large corrections for the extraction of the neutron structure function Fn2 from the future deuteron collider data both in the inclusive and in the tagged structure function modes. We suggest several strategies to address the extraction of Fn2 and to measure at the same time the effect of nuclear shadowing via the measurement of the distortion of the proton spectator spectrum in the semi-inclusive eD-->e'pX process.     

Nuclear shadowing effect in relativistic heavy-ion collisions

Two complementary approaches are used in studying the nuclear shadowing effect in heavy-ion collisions at SIS/GSI beam energies within a hadronic transport model. By analysing simultaneously the average transverse momentum of nucleons and pions in the reaction plane as a function of rapidity, the shadowing effect is revealed as an anticorrelation of the average transverse momentum distributions of nucleons and pions in semicentral and peripheral collisions. While by studying the azimuthal angle distribution of pions with respect to the reaction plane, the shadowing effect appears as an azimuthal anisotropy with a preferential emission of pions perpendicular to the reaction plane. The dependence of the nuclear shadowing effect on the impact parameter and the beam energy is also studied.     

Unusual effects of diffraction dissociation for multiproduction in deep inelastic scattering on nuclei

In hadron-nucleus interactions, the stronger is nuclear shadowing in the total cross section the higher is the multiplicity of secondary hadrons. In deep inelastic scattering nuclear shadowing at smallx is associated with the hadronlike behaviour of photons as contrasted to the pointlike behaviour in the non-shadowing region of largex. In this paper we predict dilution of multiproduction of secondary hadrons, and weaker fragmentation of the target nucleus, in deep inelastic leptoptoproduction on nuclei in the shadowing region of smallx as compared to the non-shadowing region of largex. This paradoxial conclusion has its origin in nuclear enhancement of the coherent diffraction dissociation of photons which affects multiproduction in the shadowing region and does not contribute in the non-shadowing region. We present numerical predictions for multiproduction in theμXe interactions studied by the Fermilab E665 collaboration.     

Phenomenology of χF Dependence of Quarkonium Production in Proton-Nucleus interactions

We present a phenomenological study of the XF dependence of quarkonium production in high-energy proton-nucleus collisions. The χ_F dependence of comover contributions is introduced to account for the observed quarkonium suppression at low χ_F. Combining comover contributions, nuclear shadowing effect, energy loss mechanism and nuclear absorption together we reproduce the overall χ_F dependence of E772/E789 data.     

Note on shadowing and diffraction in deep-inelastic lepton scattering

We discuss the close relation between shadowing in deep-inelastic lepton-nucleus scattering and diffractive photo- and leptoproduction of hadrons from free nucleons. We show that the magnitude of nuclear shadowing at small Bjorken-x, as measured by the E665 and NMC collaborations, is directly related to HERA data on the amount of diffraction in the scattering from free nucleons. Received: 16 October 1998     

Shadowing effects in nuclear parton distributions for small values ofx

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.     

改进的部分子演化模型及其对EMC效应和核Drell－Yan过程的解释

用解析方法证明了部分子演化模型可为双重Ｘ重新标度模型提供物理基础，进而利用修正的Ａｌｔｅｒａｌｌｉ－Ｐａｒｉｓｉ方程描述小ｘ区域的核遮蔽和反遮蔽效应，以改进部分子演化模型，使我们不必引入核遮蔽因子便可统一地描述ＥＭＣ效应、核遮蔽和反遮蔽效应．最后，利用改进的部分子演化模型相当好地解释了核Ｄｒｅｌｌ－Ｙａｎ过程的实验数据．