Improved Q2-Rescaling Model and the Nuclear Effect of Parton Distribution Functions

Considering that the original Q²-rescaling model has some shortcomings in explaining the experimental data,we propose animproved Q²-rescaling model in which,in order to compensate for the loss of nuclear momentum,we employ different Q²-rescaling parameters for momentum distributions of valence quark,sea quark and glouns.By using improved Q²-rescaling model,We can well explain the experimental data of the EMC effect in the whole x region,the nuclear Drell-Yan Process and J/ψ photoproduction process.     

Quark distributions in nuclei and nuclear effects on nucleon structure functions

Extended quark distribution functions are presented obtained by fitting a large amount of experimental data of the l-A DIS process on the basis of an improved nuclear density model. The experimental data of l-A DIS processes with A≥3 in the region 0.0010≤x≤0.9500 are quite satisfactorily described by using the extended formulae. Our knowledge of the influence of nuclear matter on the quark distributions is deepened.     

Quark distributions in nuclei and nuclear effects on nucleon structure functions

Extended quark distribution functions are presented obtained by fitting a large amount of experi-mental data of the ι-A DIS process on the basis of an improved nuclear density model. The experimental data of ι-A DIS processes with A≥ 3 in the region 0.0010 ≤ x ≤ 0.9500 are quite satisfactorily described by using the extended formulae. Our knowledge of the influence of nuclear matter on the quark distributions is deepened.     

改进的核密度模型与轻子-核DIS过程中的核效应

提出了改进的核密度模型, 用唯象的方法找到了束缚核子内价夸克和海夸克的 核效应的参数公式, 其中利用了我们已经建立的核密度与原子核的平均结合能 之间的联系. 利用该模型所得到的束缚核子内部分子分布函数, 对轻子与核 的DIS(深度非弹性散射)过程的核效应给出了满意的解释, 深化了对原子核内夸克分布受核效应影响的认识.     

推广x重新标度模型重标度参数公式与轻子-核DIS过程的核效应

与原子核的平均结合能相联系，给出了部分子的推广x重新标度模型的重标度参数公式.利用该公式给出的重标度参数值，计算了铝核、钙核、铅核分别与碳核DIS过程的平均结构函数之比，结果表明理论计算与实验数据符合较好.     

QCD非微扰和能量丢失效应对夸克分布影响

在非常数性K因子的情况下,根据核Drell-Yan过程的高能强子h同原子核A碰撞和高能轻子l同原子核A深度非弹性碰撞的实验数据,在考虑QCD非微扰效应对深度非弹性散射部分子分布的影响及Drell-Yan过程中的能量丢失效应,计算确定价夸克分布和海夸克分布核效应函数RAυ(x₂),RAS(x₂)的变化,深化了对原子核内夸克分布受核效应影响的认识     

改进的双重Q~2重标度模型

提出了改进的双重Q2重标度模型,在保持核动量守恒的条件下,用唯象的方法找到了一套重标度参数公式,建立了重标度参数ξv,ξs及ξg与原子核平均结合能之间的联系.利用该模型所得到的束缚核子内部分子分布函数,对核DIS过程,核Drell-Yan过程和J/Ψ光生过程均给出满意的解释.     

Saturation of nuclear partons: Fermi statistics or nuclear opacity?

We derive the two-plateau momentum distribution of final state (FS) quarks produced in deep inelastic scattering (DIS) off nuclei in the saturation regime. The diffractive plateau, which dominates for small p, measures precisely the momentum distribution of quarks in the beam photon; the role of the nucleus is simply to provide an opacity. The plateau for truly inelastic DIS exhibits a substantial nuclear broadening of the FS momentum distribution. We discuss the relationship between the FS quark densities and the properly defined initial state (IS) nuclear quark densities. The Weizsäcker-Williams glue of a nucleus exhibits a substantial nuclear dilution, still soft IS nuclear sea saturates because of the anti-collinear splitting of gluons into sea quarks.     

改进的双重Q2重标度模型

提出了改进的双重Q²重标度模型,在保持核动量守恒的条件下,用唯象的方法找到了一套重标度参数公式,建立了重标度参数ξ_v,ξ_s及ξ_g与原子核平均结合能之间的联系.利用该模型所得到的束缚核子内部分子分布函数,对核DIS过程,核Drell-Yan过程和J/Ψ光生过程均给出满意的解释 关键词： 2重标度模型')" href="#">双重Q²重标度模型 核效应 结合能     

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.     

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     

Quark Orbital Angular Momentum

Generalized parton distributions provide information on the distribution of quarks in impact parameter space. For transversely polarized nucleons, these impact parameter distributions are transversely distorted and this deviation from axial symmetry leads on average to a net transverse force from the spectators on the active quark in a DIS experiment. This force when acting along the whole trajectory of the active quark leads to transverse single-spin asymmetries. For a longitudinally polarized nucleon target, the transverse force implies a torque acting on the quark orbital angular momentum (OAM). The resulting change in OAM as the quark leaves the target equals the difference between the Jaffe–Manohar and Ji OAMs.     

手征胶子修正夸克平均场模型

这项工作利用考虑π介子与胶子效应的夸克平均场模型研究原子核结构的基本性质。在夸克平均场中,核子由三个束缚在谐振子势场中的组分夸克构成。描述强相互作用的量子色动力学必须满足手征对称性,此外夸克之间也需要通过交换胶子相互作用。因此,在夸克平均场模型中,对利用夸克势获得的核子质量考虑π介子修正与胶子修正。通过少数稳定有限核的结合能与半径实验值确定模型中的未知参数,获得了一组夸克平均场相互作用参数,QMF-NK。利用该组参数计算40Ca和208Pb的电荷密度分布,发现与实验值符合很好。随后获得了与经验值一致的对称核物质的饱和性质。包含π介子修正和胶子修正的夸克平均场模型能够更好地描述有限核和核物质的性质。The basic properties of nuclear structure are studied within the quark mean field (QMF) model by taking the effects of pions and gluons into account. In QMF, the nucleon is made up of three constituent quarks confined by a harmonic oscillator potential. The quantum chromodynamics describing the strong interaction must satisfy the chiral symmetry and quarks interact with each other through exchange of gluons. Therefore pion correction and gluon correction are included in the nucleon mass obtained by using quark confinement potential in quark mean field model. We determine the unknown parameters in the model by fitting the experimental data of the binding energies and radii of several stable finite nuclei and obtain a set of parameters of quark mean field interaction, named QMF-NK. The charge density distributions of 40Ca and 208Pb are calculated, which are in good agreement with the experimental data. Later the saturation properties of symmetric nuclear matter which are consistent with the empirical data are obtained. With the pion and gluon corrections, the QMF model could treat finite nuclei and nuclear matter better.     

Q2-Rescaling Parameters’Empiric Formula of the Double Q2-Rescaling Model

We presented a Q²-rescaling parameters′empiric formula of the Q²-rescaling model, in which we established the connection between the Q²-rescaling parameters ξ_i(i=V,S,G) and the mean binding energy in nucleus. By using the formula, we can get the Q²-rescaling parameters for various nuclei with A>12, and thus further calculate the relevant nuclear process and make out prediction.     

Quark-antiquark recombination in the fragmentation region

Meson production at low transverse momentum in the fragmentation region (x>0.5) in pp collisions is considered in the context of the parton model. It is shown that the quark decay process is unimportant compared to the quark-antiquark recombination process. The calculated results of the model agree very well with the experimental data on the longitudinal momentum distributions of π^± and K^± in both the shapes and the normalizations.     

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.