核环境中部分子演化与重组效应下的核内胶子分布

在既考虑到泄漏在束缚核子外的海夸克与胶子间的重组,又考虑到仍束缚在核子内的部分子由于其禁闭空间的变化而发生的演化的基础上,给出了核内胶子分布函数的普遍形式,并具体计算了锡梭与碳核的胶子分布比,结果与NMC实验合作组的最新实验相一致.     

Small x phenomenology on gluon evolution through the BFKL equation in light of a constraint in multi-Regge kinematics

We investigate the impact of so-called kinematic constraint on gluon evolution at small x.Implanting the constraint on the real emission term of the gluon ladder diagram, we obtain an integro-differential form of the Balitsky-Fadin-Kuraev-Lipatov(BFKL) equation. Later we solve the equation analytically using the method of characteristics. We sketch the Bjorken x and transverse momentum k_t~2 dependence of our solution of unintegrated gluon distributions f (x,k_t~2) in the kinematic constraint supplemented BFKL equation and contrasted the same with the original BFKL equation. Then we extract the integrated gluon density xg(x, Q~2) from unintegrated gluon distributions f (x,k_t~2) and compared our theoretical prediction with that of global data fits, namely NNPDF3.1 sx and CT14. Finally we illustrate the phenomenological implication of our solution for unintegrated gluon distribution f (x,k_T~2) towards exploring high precision HERA DIS data by the theoretical prediction of proton structure functions(F_2 and F_L).     

Nuclear shadowing and antishadowing in a unitarized BFKL equation

The nuclear shadowing and antishadowing effects are explained by a unitarized BFKL equation.The Q2-and x-variations of the nuclear parton distributions are detailed based on the level of the unintegrated gluon distribution.In particular,the asymptotical behavior of the unintegrated gluon distribution near the saturation limit in nuclear targets is studied. Our results in the nuclear targets are insensitive to the input distributions if the parameters are fixed by the data of a flee proton.     

A Test of Color-Octet Heavy Quarkonium Production Mechanism

Using the scale evolution of nuclear parton distributions,the contribution of color-octet heavy quarkonium production mechanism to the P Fe → J/ψ γ X process in calculated and discussed.Comparing our theoretical results with the future experimental data,the color-octet heavy quarkonium production mechanism can be examined.``     

Nuclear shadowing and antishadowing in a unitarized BFKL equation

The nuclear shadowing and antishadowing effects are explained by a unitarized BFKL equation. The Q²- and x-variations of the nuclear parton distributions are detailed based on the level of the unintegrated gluon distribution. In particular, the asymptotical behavior of the unintegrated gluon distribution near the saturation limit in nuclear targets is studied. Our results in the nuclear targets are insensitive to the input distributions if the parameters are fixed by the data of a free proton.     

A Test of Color-Octet Heavy Quarkonium Production Mechanism

Using the scale evolution of nuclear parton distributions,the contribution of color-octet heavy quarkonium production mechanism to the P + Fe → J/ψ + γ + X process in calculated and discussed.Comparing our theoretical results with the future experimental data,the color-octet heavy quarkonium production mechanism can be examined.     

Nuclear PDFs at NLO – status report and review of the EPS09 results

We review the current status of the global DGLAP analysis of nuclear parton distribution functions, nPDFs, focusing on the recent EPS09 analysis [K.J. Eskola, H. Paukkunen, C.A. Salgado, JHEP 0904 (2009) 065. [arXiv:0902.4154 [hep-ph]]], whose output, EPS09NLO, is the best-constrained NLO nPDF set on the market. Collinear factorization is found to work very well in the kinematical region studied. With the error sets released in the EPS09 package one can compute how the nPDF-related uncertainties propagate into factorizable nuclear hard-process cross sections. A comparison with the other existing NLO nPDF sets is shown, and the BRAHMS forward-η hadron data from d+Au collisions are discussed in the light of the EPS09 nPDFs and their error sets.     

Regularization dependence of pion generalized parton distributions

Pion generalized parton distributions are calculated within the framework of the Nambu–Jona-Lasinio model using different regularization schemes, including the proper time regularization scheme, the three-dimensional (3D) momentum cutoff scheme, the four-dimensional momentum cutoff scheme, and the Pauli-Villars regularization scheme. Furthermore, we check the theoretical constraints of pion generalized parton distributions required by the symmetries of quantum chromodynamics in different regularization schemes. The diagrams of pion parton distribution functions are plotted, in addition, we evaluate the Mellin moments of generalized parton distributions, which are related to the electromagnetic and gravitational form factors of pion. Pion generalized parton distributions are continuous but not differential at begin{document}$ x=pm ,xi $end{document}, when considering the effect of the contact contribution term, generalized parton distributions become not continuous at begin{document}$ x=pm ,xi $end{document} in all the four regularization schemes. Generalized parton distributions in impact parameter space are considered, the width distribution of u quark in the pion and the mean-squared begin{document}$ langle {boldsymbol{b}}_{bot}^2rangle_{pi}^u $end{document} are calculated. The light-front transverse-spin distributions are studied when quark polarized in the light-front-transverse begin{document}$ +,x $end{document} direction, the transverse-spin density is no longer symmetric around begin{document}$ (b_x=0,b_y=0) $end{document}, the peaks shift to begin{document}$ (b_x=0,b_y>0) $end{document}, we compare the average transverse shift begin{document}$ langle b_{bot}^yrangle_1^u $end{document} and begin{document}$ langle b_{bot}^yrangle_2^u $end{document} in different regularization schemes. The light-cone energy radius begin{document}$ r_{E,LC} $end{document} and the light-cone charge radius begin{document}$ r_{c,LC} $end{document} are also evaluated, we found that in the proper time regularization scheme the values of these quantities were the largest, in the 3D momentum cutoff scheme they were the smallest.     

Cold Nuclear Matter Effects on Isolated Prompt Photon and Isolated Prompt Photon+Jet Productions in Relativistic Heavy-Ion Collisions

We investigate the cold nuclear matter(CNM) effects on isolated prompt photon and isolated prompt photon associated jet productions in nuclear collisions at the NLO accuracy by using the EPS09 NLO nuclear parton distribution functions and their error sets.Nuclear modification factors of isolated prompt photon and isolated prompt photon+jet productions due to CNM effects in p+A and A+A reactions at the RHIC and the LHC are provided with varying rapidity and transverse momentum of the final state photon.It is shown that the CNM effects on isolated prompt photon and photon+jet are modest,which give a small enhancement at low pT region and a more obvious suppression at large pT at central rapidity.At forward rapidity a pronounced suppression of γ as well as γ+jet is always observed.     

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.     

能量损失效应引起的核Drell-Yan微分截面比的压低

核环境中夸克的能量损失可以通过高能核Drell-Yan过程的核依赖进行测量. 利用文献中给出的夸克能量损失公式和从轻子－原子核深度非弹性散射实验数 据得到的束缚核子中的部分子分布函数, 计算了FNAL E772 800GeV的质子打击不同原子核的Drell-Yan过程截面比, 发现考虑能量损失的计算结果与FNAL E772实验数据符合甚好. 建议在利用核Drell-Yan过程实验数据抽取束缚核子内部分子分布函数时应该考虑能量损失效应.     

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 Effect Study Under K Factor‘s Nonconstancy

A consistent approach to estimating nuclear effect functions RA RvA (x2) and RSA(x2) based on numerical iteration technique is presented in the quark-parton model when taking into account the nonconstancy of quantum chromodynamics correction factor K. ARv (x2) and RsA(x2) correspond respectively to the valence quark distributions for one bound nucleon within the nucleus and to the sea quark ones. Related numerical analysis is given for nuclei 6 12C,20 40Ca, and 26 56Fe. As the basis, it adopts both experimental data of the high energy proton-nucleus Drell-Yan process and of the high energy lepton-nucleus deep inelastic scattering.     

Nuclear Effect Study Under K Factor's Nonconstancy

A consistent approach to estimating nuclear effect functions R_v^A(x₂) and R_s^A(x₂) based on numerical iteration technique is presented in the quark-parton model when taking into account the nonconstancy of quantum chromodynamics correction factor K. R_v^A(x₂) and R_s^A(x₂) correspond respectively to the valence quark distributions for one bound nucleon within the nucleus and to the sea quark ones. Related numerical analysis is given for nuclei ₆C¹², ₂₀Ca⁴⁰, and ₂₆Fe⁵⁶. As the basis, it adopts both experimental data of the high energy proton-nucleus Drell-Yan process and of the high energy lepton-nucleus deep inelastic scattering.     

Sigma Meson Production in Nuclear Reactions

The sigma meson production in p ＋ ^12C and p A- ^40Ca reactions at the incident energy Ep = 1.5 GeV is investigated within the Quantum Molecular Dynamics model. The simulation results indicate a distinctive A dependence of the sigma production, that is, the increase of A is followed by an increase of the production cross sections. We find that the σ meson production in proton-induced reactions is strongly medium-dependent, and the produced σ mesons decaying in a denser medium experience a stronger mass shift towards lower masses. This mass shift is an experimentally accessible observable in the final state pion pairs, which do not suffer from reabsorption by the surrounding nucleons. It is pointed out that the ratio of measured sigma cross sections as a function of the sigma invariant-mass from various reactions is a good probe to explore the existence of the σ meson in a dense nuclear environment.     

Collective Perspective on Advances in Dyson–Schwinger Equation QCD

We survey contemporary studies of hadrons and strongly interacting quarks using QCD's Dyson-Schwinger equations, addressing the following aspects: confinement and dynamical chiral symmetry breaking; the hadron spectrum; hadron elastic and transition form factors, from small-to large-Q2; parton distribution functions; the physics of hadrons containing one or more heavy quarks; and properties of the quark gluon plasma.     

Collective Perspective on Advances in Dyson-Schwinger Equation QCD

We survey contemporary studies of hadrons and strongly interacting quarks using QCD's Dyson-Schwinger equations, addressing the following aspects: confinement and dynamical chiral symmetry breaking; the hadron spectrum; hadron elastic and transition form factors, from small- to large-Q²; parton distribution functions; the physics of hadrons containing one or more heavy quarks; and properties of the quark gluon plasma.     

Chiral invariant phase space event generator

An event generator based on the CHIPS model is implemented in the GEANT4 simulation toolkit. Nuclear fragment production in the process of pion capture on nuclei is used to tune the parameters of the CHIPS model describing clusterization of nucleons in nuclei. The spectra of nucleons and nuclear fragments in pion capture and in photonuclear reactions at 60 MeV are compared with experimental data. Received: 30 May 2000 / Accepted: 2 November 2000