Integrated and Unintegrated Parton Distributions

We compare the twist-2 and twist-4 parton distributions both in integrated and unintegrated parton distributions. We find that when x decreases the difference between the twist-2 and twist-4 parton distributions become obvious except for the valence quark distributions. We hope the future experiments may distinguish whether the twist-4 correction is needed or not and select a reasonable unintegrated parton distribution model.     

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}^2\rangle_{\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}^y\rangle_1^u $\end{document} and \begin{document}$ \langle b_{\bot}^y\rangle_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.     

An update on the evolution of double parton distributions

We consider double parton distributions in the general case in which the virtualities of the interacting partons are different. We elaborate the corresponding evolution equations and their extension to next-to-leading logarithmic accuracy.     

Exclusive meson production at HERMES

The exclusive electroproduction of pseudoscalar and vector mesons was studied with the HERMES spectrometer at the DESY laboratory by scattering 27.6 GeV positron and electron beams off a transversely polarized hydrogen target.The results are compared to calculations based on generalized parton distributions,some of which are sensitive to the contribution of the total angular momentum of the quarks to the proton spin.     

Exclusive meson production at HERMES

The exclusive electroproduction of pseudoscalar and vector mesons was studied with the HERMES spectrometer at the DESY laboratory by scattering 27.6 GeV positron and electron beams off a transversely polarized hydrogen target.The results are compared to calculations based on generalized parton distributions,some of which are sensitive to the contribution of the total angular momentum of the quarks to the proton spin.     

Helicity-dependent generalized parton distributions in constituent quark models

Helicity-dependent generalized parton distributions of the nucleon are derived from the overlap representation of generalized parton distributions using light-cone wave functions obtained in constituent quark models. Results from two different quark models are used also to study the angular momentum sum rule and the spin asymmetry in polarized electron scattering.     

Final state interactions and the transverse structure of the pion using non-perturbative eikonal methods

In the factorized picture of semi-inclusive hadronic processes the naive time-reversal odd parton distributions exist by virtue of the gauge link which renders it color gauge invariant. The link characterizes the dynamical effect of initial/final-state interactions of the active parton due soft gluon exchanges with the target remnant. Though these interactions are non-perturbative, studies of final-state interaction have been approximated by perturbative one-gluon approximation in Abelian models. We include higher-order gluonic contributions from the gauge link by applying non-perturbative eikonal methods incorporating color degrees of freedom in a calculation of the Boer–Mulders function of the pion. Using this framework we explore under what conditions the Boer–Mulders function can be described in terms of factorization of final state interactions and a spatial distribution in impact parameter space.     

The generalized parton distribution of the pion in a relativistic Bethe-Salpeter quark model

We present a Poincaré covariant calculation of the generalized parton distribution of the pion. Results for different values of the kinematical parameters are shown and discussed.     

Working group report: Quantum chromodynamics

This is the report of the QCD working sub-group at WHEPP-8 which was part of the QCD and QGP working group. Discussion and work on some aspects of resummation and parton distribution are reported.     

Recent results from the HERMES experiment

Results are presented from the Hermes experiment which uses semi-inclusive deep inelastic lepton scattering to study the flavor structure of the nucleon.Data have been accumulated for pion and kaon double spin asymmetries,single-spin azimuthal asymmetries for meson electroproduction,deep virtual Compton scattering （DVCS）,and meson multiplicities.These results provide information on the properties of the strange sea in the proton,constraints on transverse momentum dependent quark parton distributions,and demonstrate the promise of DVCS for isolating the total angular momentum carried by the quarks in the proton.     

Recent results from the HERMES experiment

Results are presented from the Hermes experiment which uses semi-inclusive deep inelastic lepton scattering to study the flavor structure of the nucleon. Data have been accumulated for pion and kaon double spin asymmetries, single-spin azimuthal asymmetries for meson electroproduction, deep virtual Compton scattering (DVCS), and meson multiplicities. These results provide information on the properties of the strange sea in the proton, constraints on transverse momentum dependent quark parton distributions, and demonstrate the promise of DVCS for isolating the total angular momentum carried by the quarks in the proton.     

Unpolarized structure functions and the parton distributions for nucleon in an independent quark model

Considering the nucleon as consisting entirely of its valence quarks confined independently in a scalar-vector harmonic potential; unpolarized structure functions F ₁(x, μ ²) and F ₂(x, μ ²) are derived in the Bjorken limit under certain simplifying assumptions; from which valence quark distribution functions u _v(x, μ ²) and d _v(x, μ ²) are appropriately extracted satisfying the normalization constraints. QCD-evolution of these input distributions from a model scale of μ ²=0.07 GeV² to a higher Q ² scale of Q ₀ ² =15 GeV² yields xu _v(x, Q ₀ ² ) and xd _v(x, Q ₀ ² ) in good agreement with experimental data. The gluon and sea-quark distributions such as G(x, Q ₀ ² ) and q _s(x, Q ₀ ² ) are dynamically generated with a reasonable qualitative agreement with the available data; using the leading order renormalization group equations with appropriate valence-quark distributions as the input.     

Advances in diffraction of subnuclear waves

In this review, we present and discuss the most recent results on inclusive and exclusive diffractive processes at HERA and Tevatron colliders. Measurements from fixed target experiments at HERMES and Jefferson laboratory are also reviewed. The complementarity of all these results is analyzed in the context of perturbative QCD and new challenging issues in nucleon tomography are studied. A first understanding of how partons are localized in the nucleon to build orbital momenta can be addressed with these experimental results. Some prospects are outlined for new measurements in fixed target kinematic, at Jefferson laboratory and CERN, at COMPASS, or at the LHC. Of special interest is the exclusive (coherent) production of Higgs boson and heavy objects at the LHC. Based on the present knowledge, some perspectives are presented on this issue.     

Parity violation in electron scattering

By comparing the cross sections for left- and right-handed electrons scattered from various unpolarized nuclear targets, the small parity-violating asymmetry can be measured. These asymmetry data probe a wide variety of important topics, including searches for new fundamental interactions and important features of nuclear structure that cannot be studied with other probes. A special feature of these experiments is that the results are interpreted with remarkably few theoretical uncertainties, which justifies pushing the experiments to the highest possible precision. To measure the small asymmetries accurately, a number of novel experimental techniques have been developed.     

介质对部分子劈裂几率的影响

利用部分子在热密QCD介质中的辐射谱, 研究部分子在热密介质中的演化规律. 研究结果表明, 在相同能量下介质诱导效应使得部分子在介质中的劈裂几率大于部分子在真空中的劈裂几率; 高密度介质中的部分子劈裂几率大于低密度介质中的劈裂几率. 本文研究结果与美国BNL/RHIC相对论重离子碰撞实验中观测到的高横动量强子产额压低现象一致, 揭示了在RHIC能区已经生成高温高密物质.     

A New Effect in the QCD Fusion of Nuclear Partons

The parton fusion in nucleus at the leading order of recombination is investigated based on perturbative QCD. We compute various cut diagrams including the nuclear parton fusion, and find that the parton-fusion effects depend on the nuclear QCD structure.     

美国连续束电子加速器的能量升级到12GeV的科学与实验设备

驱动美国托马斯杰斐逊国家加速器装置（Thomas Jefferson National Accelerator Facility，简称JLab）的能量升级到12GeV的科学是研究胶子激发和色禁闭的起因，研究原子核的构件——核子是如何由夸克和胶子构成的，研究原子核的结构及寻找新物理等的一门科学，实验设备是12GeV的加速器、各种超导磁谱仪及极化靶等，在能量为12GeV的加速器中，将采用深度遍举过程和极化实验。     

Effect of parton cascade to medium

Jet quenching has been proposed as a probe of the properties of the strongly interacting quarkgluon-plasma in high energy heavy ion collisions.At the meantime,it is also important to study the excitation of medium by propagating jets.Based on Boltzmann equation,a Monte Carlo was constructed to simulate the elastic collisions with thermal partons by energetic jets.Medium modification due to jet-medium interaction has been studied within this model in a uniform medium.     

Two-particle angular correlations in pp and heavy-ion collisions

This paper presents a selected review of recent experimental results on two-particle angular correlations in AuAu and pp collisions. Two-particle correlations in AuAu collisions exhibit a rich structure as a function of hadron transverse momentum, carrying information about the expansion of the medium produced in nuclear collisions, the energy loss of high-p_T partons in the medium and the medium response to these high-p_T partons or other initial state inhomogeneities. Evidence on the interplay between initial state fluctuations and the final state correlation structure is discussed.