LaTeX, 23 pages, 11 figures, extended version of contribution to the proceedings of the INT 10-3 program "Gluons and the quark sea at high energy: distribution, polarization, tomography", INT, Seattle, Sep.13-Nov.19, 2010
We discuss modeling of generalized parton distributions (GPDs), their access from present experiments, and the phenomenological potential of an electron-ion collider. In particular, we present a comparison of phenomenological models of GPD H, extracted from hard exclusive meson and photon production. Specific emphasis is given to the utilization of evolution effects at moderate x_Bj in a future high-luminosity experiment within a larger Q^2 lever arm.
The exclusive $π^0$ electroproduction is analyzed within the handbag approach based on Generalized Parton Distributions (GPDs) factorization. We consider the leading-twist contribution together with the transversity effects. It is shown that the transversity, $H_T$ and $\bar E_T$ GPDs are essential in the description of $π^0$ cross section. Predictions for future Electron-Ion Collider of China (EicC) energy range are done. It is found that transversity dominance $σ_T\ggσ_L$, observed at low energies is valid up to EicC energy range.
Exclusive $π^0$ electroproduction from nucleons at large $Q^2$ can be described by Generalized Parton Distributions (GPDs), particularly the chiral odd subset related to transversity. These GPDs can be accessed experimentally from various cross sections and asymmetries. We calculate these GPDs in a spectator model, constrained by boundary functions. Alternatively, in a hadronic picture the meson production amplitudes correspond to C-odd Regge exchanges with final state interactions. The helicity structure provides relations between the partonic and the hadronic, Regge description of C-odd, chi…
We demonstrate that the transversity chiral odd generalized parton distributions can be accessed through the azimuthal dependence of the nu N -> l D N' or nubar N -> l D N' differential cross sections, in the framework of the colinear QCD approach, where GPDs factorize from perturbatively calculable coefficient functions calculated up to order mc/Q.
Describing hadronic structure is one of the most intriguing problems in physics. In this respect, generalized parton distributions (GPDs) constitute an outstanding tool, allowing to draw "three dimensional pictures" of hadron's inside. Starting from contemporary models for pion's GPDs fulfilling all constraints imposed by QCD, we compute Compton form factors (CFFs) of pions subjected to deeply virtual Compton scattering. We show the behaviour of CFFs to be gluon-dominated at EIC's kinematics. Finally we evaluate lepton-beam-spin asymmetries in the Sullivan process, demonstrating the existence …
We discuss two collider processes which combine a diffractively produced $ρ$ meson separated by a large rapidity gap from a hard exclusive scattering of a Pomeron on a nucleon, giving rise to a lepton pair or to a second meson. These two processes probe the nucleon quark content described by generalized parton distributions in a very specific way.
We consider the exclusive photo-production of a photon-meson pair with a large invariant mass, working in the QCD factorisation framework. Explicitly, we consider a $ ρ$-meson or a charged $ π$ in the final state. This process gives access both to chiral-even GPDs and chiral-odd GPDs, which are not well-known experimentally, especially the latter ones. The computation is performed at leading order and leading twist. We discuss the prospects of measuring them in experiments, focusing on the kinematics at the JLab 12-GeV experiment, and pPb ultra-peripheral collisions at LHC. In particular, the …
We briefly report our recent progress on the study of the polarized fragmentation functions of $Λ$ hyperon in unpolarized semi-inclusive deep-inelastic scatterings and electron-positron annihilations at low energies. In particular, we present a simple but practical method on how to measure the azimuthal-angle-dependent longitudinal polarization and the transverse polarization inside the production plane and bridge these observables to the corresponding structure functions and fragmentation functions at the leading twist. Our work diversifies the high energy reactions that can probe the polariz…
Gluons inside unpolarized hadrons can be linearly polarized provided they have a nonzero transverse momentum. The simplest and theoretically safest way to probe this distribution of linearly polarized gluons is through cos(2 phi) asymmetries in heavy quark pair or dijet production in electron-hadron collisions. Future Electron-Ion Collider (EIC) or Large Hadron electron Collider (LHeC) experiments are ideally suited for this purpose. Here we estimate the maximum asymmetries for EIC kinematics.
Generalized parton distributions (GPDs) encoding multidimensional information of hadron partonic structure appear as the building blocks in a factorized description of hard exclusive reactions. The nucleon GPDs have been accessed by deeply virtual Compton scattering and deeply virtual meson production with lepton beam. A complementary probe with hadron beam is the exclusive pion-induced Drell-Yan process. We discuss recent theoretical advances on describing this process in terms of the partonic subprocess convoluted with the nucleon GPDs and the pion distribution amplitudes. Furthermore, we me…
Generalized parton distributions (GPDs) encoding multidimensional information of hadron partonic structure appear as the building blocks in a factorized description of hard exclusive reactions. The nucleon GPDs have been accessed by deeply virtual Compton scattering and deeply virtual meson production with lepton beam. A complementary probe with hadron beam is shown to be the exclusive pion-induced Drell-Yan process, $π^- p \to μ^+ μ^- n$, as demonstrated by recent theoretical advances on describing this process in terms of QCD factorization as the partonic subprocess convoluted with the nucle…
We study the exclusive photoproduction of a photon-meson pair with a large invariant mass, working in the QCD factorisation framework. Explicitly, we consider a $ ρ$-meson or a charged $ π$ in the final state. This process gives access to chiral-even GPDs as well as chiral-odd GPDs. We focus here on the chiral-even sector. The computation is performed at leading order and leading twist. We discuss the prospects of measuring them in various experiments such as JLab 12-GeV, COMPASS, future EIC and LHC (in ultraperipheral collisions). In particular, the high centre of mass energies available at c…
We report on the access of generalized parton distributions (GPDs) from deeply virtual Compton scattering (DVCS) measurements. We also point out that such measurements at a proposed high-luminosity electron-ion collider (EIC) provide insight in both the transverse distribution of sea quarks and gluons as well as the proton spin decomposition.
We calculate the $cos~2 ϕ$ asymmetry in $J/ψ$ production in electron-proton collision for the kinematics of the planned electron-ion collider (EIC). This directly probes the Weiszäcker-Williams (WW) type linearly polarized gluon distribution. Assuming generalized factorization, we calculate the asymmetry at next-to-leading-order (NLO) when the energy fraction of the $J/ψ$ satisfies $z<1$ and the dominating subprocess is $γ^* +g \rightarrow c + {\bar c}+g$. We use non-relativistic QCD based color singlet model for $J/ψ$ production. We investigate the small $x$ region which will be accessible at…
Generalized parton distributions (GPDs) encoding multidimensional information of hadron partonic structure appear as the building blocks in a factorized description of hard exclusive reactions. The nucleon GPDs have been accessed by deeply virtual Compton scattering and deeply virtual meson production with lepton beam. A complementary probe with hadron beam is the exclusive pion-induced Drell-Yan process. In this paper, we discuss recent theoretical advances on describing this process in terms of nucleon GPDs and pion distribution amplitudes. Furthermore, we address the feasibility of measurin…
This is a brief overview of the spin physics opportunities at a high energy, high luminosity, polarized Electron-Ion Collider (EIC). It covers measurements of electroweak polarized structure functions, quark and gluon PDFs, TMDs, GPDs and GTMDs. Exploiting the many possible final states allows to probe various spin effects. Open and bound heavy quark production can be used to probe gluon TMDs, but also color-octet NRQCD long distance matrix elements. Spin-dependent fragmentation functions can be used too, but are also interesting in themselves. Especially for studies of the small-$x$ and the h…
In this work, we present a systematic study on the feasibility of probing the largely unexplored transverse momentum dependent gluon Sivers function (GSF) in open charm production, high p$_T$ charged di-hadron and di-jet production at a future high energy, high luminosity Electron-Ion Collider (EIC). The Sivers function is a measure for the anisotropy of the parton distributions in momentum space inside a transversely polarized nucleon. It is proposed that it can be studied through single spin asymmetries in the photon-gluon fusion subprocess in electron proton collisions at the EIC. Using a w…
The quark orbital angular momentum (OAM) has been recognized as an important piece of the proton spin puzzle. A lot of effort has been invested in trying to extract it quantitatively from the generalized parton distributions (GPDs) and the transverse-momentum dependent parton distributions (TMDs), which are accessed in high-energy processes and provide three-dimensional pictures of the nucleon. Recently, we have shown that it is more natural to access the quark OAM from the phase-space or Wigner distributions. We discuss the concept of Wigner distributions in the context of quantum field theor…
We review the phenomenological framework for accessing Generalized Parton Distributions (GPDs) using measurements of Deeply Virtual Compton Scattering (DVCS) from a proton target. We describe various GPD models and fitting procedures, emphasizing specific challenges posed both by the internal structure and properties of the GPD functions and by their relation to observables. Bearing in mind forthcoming data of unprecedented accuracy, we give a set of recommendations to better define the pathway for a precise extraction of GPDs from experiment.
Dynamical gluon effects in twist-3 generalized parton distributions of the proton
Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；School of Nuclear Science and Technology, University of Chinese Academy of Sciences（中国科学院大学核科学与技术学院）
We present a full evaluation of the deeply virtual Compton scattering (DVCS) cross section in the dipole framework in the small-x region. The result features the $\cos ϕ$ and $\cos 2ϕ$ azimuthal angular correlations which have been missing in previous studies based on the dipole model. In particular, the $\cos 2ϕ$ term is generated by the elliptic gluon Wigner distribution whose measurement at the planned electron-ion collider (EIC) provides an important information about the gluon tomography at small-x. We also show the consistency with the standard collinear factorization approach based on t…
Accessing chiral-even quark generalised parton distributions in the exclusive photoproduction of a $ γπ^{\pm} $ pair with large invariant mass in both fixed-target and collider experiments
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 on nuclear shadowing at small $x_{bj}$ and the interplay of …
The field of Generalized Parton Distribution (GPD) benefited from a wealth of exclusive reactions measurements since 2000. Extraction of GPDs from observables has begun with this first generation of experiments. In the short and mid-term future the programs of COMPASS-II and JLab at 12 GeV will enlarge the existing kinematic domain and open an era of high-precision measurements. Tools for phenomenological analysis are being developed at the same time and will be mature to handle these forthcoming measurements. In the long-term future the EIC project will allow an ambitious spin program in the …
Three-dimensional imaging of hadrons with hard exclusive reactions: advances in experiment, theory, phenomenology, and lattice QCD
NRC “Kurchatov Institute” - PNPI（库尔恰托夫国家研究中心 - 彼得堡核物理研究所）；INFN Laboratori Nazionali di Frascati（意大利国家核物理研究所弗拉斯卡蒂实验室）；Virginia Tech（弗吉尼亚理工大学）；Thomas Jefferson National Accelerator Facility（托马斯·杰斐逊国家加速器设施）；Temple University（天普大学）；Department of Physics, Kyungpook National University（庆北国立大学物理系）；BenGurion（本古里安大学）；IRB（意大利国家核物理研究所）；INFN（意大利国家核物理研究所）
Deeply virtual pion production through two-loop order
State Key Laboratory of Nuclear Physics and Technology, Institute of Quantum Matter, South China Normal University（华南师范大学量子物质研究所核物理与技术国家重点实验室）；Guangdong Basic Research Center of Excellence for Structure and Fundamental Interactions of Matter, Guangdong Provincial Key Laboratory of Nuclear Science（广东省基础与应用基础研究基地物质结构与基本相互作用卓越中心广东省核科学重点实验室）；China University of Mining and Technology（中国矿业大学）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；School of Physics, Zhengzhou University（郑州大学物理学院）；School of Physical Sciences, University of Chinese Academy of Sciences（中国科学院大学物理科学学院）
本文首次计算了在广义BJorken极限下，γ_L* p→π+ n和γ_L* p→π^0 p过程的次次leading order (NNLO) QCD辐射修正，这些修正显著提高了perturbative QCD预测与JLab数据的一致性，并研究了双环QCD修正对纵向DVπP横截面及某些基准动量下横单旋不对称性(TSSA)的影响。
We extend our studies of a new class of $2 \to 3$ exclusive processes using the collinear factorisation framework by considering the exclusive photoproduction of a $γ\,ρ$ pair, in the kinematics where the pair has a large invariant mass, {and the outgoing $ ρ$-meson has a sufficiently large transverse momentum to not resonate with the nucleon}. We cover the whole kinematical range from medium energies in fixed target experiments to very large energies of colliders, by considering the experimental conditions of JLab~12-GeV, COMPASS, future EIC and LHC (in ultra-peripheral collisions) cases. One…
We present a summary of a recent workshop held at Duke University on Partonic Transverse Momentum in Hadrons: Quark Spin-Orbit Correlations and Quark-Gluon Interactions. The transverse momentum dependent parton distribution functions (TMDs), parton-to-hadron fragmentation functions, and multi-parton correlation functions, were discussed extensively at the Duke workshop. In this paper, we summarize first the theoretical issues concerning the study of partonic structure of hadrons at a future electron-ion collider (EIC) with emphasis on the TMDs. We then present simulation results on experimenta…
Exclusive vector-quarkonium photoproduction at NLO in alpha_s in collinear factorisation with evolution of the generalised parton distributions and high-energy resummation
