Understanding various fundamental properties of nucleons and nuclei are among the most important scientific goals at the upcoming Electron-Ion Collider (EIC). With the unprecedented opportunity provided by the next-generation machine, the EIC might provide definitive answers to many standing puzzles and open questions in modern nuclear physics. Here we investigate one of the golden measurements proposed at the EIC, which is to obtain the spatial gluon density distribution within a lead ($Pb$) nucleus. The proposed experimental process is the exclusive $J/ψ$ vector-meson production off the $Pb$ nucleus - $e+Pb\rightarrow e'+J/ψ+Pb'$. The Fourier transformation of the momentum transfer $|t|$ distribution of the coherent diffraction is the transverse gluon spatial distribution. In order to measure it, the experiment has to overcome an overwhelmingly large background arising from the incoherent diffractive production, where the nucleus $Pb'$ mostly breaks up into fragments of particles in the far-forward direction close to the hadron-going beam rapidity. In this paper, we systematically study the rejection of incoherent $J/ψ$ production by vetoing products from these nuclear breakups - protons, neutrons, and photons, which is based on the BeAGLE event generator and the most up-to-date EIC Far-forward Interaction Region design. The achieved vetoing efficiency, the ratio between the number of vetoed events and total incoherent events, ranges from about 80% - 99% depending on $|t|$, which can resolve at least the first minimum of the coherent diffractive distribution based on the Sar$\it{t}$re model. Experimental and accelerator machine challenges as well as potential improvements are discussed.
Institute for Nuclear Theory, University of Washington（华盛顿大学核理论研究所）；Northwestern University（西北大学）；KEK Theory Center, IPNS, KEK（高能加速器研究机构理论中心）；Theoretical Division, Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室理论部）
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。
Separating coherent and incoherent photoproduction at an Electron-Ion Collider: Comparing lead, gold and silver beams
Nuclear Science Division, Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室核科学部）；Department of Physics and Astronomy, University of California, Davis（加州大学戴维斯分校物理与天文学系）
