Measurement of deeply virtual Compton scattering off Helium-4 with CLAS at Jefferson Lab
R. Dupré, M. Hattawy, N. A. Baltzell, S. Bültmann, R. De Vita, A. El Alaoui, L. El Fassi, H. Egiyan, F. X. Girod, M. Guidal, K. Hafidi, D. Jenkins, S. Liuti, Y.… 展开作者
R. Dupré, M. Hattawy, N. A. Baltzell, S. Bültmann, R. De Vita, A. El Alaoui, L. El Fassi, H. Egiyan, F. X. Girod, M. Guidal, K. Hafidi, D. Jenkins, S. Liuti, Y. Perrin, S. Stepanyan, B. Torayev, E. Voutier, M. J. Amaryan, W. R. Armstrong, H. Atac, C. Ayerbe Gayoso, L. Barion, M. Battaglieri, I. Bedlinskiy, F. Benmokhtar, A. Bianconi, A. S. Biselli, M. Bondi, F. Bossù, S. Boiarinov, W. J. Briscoe, D. Bulumulla, V. Burkert, D. S. Carman, J. C. Carvajal, M. Caudron, A. Celentano, P. Chatagnon, V. Chesnokov, T. Chetry, G. Ciullo, B. A. Clary, P. L. Cole, M. Contalbrigo, G. Costantini, V. Crede, A. D'Angelo, N. Dashyan, M. Defurne, A. Deur, S. Diehl, C. Djalali, M. Ehrhart, L. Elouadrhiri, P. Eugenio, S. Fegan, A. Filippi, T. A. Forest, Y. Ghandilyan, G. P. Gilfoyle, R. W. Gothe, K. A. Griffioen, H. Hakobyan, T. B. Hayward, K. Hicks, A. Hobart, M. Holtrop, Y. Ilieva, D. G. Ireland, E. L. Isupov, H. S. Jo, K. Joo, S. Joosten, D. Keller, G. Khachatryan, A. Khanal, M. Khandaker, A. Kim, W. Kim, A. Kripko, V. Kubarovsky, S. E. Kuhn, L. Lanza, K. Livingston, M. L. Kabir, M. Leali, P. Lenisa, I. J. D. MacGregor, D. Marchand, N. Markov, V. Mascagna, M. Mayer, B. McKinnon, M. Mirazita, V. I. Mokeev, K. Neupane, S. Niccolai, T. R. O'Connell, M. Osipenko, M. Paolone, L. L. Pappalardo, R. Paremuzyan, E. Pasyuk, D. Payette, W. Phelps, N. Pivnyuk, O. Pogorelko, J. Poudel, Y. Prok, M. Ripani, J. Ritman, A. Rizzo, G. Rosner, P. Rossi, J. Rowley, F. Sabatié, C. Salgado, A. Schmidt, R. Schumacher, V. Sergeyeva, Y. Sharabian, U. Shrestha, D. Sokhan, O. Soto, N. Sparveris, I. I. Strakovsky, S. Strauch, N. Tyler, M. Ungaro, L. Venturelli, H. Voskanyan, A. Vossen, D. Watts, K. Wei, X. Wei, L. B. Weinstein, R. Wishart, M. H. Wood, B. Yale, N. Zachariou, J. Zhang
本文报道用Jefferson实验室的CEBAF大接收谱仪（CLAS）测量了$^4$ He的深虚康普顿散射中的束流自旋不对称性。该谱仪使用6 GeV的纵向极化电子束入射到加压的$^4$ He气体靶上。我们详细介绍了用于确保所测量的反应的排他性的方法，特别是升级CLAS与径向时间投影室检测低能量反冲$^4$ He核和内部量热计，以延长光子探测接受在前进的角度。我们的研究结果证实了理论预测的增强相干（$e^4$他$~\to~e'$ $^4$他$'γ'$）束的自旋不对称性上观察到的自由质子相比，而非相干（$e^4$他$~\to~e'$ p $'γ'$ X $'$）不对称性表现出30 $\%$抑制。从相干数据中，我们能够提取，在一个模型独立的方式，实部和虚部的唯一的$^4$他康普顿形状因子，$\cal H_A$，领导的方式向3D成像的部分结构的核。
英文摘要：
We report on the measurement of the beam spin asymmetry in the deeply virtual Compton scattering off $^4$He using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab using a 6 GeV longitudinally polarized electron beam incident on a pressurized $^4$He gaseous target. We detail the method used to ensure the exclusivity of the measured reactions, in particular the upgrade of CLAS with a radial time projection chamber to detect the low-energy recoiling $^4$He nuclei and an inner calorimeter to extend the photon detection acceptance at forward angles. Our results confirm the theoretically predicted enhancement of the coherent ($e^4$He$~\to~e'$$^4$He$'γ'$) beam spin asymmetries compared to those observed on the free proton, while the incoherent ($e^4$He$~\to~e'$p$'γ'$X$'$) asymmetries exhibit a 30$\%$ suppression. From the coherent data, we were able to extract, in a model-independent way, the real and imaginary parts of the only $^4$He Compton form factor, $\cal H_A$, leading the way toward 3D imaging of the partonic structure of nuclei.
Deeply virtual Compton scattering at Jefferson Laboratory
广义部分子分布（GPD）已经成为描述强子的基本成分夸克和胶子的通用工具。质子或中子（$N$）上的深度虚康普顿散射（DVCS），$e N \rightarrow e' N' γ$，是根据GPD更直接可解释的过程。DVCS和Bethe-Heitler的振幅，即入射或散射电子发射光子的过程，可以通过横截面测量或利用它们的干涉来获得，这会引起自旋不对称。自旋不对称性、横截面和横截面差异可以与每种夸克味的四种领先扭转GPD（${H}$、${E}$、${\tilde{H}}$、${\tilde{E}}$）的不同组合联系起来，这取决于可观察的目标和目标的类型。本文概述了杰斐逊实验室在A厅和B厅进行的DVCS的最新实验结果。几个实验已经完成了提取DVCS观测大的运动学区域。具有重叠运动学区域的多个测量允许执行康普顿形状因子的准模型独立提取，康普顿形状因子是GPD积分，揭示核子的3D图像。
Rosenbluth separation of $ \boldsymbol {dσ_{L}/dt}$ and $\boldsymbol {dσ_{T}/dt}$ in $\boldsymbol π^{\bf 0}$ deeply virtual electroproduction from the proton
