Study of relativistic effects in nuclear physics

通过东北大学、麻省理工学院和托马斯-杰斐逊国家实验室的电子散射实验，研究了相对论效应和介子交换电流（MEC）在核反应中的贡献。（e,e’p）实验在东北大学的^<16>O和^<40>Ca上进行。这些结果和先前得到的^<12>C的结果，与意大利Pavia小组的理论计算结果进行了比较。计算对所有三个核的实验截面都高估了两倍。这表明理论计算中缺少一些重要的成分。研究结果已在法国格勒诺布尔举行的JPS会议和研讨会上发表，并发表在LNS的研究报告中。^< 12b> C实验的论文全文已提交给Physical Review C.2。在麻省理工学院贝茨分校测量的质子电产生中性介子的实验数据已作为两篇论文发表。测量了四极子光子吸收多极子，并从数据上讨论了核子的变形，得到的四极子振幅比夸克模型预测的值大得多。它被解释为对介子云的关键作用的验证。发现纵横截面的实部和虚部仅与美因茨大学统一模型（MAID）有合理的一致性。然而，该模型完全是经验的，并且已知其他一些实验存在问题。要全面了解核子的结构，还需要进行更多的研究。在杰斐逊实验室进行的^3He上的（e,e'p）pn反应实验已经发表。结果表明，即使在^3He轻核上，末态相互作用也是重要的。三体破碎通道比二体破碎通道更大，特别是在高丢失动量时。

Contributions of relativistic effects and meson exchange currents (MEC) in the nuclear reaction have been investigated through electron scattering experiments at Tohoku University, Massachusetts Institute of Technology, and Thomas-Jefferson National Laboratory.1.The (e,e'p) experiments have been performed on ^<16>O and ^<40>Ca at Tohoku University. Those results and the result on ^<12>C, which had been previously obtained, were compared with theoretical calculations made by Pavia group in Italy. The calculation overestimates the experimental cross section by a factor of two for all three nuclei. It indicates that some important ingredients are missing in the theoretical calculation. The results have been presented in JPS meetings and a workshop held at Grenoble in France, in addition to publication in Research Report of LNS. The full paper of ^<12>C experiment has been submitted to Physical Review C.2.Experimental data of electro-production of neutral pion from the proton measured at MIT -Bates have been published as two papers. Quadrupole photon absorption multipoles were measured, and the deformation of the nucleon has been discussed from the data The obtained quadrupole amplitudes are much larger than the values predicted by quark models. It is interpreted as a validation of the crucial role the pion cloud. It is found that real and imaginary parts of the longitudinal-transverse cross section are in reasonable agreement with only the Mainz University Unitary model (MAID). However, the model is entirely empirical and is known there are problems with some other experiments. More investigation is needed to reach the entire understanding of the nucleon structure.3.The experiment of the (e,e'p)pn reaction on ^3He performed at the Jefferson Lab has been published. The result shows the final state interaction is important even on light nuclei as ^3He. It is larger for three-body breakup channel than for two-body breakup channel, especially at high missing momenta.