Study of relativistic effects in nuclear physics

通过东北大学、马萨诸塞州理工学院和美国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流（MEC）在核反应中的贡献<16><40>。这些结果和<12>以前得到的关于^ C的结果与意大利Pavia小组的理论计算进行了比较。计算高估了实验截面的一个因素的两个所有三个核。这表明在理论计算中遗漏了一些重要的成分。研究结果已在JPS会议和在法国格勒诺布尔举行的讲习班上介绍，并发表在LNS的研究报告中。在<12>MIT-Bates测量的质子电产生中性π介子的实验数据已作为两篇论文发表。测量了四极光子吸收多极子，并讨论了核子的形变。所测得的四极振幅远大于夸克模型的预测值。它被解释为验证了π介子云的关键作用。结果发现，真实的和虚部的横向横截面是在合理的协议，只有美因茨大学的酉模型（MAID）。然而，该模型完全是经验性的，并且已知其他一些实验存在问题。3.在杰斐逊实验室完成的^3He的（e，e 'p）pn反应实验已经发表。结果表明，即使对于轻核^3He，末态相互作用也是重要的。三体破碎通道的破裂速度比两体破碎通道的破裂速度大，特别是在高动量损失时。

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.