Study of relativistic effects in nuclear physics

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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.