Study of Spin Structure of the Nucleon with Hadron Coincidence Method

在这个援外项目中，我们利用实验技术研究了质子和中子的自旋是如何由夸克和胶子组成的，其自旋是1/2。它是一种强相互作用理论——量子色动力学的研究。我们在德国DESY参加了HERMES实验。高能极化电子束从极化的靶核子上散射出去。在最终态（介子、核子、λ等）中，同时也发现了散射的电子和产生的强子。这些数据被发送到世界各地的合作大学和研究所。东京工业大学的数据分析设备在数据分析中发挥了重要作用。研究结果发表在期刊上。在这个项目中，一个环形成像切伦科夫计数器（RICH）被开发并安装到HERMES实验中。介子、介子、质子和反质子现在被认定为RICH。可以研究核子中极化的u、d、s夸克。它们的动量分布已经确定。到目前为止，在几个GeV/c以上的粒子-介子分离一直很困难，但HERMES用RICH解决了这个问题。这一技术突破的影响很大。作为物理学的成果，最大的成就是研究了横向极化的夸克分布。我们通过观察方位角认识到这一点，方位角是电子散射面和介子产生方向之间的角度。测量了方位角分布对目标自旋方向的依赖性。用这种方法研究了自旋与舅舅子自旋垂直的夸克的分布。这将成为一个新的研究领域，吸引大量物理学家对这一课题进行进一步的研究。

In this project of Grand-in-Aid we have studied how the spin of proton and neutron, which is 1/2, is composed of quarks and gluons with use of experimental techniques. It is a research of Quantumchromodynamics which is a theory of strong interaction.We participated in HERMES experiment at DESY in Germany. The high energy polarized electron beam is scattered off the polarized target nucleon. The scattered electron as well as produced hadrons in the final state (mesons, nucleons, lambdas etc.) were detected in coincidence. The data were sent to the collaborating universities and institutes worldwide. The data-analysis equipment at Tokyo Institute of Technology played an important role in the data-analysis. The results were published in journals.During this project a Ring Imaging CHerenkov Counter (RICH) was developped and installed into HERMES experiment. Pions, kaons, protons and anti-protons are now identified with the RICH.Polarized u, d, and s quarks in the nucleon can be studied. Their momentum distributions have been determined. Pion-kaon separation had been difficult above several GeV/c up to now but HERMES solved it with the RICH.This technical breakthrough has a large impact.As an outcome of phycics, the largest achievement is that the transversely polarized quark distribution was studied. We realized this by looking at the azimuthal angle which is the angle between the electron scattering plane and the pion production direction. The dependence on the target spin direction of the azimuthal angle distribution was measured. This way the distribution of the quark which has the spin perpendicular to the uncleon spin is studied. This will become a new field of research and attract a large number of physicists to further investigate this subject.