Study of Spin Structure of the Proton and Nectron with Hadror Coincidence Method

在本项目中，我们在东京工业大学进行了1)实验数据分析和2)探测器研制。该项目的主题是研究质子和中子自旋的夸克-胶子结构。核子的自旋是1/2。1988年，EMC发现只有一小部分核子自旋是由夸克携带的。我们正在德国汉堡的DESY参加爱马仕实验。在爱马仕，高能极化电子束从极化的核子靶上散射出来。实验数据是从爱马仕送到我们大学的。这个实验是深度非弹性散射。我们不仅测量了散射电子，而且还测量了产生的强子(介子、核子、波长等)。纯属巧合。为此，我们研制了环形成像切伦科夫计数器(RICH)，并将其安装在HERMES中。用RICH对2-20Gev/c的正子、介子、质子和反质子进行了识别，确定了极化u、d和S夸克在核子中的分布。此外，还首次研究了夸克自旋的横截面。这是对自旋垂直于核子自旋的夸克分布的研究。在Hermes上，通过反转目标核子的自旋方向，测量了电子散射面与介子产生方向之间的夹角。我们成功地观察到了一个非零的不对称性。夸克自旋的横向度是一个新的领域，在不久的将来将吸引许多物理学家对其进行进一步的研究。

In this project we have done 1) the experimental data analysis and 2) detector development at Tokyo Institute of Technology. The thema oa the project was the study of the quark-gluon structure of the spin of proton and neutron. The spin of the nucleon is 1/2. It was found by EMC in 1988 that only a small part of the nucleon spin is carried by quarks. We are participating in HERMES experiment at DESY in Hamburg in Germany. At HERMES the high energy polarized electron beam is scattered off the polarized nucleon target. The experimental data are sent from HERMES to our university. This experiment is a deep inelastic scattering. We mea sured not only the scattered electron but also produced hadrons (mesons, nucleons, lambda etc.) in coincidence. For that purpose we developped a Ring Imag ing CHerenkov counter (RICH) and installed into HERMES.Pions, kaons, protons and anti-protons at 2-20Gev/c are identified with the RICH.Polarized u, d, and s quark distributions in the nucleon are determined.Furthremore, transversity of the quark spin was studied for the first time. This is a study of the distribution of the quark whose spin is perpendicular to the nucleon spin. At HERMES the angle between the electron scattering plane and the pion production direction was measured by reversing the target nucleon spin direction. We succeeded to observe a non-zero asymmetry. 'Transversity' of the quark spin is a new field and will attract many physicists in the near future to study it further.