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

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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.