The measurement of the spin-dependent structure function g_2 (x, Q^2) and test of QCD higher twist effect

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The study of the nucleon spin structure aims to make clear the role of quarks inside nucleon and to verify the QCD which predicts the quark-gluon behavior. We made the research work to investigate the quark spin content to the nucleon spin and test the QCD sum rule performing the deep-inelastic scattering of polarized muon of polarized proton and deuteron. Morever, we developed the spin polarized target which is the most essential tool for the experiment. We will show the resuts dividing into two items.(1) The development of the spin polarized target(a) The establishment of the spin rotation method : In order to test the higher twist effect in the deep-inelastic scattering, one has to polarize the target spin perpendicular to the muon spin which has a parallel direction to its momentum. For that, one has to rotate the spin 90 degree by a dipole magnet from beam axis. We measured the depolarization by this rotation and found it looses 1% per 1 rotation. We established this method and pe … More rformed the measurement of A_2 asymmetry successfully.(b) For the better determination of the polarization, we renewed the NMR system and developed the new material polyethylene which has several merits as target material. We tested polyethylene foil and got the polarization of -66% and +40%. The value of the polarization is still the maximum in the world for the polyethylene foil at present.(2) The determination of the nucleon spin structure(a) We summarized the data taken in 1994 for the proton. the results showed fairly improved statistics and extension of the measured x region to the lower side. As a result, it has been made clear that the 1st moment G^p_ derived from Ellis-Jaffe sum rule has 2 standard deviation from the experiment. Followingly, the quark spin has only (20-30)% conribution to the nucleon spin.(b) In 1993, the parameter g_2 (x) for the proton has been also measured. The data is not enough to discuss on detail about the 3rd twist derived from this parameter, but 4 data points are consistent with no effect of the 3rd twist to g_2 (x). Moreovere, the data was quite usuful for the suppression of the systematic error brought into g_1 (x) from the neglect of this value.(c) In 1994 and 1995, the g_1 (x) for the deuteron has been measured. The data taken in 1995 is now being analyzed, The data in 1994 has been already analyzed and gave a good statistics mixing with the data in 1992. The Bjorken sum rule has been tested by the nuetron g_1 (x) derived from the deuteron data and proton one and showed the agreement within 10%. Less