Study of spin structure of the proton and the neutron with new experimental technique at HERMES

大约20年前，欧洲核子研究中心的EMC发现，夸克自旋对质子自旋的贡献很小。它被称为‘质子自旋问题’。爱马仕实验是来自11个国家的国际合作，以独特的技术能力研究这个问题。使用27.6GeV的DESY-HERA电子或正电子束和内部气体靶，测量了电子与核子的深度非弹性散射。爱马仕探测到散射的电子，也产生强子。在强子识别方面，RICH(环形成像切伦科夫探测器)发挥了主要作用，Herme于1995年开始数据采集，2007年7月完成数据采集。我们已经连续10年得到助学金的支持，这是最近两年。在这两年中，我们发表了对质子、中子和氚的G1(X)结构函数的精确测量结果。与非极化深度非弹性散射中的F2(X)结构函数一样，G1(X)是基本结构函数。我们用这个G1(X)精确地确定了夸克自旋对核子自旋的贡献。我们还发表了用深度非弹性散射研究强子化的结果。换句话说，强子化就是碎片化。为此，我们测量了多重数，即强子每次深度非弹性散射的产额。在深度非弹性散射中测定的碎裂函数可以与电子-正电子对撞机实验得到的碎裂函数相比较。我们发表了产生的Lambda粒子的纵向和横向极化。最后，我们对DGLAP演化方程进行了微扰QCD的理论计算，并对世界数据进行了一致性分析。

It was found about 20 years ago by EMC at CERN that the quark spin contribution to the proton spin is small. It is called 'proton spin problem'. The HERMES experiment is an international collaboration from 11 countries to study this problem with unique technical capabilities. Electron or positron beam of DESY-HERA of 27.6 GeV and internal gas targets are used Deep-inelastic scattering of electron off the nucleon is measured. The HERMES detects the scattered electron and also produced hadrons. For the hadron identification, the RICH(ring imaging Cherenkov detector) plays a main role.The HERME started its data-taking in 1995 and the data-taking was completed in July 2007. We have received support by Grant-in-aid continuously for 10 years and this was the last two years. During these two years, we published the result of precision measurement of g1(x) structure functions for proton, neutron and deuteron. Like F2(x) structure function in the unpolarized deep inelastic scattering, g1(x) is the fundamental structure function. We determined the quark spin contribution to the nucleon spin with a good precision using this g1(x).We also published the results of hadronization studied by deep-inelastic scattering. Hadronization is in other words fragmentation. For this we measured the multiplicity which is hadron yield per deep inelastic scattering. The fragmentation function determined in deep inelastic scattering can be compared to the one from electron-positron collider experiments.We published the longitudinal and transverse polarization of produced Lambda particles. It is important to extend the study of baryon spin in a way to include strange quark.Finally, we did theoretical calculation of perturbative QCD for DGLAP evolution equation and analyzed the world data in a consistent way.