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Studies of Spin Structure of Proton and Neutron by HERMES - High Precision Hadron Indentification with a Ring Imaging Cherenkov Detector

HERMES 研究质子和中子的自旋结构 - 使用环形成像切伦科夫探测器进行高精度强子识别

基本信息

批准号：
13440073
负责人：
SHIBATA Toshi-aki
金额：
$ 9.15万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2003
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-13440073/
关键词：
Spin Proton neutron quark electron scattering elementary particle structure function gluon

项目摘要

The purpose of this research is to study how spin 1/2 of proton and neutron are composed from quarks and gluons. It was discovered 17 years ago that the quark spin contribution to the proton spin is small. This is called 'Nucleon Spin Problem'. We investigated this problem with a novel experimental technique.The experiment was called HERMES and was carried out at DESY in Germany. It is a deep inelastic scattering experiment with 27.5 GeV electron beam and polarized proton and deuteron target. Data accumulated by HERMES were sent to Tokyo Tech where we have a facility of data analyses. Our new technique is Ring Imaging Cherenkov Detector with which we can identify hadrons which are detected in coincidence with the scattered electon.As the first achievement, we can cite the quark flavor decomposition of helicity distribution Δu, Δd, Δs et al. The experimental results clearly show that u quark is polarized parallel to the proton spin, while d quark is polarized in opposite direction. The polarization of sea quarks are almost zero.As the second achievement, spin asymmetry due to deeply virtual Compton scattering was observed for the first time. This was useful data as input to the study of Generalized Parton Distributions'.As the third achievement, using a transversely polarized proton target, we succeeded in extracting Sivers effect and Collins effect separately. This has opened up a new field in the hadron spin physics.

本研究的目的是研究自旋为1/2的质子和中子如何由夸克和胶子组成。17年前，人们发现夸克自旋对质子自旋的贡献很小。这就是所谓的“核子自旋问题”。我们用一种新的实验技术研究了这个问题，这个实验被称为爱马仕，在德国的DESY进行。这是一个27.5GeV电子束与极化质子和氘靶的深度非弹性散射实验。爱马仕积累的数据被发送到东京工业大学，我们在那里有一个数据分析设施。我们的新技术是环形成像切伦科夫探测器，利用它可以识别出与散射电子相符合的强子.作为第一个成果，我们可以引用螺旋度分布的夸克味分解Δu，Δd，Δs等.实验结果清楚地表明，u夸克的极化方向平行于质子自旋，而d夸克的极化方向相反.作为第二项成果，我们首次观测到了由深虚康普顿散射引起的自旋不对称性。作为第三项成果，我们利用横向极化质子靶成功地分别提取了Sivers效应和柯林斯效应。这为强子自旋物理开辟了一个新的领域。