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Proton quasifree scattering at 1 GeV and medium effects in nuclear field

1 GeV 质子准自由散射和核场中的介质效应

基本信息

批准号：
15340080
负责人：
NORO Tetsuo
金额：
$ 8.9万
依托单位：
Kyushu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2005
项目状态：
已结题

项目摘要

This program was mainly performed as an international collaboration experiment held at Petersburg Nuclear Physics Institute in Russia by using the 1 GeV synchrocyclotron. Experiments at 400 MeV proton beam by using the cyclotron complex at Research Center for Nuclear Physics, Osaka University, and a collaboration work with Prof. Hillhouse, University of Schtellenbosch in South Africa, are also important parts of this program. Prof. Hillhouse stayed at Fukuoka for two to four months in 2004 and 2005, respectively. The purpose of this program was to investigate Dirac relativistic effects, which is one of possible nuclear medium effects in the hadronic level..The experiments in Russia were performed twice and the proton quasifree scattering off a 160 target, which is a p-shell nucleus, and a 40Ca target, an sd closed-shell nucleus. In the former case, only the differential cross section were measured for a reason in the preparation of detector system, while both of the cross section and induced polarization were measured in the latter case.It is a long staying problem that the analyzing power (Ay) for proton quasifree scattering is significantly reduced from the values estimated by using the nucleon-nucleon interaction in free space, but we firstly compare the reduction rate in a wide incident-energy region quantitatively. The result shows that the reduction rate is similar for both of 1 GeV and 400 MeV energies, from which we can conclude that the reduction is not caused by mixture of some complicated processes as two-step processes. From an experimental result with many kinds of target nuclei, it is also found that this reduction shows a monotone function of the Q-value of the reaction. From the theoretical side, it is found that only 50% of this reduction is explained as a Dirac relativistic effect. This may suggest existence of some additional medium effect, such as meson-mass modifications.

该计划主要是在俄罗斯彼得堡核物理研究所利用1 GeV同步回旋加速器进行的国际合作实验。利用大坂大学核物理研究中心的回旋加速器复合体进行的400 MeV质子束实验以及与南非Schtellenbosch大学Hillhouse教授的合作工作也是该计划的重要组成部分。Hillhouse教授在2004年和2005年分别在福冈停留了两到四个月。该计划的目的是研究Dirac相对论效应，这是强子水平上可能的核介质效应之一。在俄罗斯进行了两次实验，质子在160靶（p壳层核）和40 Ca靶（sd闭壳层核）上的准自由散射。在前一种情况下，由于探测器系统制备的原因，只测量了微分散射截面，而在后一种情况下，测量了散射截面和激发极化，这是一个长期存在的问题，即质子准自由散射的分析能力（Ay）明显低于自由空间中核子-核子相互作用的估计值，但我们首先定量地比较了宽入射能量范围内的减少率。结果表明，在1GeV和400 MeV能量范围内，两种能量下的还原速率基本相同，由此可以推断，这种还原不是由两步过程等复杂过程的混合引起的。从多种靶核的实验结果中还发现，这种减少是反应Q值的单调函数。从理论上讲，只有50%的这种减少被解释为狄拉克相对论效应。这可能表明存在一些额外的介质效应，如介子质量的修改。