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Modification of the nucleon-nucleon scattering amplitude by nuclear medium effects

核介质效应对核子-核子散射幅度的修改

基本信息

批准号：
07640401
负责人：
NORO Tetsuo
金额：
$ 1.22万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-07640401/
关键词：
quasifree scattering medium effect nucleon-nucleon scattering amplitude Dirac approach effective mass analyzing power 偏極移行

项目摘要

Nuclear medium effect has been investigated experimentally through nucleon quasifree scattering. Exclusive measurements of the quasifree scattering give a direct way to study the nucleon-nucleon interaction in nuclear medium and is is expected to extract information on the properties of nucleons and mesons in nuclear field. For this puroose, defferential cross sections and analyzing powers (Ay) have been measured for the proton knockout reaction from s_<1/2> orbits of several target nuclei by using the ring cyclotron at Research Center for Nuclear Physics, Osaka University. The Ay values are reduce from those of free proton-proton scattering and the reduction rate is found to depend on target. We found that an averaged density seen through this reaction can be estimated in a special case where the recoil momentum, which corresponds to the experimental setting employed in this study, is zero and it reaches almost half of the nuclear saturation density in some cases. The reduction of Ay shows a monotomically decreasing function of the averaged density, which strongly suggests the existence of a nuclear medium effect on the nucleon-nucleon interaction. This result has been compared with the prediction by the Dirac approach. In this approach, , modification of the nucleon spinor in nuclear field is described as a reduction of the effective nucleon mass. We estimate the effective nucleon mass by using the averaged density defined above and calculate the modefication of the nucleon-nucleon observables by following the procedure proposed by a theoretical group in Indiana university. The calculation gives a qualitatively consistent result with our experimental result.

用核子准自由散射实验研究了核介质效应。准自由散射的独家测量为研究核介质中核子-核子相互作用提供了一种直接的途径，有望从核场中提取有关核子和介子性质的信息。为此，我们用大坂大学核物理研究中心的环形回旋加速器测量了几个靶核s_<1/2>轨道质子敲除反应的不同截面和分析本领（Ay）。Ay值从自由质子-质子散射的Ay值减小，并且减小速率依赖于靶。我们发现，通过这个反应看到的平均密度可以估计在一个特殊的情况下，反冲动量，这对应于在这项研究中采用的实验设置，是零，它几乎达到一半的核饱和密度在某些情况下。Ay的减少表明平均密度的单调递减函数，这强烈地表明存在核介质对核子-核子相互作用的影响。这一结果已与狄拉克方法的预测。在这种方法中，核子旋量在核场中的改变被描述为核子有效质量的减少。我们利用上述定义的平均密度估计了核子的有效质量，并按照印第安纳州大学的一个理论小组提出的方法计算了核子-核子观测量的模化。计算结果与实验结果定性一致。