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Study of eta and omega meson mass shift in nuclei using recoil-less reactions

利用无反冲反应研究原子核中的 eta 和 omega 介子质量转移

基本信息

批准号：
11440073
负责人：
HAYANO Ryugo
金额：
$ 7.74万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2001
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-11440073/
关键词：
Quantum Chromo Dynamics pi meson eta meson omega meson effective mass GSI Cherenkov detector Chiral symmetry 中間子

项目摘要

Whether or not the masses of hadrons are modified in nuclear matter is one of the central problems of modern nuclear physics. In order to study this problem, there are many on-going efforts world wide to produce mesons in nuclei via high-energy heavy ion collisions, and to reconstruct the meson masses from the dilepton decays. The present study is based on an entirely different approach of "recoilless" production of mesons in nuclei, and of determination of their masses from the analyzes of Q-value spectra.We analyzed the deeply-bound pionic atom data (π^- meson bound in the 1s level of pionic ^<205>Pb atom), and unambiguously showed that the pi^- mass in lead nucleus is heavier by about 26 MeV as compared with its vacuum value. This result has been published in Physical Review Letters. In order to further study the contribution of the neutron/proton distribution difference on the meson mass, we performed another experiment using a series of Sn isotopes (different neutron numbers). The data are being analyzed, but preliminary results already show that the expected isotope effects are clearly seen.Our proposal to study eta (η) and omega (ω) meson mass shift in nuclei had already been approved at GSI laboratory in Darmstadt, Germany, but the beam time was deferred due to the fact that we chose to run the Sn experiment first. Meanwhile, we constructed a special focal-plane detector, sensitive to ^3He (our signal) but insensitive to protons (our background) based on the Cherenkov detection. The detector was tested at KEK, and was shown to perform as expected.

强子的质量是否在核物质中被修正是现代核物理的核心问题之一。为了研究这一问题，世界范围内正在进行许多努力，通过高能重离子碰撞在核中产生介子，并从双轻子衰变中重建介子质量。本研究基于一种完全不同的方法，即在原子核中“无反冲”产生介子，并通过Q值谱分析确定其质量。我们分析了深度束缚的π ^-介子数据（π^-介子束缚在π ^-Pb原子的1 s能级<205>上），并明确表明铅核中的π ^-质量比其真空值重约26 MeV。这一结果发表在《物理评论快报》上。为了进一步研究中子/质子分布差异对介子质量的贡献，我们使用一系列Sn同位素（不同中子数）进行了另一个实验。我们研究原子核中η介子和ω介子质量移动的建议已经在德国达姆施塔特的GSI实验室得到了批准，但是由于我们选择先进行Sn实验，束流时间被推迟了。与此同时，我们基于切伦科夫探测器，构造了一个特殊的焦平面探测器，它对^3He（我们的信号）敏感，但对质子（我们的背景）不敏感。该探测器在KEK进行了测试，结果显示其性能符合预期。