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Life-time measurement of the para-positronium

对正电子素的寿命测量

基本信息

批准号：
08404016
负责人：
ENDO Ichita
金额：
$ 26.11万
依托单位：
Hiroshima University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1999
项目状态：
已结题

项目摘要

The positronium Ps is a bound state of an electron and a positron and is a good test ground of the quantum electro dynamics. The life time of the spin-0 Ps, the para-positronium (p-Ps), has never been measured directly upto date. This is because the life time of p-Ps is very short, about 0.1 ns and is not accessible with conventional measuring method. In this research we propose to measure it based on a completely new idea; use of high-energy positronium beam. The main points are as follows.(a) The life time is longer when the Ps has higher kinetic energy.(b) Theoretical prediction exists that a high energy monochromatic Ps can be produced from a crystal-target.(c) Detection of high energy Ps with the field-ionization method is possible in the magnetic field is possible owing to the relativistic effect.For realizing an life-time measuring system based on the above items, we carried out preliminary experiments and construction works. The finding and achievement so far made are summarized as follows.(a) In an experiment using a 350MeV photon beam, we found a significant enhancement of pair-production cross section on a single crystal at a predicted photon energy.(b) The amount of enhancement is found to be the larger and the narrower when the emission angle is restricted to the smaller angular cone, thus supporting the theoretical prediction of Ps production from a crystal.(c) The experimental apparatus for coherent production of positronia and their detection has bee constructed and set up at the 150MeV electron facility REFER in Hiroshima University to be used in the long beam time to come.

正电子素Ps是一个电子和一个正电子的束缚态，是量子电动力学的一个很好的实验场。自旋为0的Ps的寿命，也就是对位电子偶素（p-Ps）的寿命，至今还没有被直接测量过。这是因为p-Ps的寿命非常短，约为0.1 ns，并且无法用常规测量方法测量。在这项研究中，我们提出了一个全新的想法来测量它;使用高能正电子素束。主要观点如下。(a)当Ps具有较高的动能时，寿命较长。(b)理论预测存在的高能量单色Ps可以产生从晶体靶。(c)由于相对论效应，在磁场中用场电离方法探测高能Ps是可能的。为了实现基于上述项目的寿命测量系统，我们进行了初步的实验和构建工作。现将研究结果和取得的成果总结如下。(a)在使用350 MeV光子束的实验中，我们发现在预测的光子能量下，单晶上的成对产生截面显著增强。(b)发现当发射角限制在较小的锥角时，增强量越大，增强量越窄，从而支持从晶体生产Ps的理论预测。(c)在广岛大学150 MeV电子装置REFER上建造了正电子子相干产生和探测的实验装置，以用于未来的长束流时代。