Test of non-perturbative QCD by means of the measurement of Kπ scattering length -Extension of DIRAC experiment-

本研究的主要目的是在CERN进行PS212 （DIRAC）实验，以测试低能区的非微扰QCD。要彻底了解强子相互作用，必须对理论进行实验检验。虽然在这个区域很难进行可靠的计算，但π-π散射长度的预测精度高于2%。DIRAC实验旨在通过测量A_<2π>原子的寿命，以5%的精度测量π - π散射长度。在这个项目期间，日本小组通过改进实验装置来进行实验。部分实验结果已被分析并发表。该合作项目采用与DIRAC相同的技术，测量由K和π形成的原子的寿命。然而，这种原子产生的横截面要小得多，而且测量需要开发在更大的光束强度下有效的探测器。为解决当前dE/dx计数器的饱和问题，研制了一种可触发的快速硅条计数器，并已研制成功。并研制了用0.28 mmΦ闪烁体代替现有的0.5 mmΦ闪烁体的光纤反射镜，以及采用F1-TDC的快速读出系统。该探测器的效率为98%，空间分辨率为64 μm，时间分辨率优于500 ps，可以用作跟踪装置和触发装置。随着这些计数器的发展和俄罗斯小组开发的微漂移室的发展，使检测A_<Kπ>成为可能，并于2005年12月批准了作为DIRAC扩展进行该实验的项目。认真的准备工作正在进行中。

The principal objective of this study is to carry out PS212 (DIRAC) experiment at CERN to test the non-perturbative QCD in the low-energy region. It is essential to test the theory experimentally to understand thoroughly the hadron interactions. Although is difficult to carry out reliable calculations in this region, the π-π scattering length is predicted with an exceptional precision, better than 2%. DIRAC experiment aims at measuring the pi-pi scattering length with a precision of 5% by measuring the life-time of the A_<2π> atom.During the period of this project, the Japanese group pursued the experiment by improving the experimental setup. Parts of the experimental result have been already analyzed and published.The collaboration undertakes a measurement of the life time of atoms formed with K and π by applying the same technique used in DIRAC. The production cross section of such atoms, however, is much smaller, and the measurement requires the development of detectors efficient in much larger beam intensities.To solve the saturation problem of the current dE/dx counter, a fast silicon strip counter which allows a use in triggering is developed, and now it is ready. Also a scintillating fiber hodoscope using 0.28 mmΦ scintillator in stead of current 0.5 mmΦ one, and a fast readout system using F1-TDC have been developed. The detector has now an efficiency of 98%, spatial resolution of 64 μm together with a time resolution better than 500 ps, and it can be used as a tracking device as well as a triggering device.With the development of these counters together with micro drift chamber developed by the Russian group, the detection of A_<Kπ> became possible, and the project to carry out this experiment as an extension of DIRAC has been approved in December 2005. A serious preparation is in progress.