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

这项研究的主要目的是在欧洲核子研究中心进行PS212(狄拉克)实验，以测试低能区的非微扰QCD。为了彻底理解强子相互作用，必须对该理论进行实验检验。虽然在这个地区很难进行可靠的计算，但π-π散射长度的预测具有超乎寻常的精度，优于2%。狄拉克实验旨在通过测量A&lt；2π&>原子的寿命来测量pi-pi散射长度，测量精度为5%。在该项目期间，日本团队通过改进实验装置进行了实验。部分实验结果已经被分析并发表。合作伙伴通过应用狄拉克所用的相同技术来测量由K和π形成的原子的寿命。然而，这种原子的产生截面要小得多，而且测量需要开发在更大的束流强度下有效的探测器。为了解决当前De/DX计数器的饱和问题，开发了一种用于触发的快速硅条计数器，现在它已经准备好了。还研制了用0.28 mmΦ闪烁体代替现有的0.5 mmΦ闪烁体的闪烁光纤示波器和使用F1-TDC的快速读出系统。该探测器现在的效率为98%，空间分辨率为μm，时间分辨率优于500ps，既可用作跟踪装置，也可用作触发装置。这些计数器与俄罗斯小组开发的微型漂移室一起开发，使A&lt；Kπ&gt；的探测成为可能，并于2005年12月批准了作为狄拉克的延伸进行这一实验的项目。一项严肃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.