X-ray Spectrocopy of Kaonic Atoms

通过测量高能氢原子的X射线，研究了低能强相互作用。这个实验是在韩国KEK的12GeV质子同步加速器上进行的。这个实验的重要性早已被认识到，之前在70年代末的S和80年代初的S有过3次实验。然而，由于实验的困难，以及由于Kaon束流的小流量，没有人能成功地观测到Kaon氢X射线。为了克服困难，由于束流粒子产生的大本底，以及小的X射线产额，我们开发了新的方法来抑制X射线本底，提高信噪比。首先，通过测量反应顶点来抑制本底，以及通过选择源自氢靶的事件，以及ii)通过应用事件标记来选择具有2个处于最终状态的带电介子的事件。我们还开发了一种由60个Si(Li)晶体组成的新型X射线探测器系统，工作在低温氢气中。用气体靶代替液体，有助于提高信号背景比。在第一年，我们集中在探测器的开发和建设上。这家日本集团主要致力于氢靶、束流计数器、硅(Li)探测器以及总体基础设施方面的工作。加拿大团队致力于开发和建造圆柱形顶点室和水切伦科夫探测器，这两个探测器对于减少背景都是必不可少的。完成的探测器被运送到KEK，并在那里组装。1994年，我们开始使用Kaon束调试系统，到1994年底，我们开始采集数据。初步分析表明，我们已经成功地观测到了高介子氢X射线，尽管我们需要收集更高的统计数据才能得出最后的结论。

Strong interaction at low energy was studied by measuring X-rays of kaonic hydrogen atoms. The experiment was set up at the 12 GeV proton synchrotron of KEK.The importance of this experiment has long been recognized, and there were 3 previous trialsin late 70's and early 80's. However, due to experimental difficulties and due also to the small flux of kaon beam, nobody has succeeded in the observation of the kaonic hydrogen X-rays.In order to overcome difficulties, due to the large background caused by beam particles, and also to the small X-ray yields, we developed novel methods to suppress the X-ray background, and to enhance the signal to noise ratio.Namely, background was suppressedby i) measuring the reaction vertex, and by selecting the events originating from the hydrogen target, and ii) by applying event tagging to select events with 2 charged pions in the final state. We also developed a novel X-ray detector system consisting of 60 Si (Li) crystals, operating in a low-temperature hydrogen gas. The use of gas target, instead of liquid, should help improve signal to background ratio.In the first year, we concentrated on the detector development and construction. The Japanese group worked mostly on the hydrogen target, beam counters, Si (Li) detectors, and on the infrastructure in general. The Canadian team worked on the development and construction of the cylindrical vertex chambers and water Cherenkov detectors, both of which were essential in reducing the background. The completed detectors were transported to KEK,and were assembled there.In 1994, we started to debug the system using the kaon beam, and by the end of 1994 we started to take data. Preliminary analysis exhibited that we have succeeded in observing the kaonic hydrogen X-rays, although we need to collect higher statistics in order to draw final conclusions.