Study of CP Violation in the Neutral Kaon System

我们于1996年至1997年在费米实验室进行了KTeV实验，得到了如下结果.通过测量K_L、Ks * + -和^0 ^0衰变的分支分数的两倍比，我们发现CP在衰变本身中被破坏（直接CP破坏）<product><product><product><product>。基于20%的数据，我们获得了初步结果，Re（e '/e）*（28 0*4.1）x 10^<-4>，其与0相差超过6个标准差。这一结果否定了作为CP破坏机制解释理论之一的超弱模型.在K_L * + e+e-衰变中，我们观察到了运动学变量中的第一个CP破坏，即<product>+<product>-面和e+ e-面<product>之间夹角分布的不对称<product>性.我们寻找了以直接CP破坏为主的衰变K_L *<product>^Onunu，并将分支比的最佳上限设定为&lt;5.9x10^7（90%CL）（初步）。我们发现纯CsI和铅/闪烁体夹层探测器满足未来K_*&lt;1@所需的规格<1L>：S1 O&gt;nunu实验。我们举办了一次关于K中CP破坏的国际研讨会，并对未来测量K_L * ^Onunu衰变分支比的实验进行了广泛的讨论。

We ran KTeV Experiment at Fermilab from 1996 to 1997, and obtained following results.1. We found that the CP is violated in the decay itself (direct CP violation), by measuring the double ratio of the branching fractions of K_L, Ks * <product> + <product> -and <product>^0 <product>^0 decays. Based on the 20% of the data, we obtained a preliminary result, Re(e'/e) * (28 0*4.1) x 10^<-4> which is more than 6 standard deviations away from 0. This result rejects the Superweak model which was one of the theories explaining the CP violation mechanism.2. We observed the first CP violation in a kinematical variable, the asymmetry in the distribution of the angle between <product> + <product>- and e+e-planes, in the K_L * <product> + <product> e+e- decay.3. We searched for the decay K_L * <product>^Onunu, which is dominated by direct CP violation, and set the best upper limit on the branching ratio, <5.9x10^7 (90%CL) (preliminary).We also measured the detection inefficiency of photon detectors due to photo-nuclear interactions by using tagged photon beam at KEK Tanashi. We found that pure CsI and lead/scintillator sandwich detectors satisfy the specs necessary for the future K_<1L> * _<1@ : S1O>nunu experiments.We had an international workshop on the CP violation in K, and had an extensive discussion on the future experiments to measure the branching ratio of K_L * ^Onunu decay.