用联合D^0和D^+单双标记测定分支比的方法

A Method of Combined D^0 and D^+ Single and Double Tags to Measure Their Branching Fractions and Its Application

报道了用“联合D0 和D+单双标记”测定衰变分支比的方法 .基于北京谱仪 (BES)在北京正负电子对撞机 (BEPC)质心系能量s =4 .0 3GeV处获取的数据 ,利用联合D0 和D+单双标记的方法 ,可以测定D0 和D+介子单举和遍举衰变分支比 .作为该方法的应用举例 ,利用BES实验组发表的数据 ,在 90 %置信度的情况下 ,测得D+→e+ν衰变过程分支比的上限为Br(D+→e+ν) <1 .6% .此上限值与BES曾发表的结果一致 .

A method of combined D 0 and D + single and double tags to measure their branching fractions is reported. With this method, we can measure the inclusive and exclusive branching fractions of D 0 and D + based on the data taken at s=4.03GeV using BES detector at BEPC collider. As well known, it is very difficult to study D physics with the data taken at s=4.03GeV. Compared with the data taken at s=3.77GeV, where it is just at the threshold of the pure pairs of D + D - and D 0 0 productions. While at s=4.03 GeV D * and D * * can also be produced and then the so-called contaminated final states D + 0 and D -D 0 can be produced via the cascade decays of the D *+ to charged and neutral D. This makes some trouble for the study. The key to solve this problem is how to determine the ratios β, which denotes the recoil 0 production agaist the tagged D +, and η, which denotes the recoil D - production agaist the tagged D 0. We developed the double tag method and single tag method to determine these two parameters, and compared them with cross section method developed by us before. They are consistent with each other within errors, so that the validity of this method was proved. As an example of its application, we set the upper limit for D +→e +ν decay to be Br(D +→e +ν)<1.6% at 90% C. L.. This value is consistent with that BES Collaboration published.