BESⅢ上粲偶素自旋单态的实验研究

Experimental Study of the Spin-singlet Charmonium States at BESⅢ

由于产额较低和探测困难,人们对粲偶素自旋单态(ηc(1S)、hc(1P)和ηc(2S))的认识要远比自旋三重态差。虽然第一个粲偶素的发现是在近40年以前,对粲偶素自旋单态比较精确的测量结果都是最近做出的。北京谱仪(BESIII)于2009年采集了1.06亿ψ(3686)事例,对以上粲偶素自旋单态进行了研究:精确测量了ηc(1S)的共振参数,发现了ηc(1S)振幅与连续态振幅之间的干涉效应,成功解释了ηc(1S)共振曲线不对称现象;首次测量了ψ(3686)→π0hc(1P)的跃迁几率、hc(1P)→γηc(1S)的跃迁几率以及hc(1P)的衰变总宽度,并提高了hc(1P)质量的测量精度;发现了粲偶素的磁偶极跃迁ψ(3686)→γηc(2S),并确定了其跃迁几率。这些结果为理解粲偶素能谱及其产生和衰变机制提供了关键数据。

The knowledge on the spinsinglet charmonium states （η.（IS）, he （1P） and η.（2S）） are poor be cause of the low production rate and the limitation in photon detection. Although the first charmonium state was observed about 40 years ago, only until recently the spinsinglet charmonium states were measured precise ly. Using a data sample of 1.06 x l0s η.（3686） events collected with the BESIII detector at the BEPCII storage ring in 2009, BESIII experiment reported the studies ofthe spinsinglet charmonium states. These include the high precision measurement of the mass and width of % using a model that incorporates interference between the signal amplitude and a nonresonant amplitude; the first measurement of the absolute branching fractions of （3686）ho, and the width of along with an improved measurement of the mass of h ; the first observation of the M1 transition （ 3686 ）- （2S） with a transition rate of These results provide essential information on the understanding of the charmonium states.