Belle实验发现新粲重子存在的迹象  

Evidence of a new excited charmed baryon at Belle

作　　者：李洋 李郁博 沈成平 LI Yang;LI Yu-Bo;SHEN Cheng-Ping(Institute of Modern Physics,Fudan University,Shanghai 200433,China)

机构地区：[1]复旦大学现代物理研究所,上海200433

出　　处：《物理》2023年第4期249-253,共5页Physics

基　　金：国家自然科学基金(批准号:11975076,12161141008,12135005)资助项目。

摘　　要：粲重子是含有粲夸克的一类重子。粲重子存在很丰富的激发态,粲重子谱的研究对理解轻夸克在含重夸克系统中的动力学行为,以及检验重夸克对称性和轻夸克手征对称性具有重要意义。Λc^(+)是质量最轻的粲重子,它是由一个粲夸克、一个上夸克和一个下夸克构成的同位旋单态。最近,日本的Belle实验利用在Υ(4S)中心质量采集的772×10^(6)对BB介子样本,对B0→Σc(2455)^(0,++)π^(±)p^(-)衰变过程进行了研究,并在Σc(2455)^(0,++)π^(±)的不变质量谱上发现了一个新的共振结构。在考虑系统误差后,该共振结构最保守的信号显著性为4.2倍标准偏差。这意味着,该结构的形成源于统计涨落和各种系统误差的概率不足0.002%。Belle实验测得这个新结构的质量为(2913.8±5.6±3.8)MeV/c2,宽度为(51.8±20.0±18.8)MeV。虽然这个新结构的性质目前还不完全清楚,但它很符合新的Λc激发态的性质,暂时被命名为Λc(2910)^(+)。A charmed baryon is a kind of baryon containing at least one charm quark.There exist abundant excited charmed baryons,and the study of charmed baryon spectroscopy is very important for understanding the dynamics of light quarks in the environment of a heavy quark,and for testing heavy-quark symmetry and the chiral symmetry of light quarks.TheΛc^(+)baryon is the lightest charmed baryon,which is an isospin singlet composed of one charm quark,one up quark and one down quark.Very recently,using a data sample of 770 million BB events collected atΥ(4S)resonance in the Belle experiment,Japan,studies were performed on the decay B0→Σc(2455)^(0,++)π^(±)p^(-).A new structure has been found in the invariant mass distribution ofΣc(2455)^(0,++)π^(±)with a significance of 4.2σincluding systematic uncertainty,which means that the probability of the emergence of this structure due to statistical fluctuation and various uncertainties is less than 0.002%.Its mass and width are measured to be(2913.8±5.6±3.8)MeV/c2 and(51.8±20.0±18.8)MeV,respectively.No known excited charmed baryon can match the observed new structure.It is probably a new excitedΛc baryon,tentatively named asΛc(2910)^(+).

关 键 词：Belle实验 粲重子 Λc激发态 Σc激发态 Λc(2910)^(+) 

分 类 号：O572.33[理学—粒子物理与原子核物理]