LHCb上双重味重子的实验研究进展  

Experimental study on the doubly heavy baryons at LHCb:A review

作　　者：何吉波 尹航 Jibo He;Hang Yin(School of Physical Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;Hangzhou Institute for Advanced Study,University of Chinese Academy of Sciences,Hangzhou 310024,China;Institute of Particle Physics,Central China Normal University,Wuhan 430079,China)

机构地区：[1]中国科学院大学物理科学学院,北京100049 [2]国科大杭州高等研究院,杭州310024 [3]华中师范大学粒子物理研究所,武汉430079

出　　处：《科学通报》2024年第31期4550-4557,共8页Chinese Science Bulletin

基　　金：国家重点研发计划(2017YFA0402102)资助。

摘　　要：本文介绍了LHCb实验上双重味重子的实验研究进展.LHCb实验组利用2016年采集的质子-质子对撞数据,通过中国粒子物理理论家建议的Ξ_(cc)^(++)→Λ_(c)^(+)K^(-)π^(+)π^(+)衰变道观测到由两个较重的粲夸克和一个较轻的上夸克组成的双粲重子Ξ_(cc)^(++),并测得其质量为3621.40±0.72(stat)±0.27(syst)±0.14(Λ_(c)^(+))Me V/c^(2).在此基础上,测得Ξ_(cc)^(++)的寿命为0.2560.022+0.024(stat)±0.014(syst)ps,确认了该粒子主要通过弱相互作用进行衰变的特性;测量了在LHCb探测器接收度范围内Ξ_(cc)^(++)与Λ_(c)^(+)重子产生截面的比值和Ξ_(cc)^(++)→Λ_(c)^(+)K^(-)π^(+)π^(+)衰变分支比的乘积;观测到了Ξ_(cc)^(++)→Ξcπ^(+)和Ξ_(cc)^(++)→Ξc'+π^(+)等新衰变道;联合利用Ξ_(cc)^(++)→Λ_(c)^(+)K^(-)π^(+)π^(+)和Ξ_(cc)^(++)→Ξ_(c)^(+)π^(+)衰变道以及更多实验数据,进一步提升了Ξ_(cc)^(++)重子的质量测量精度.LHCb实验组也利用2011~2018年间采集的所有质子-质子对撞数据,通过Ξ_(cc)^(+)→Λ_(c)^(+)k-π^(+)和Ξ_(cc)^(+)→Ξ_(c)^(+)π^(+)π^(-)过程搜寻了单电荷双粲重子Ξ_(cc)^(+),使得信号灵敏度相比以往结果提高了一个数量级,观测到了Ξ_(cc)^(+)重子存在的迹象;寻找了奇异双粲重子Ω_(cc)^(+),以及含底夸克和粲夸克的3种双重味重子Ξ_(bc)^(+)、Ξ_(cc)^(0)、Ω_(bc)^(0),观察到奇异双粲重子Ω_(cc)^(+)和带电双重味重子Ξ_(bc)^(+)的迹象.这些研究成果开辟了探索强子结构与性质的一个新窗口,将有助于加深对强相互作用本质和强子结构理论的理解.The doubly heavy baryons are formed by two heavy quarks and one light quark,as predicted by the quark model.They are expected to have different internal structures than those of the normal baryons such as the proton and the neutron,therefore have unique properties.Study and search for the doubly heaw baryons is one of the key research topics for both the theoretical and experimental particle physics.The LHCb experiment is one of the four large ones on the Large Hadron Collider at CERN.It has excellent vertexing,tracking and particle-identification performances,and a flexible and efficient trigger system,which make it an ideal place to perform experimental studies of the doubly heaw barvons.Using the proton-proton collision data collected by the LHCb experiment in 2016,the doubly charmed baryon consisting of two charm quarks and one up quark,the Ξ_(cc)^(++) baryon,has been discovered for the first time with the decay modeΞ_(cc)^(++)→Λ_(c)^(+)K^(-)π^(+)π^(+) as suggested by the Chinese theorists.Its mass has been measured to be 3621.40±0.72(stat)±0.27(syst)±0.14(Λ_(c)^(+)) MeV/c^(2).Its lifetime has been measured to be 0.256_(-0.022)~(+0.024)(stat)±0.014(syst) picosecond.Its production crosssection times the branching fraction of the Ξ_(cc)^(++)→Λ_(c)^(+)K^(-)π^(+)π^(+) decay relative to that of the Λ_(c)^(+) baryon is measured to be(2.22±0.27±0.29) × 10-4 in the LHCb acceptance.Such discovery is also confirmed with another decay mode of the doubly charmed baryon Ξ_(cc)^(++)→Ξ_(c)^(+)π^(+).The third decay mode Ξ_(cc)^(++)→Ξ_c~('+)π^(+) has been observed and its branching fraction is measured relative to the Ξ_(cc)^(++)→Ξ_(c)^(+)π^(+) decay.The Ξ_(cc)^(++) mass measurement has been updated with both Ξ_(cc)^(++)→Λ_(c)^(+)K^(-)π^(+)π^(+)and Ξ_(cc)^(++)→Ξ_(c)^(+)π^(+) decays and using the proton-proton collision data taken by the LHCb experiment from 2016 to 2018,and the precision has been improved by a factor of two.Using all the proton-proton collision data taken by th

关 键 词：夸克模型 双重味重子 LHCb实验 质量测量 寿命测量 产生测量 

分 类 号：O572.33[理学—粒子物理与原子核物理]