中性B介子衰变中时间依赖CP破坏的实验研究进展  

Advances in experimental study of time-dependent CP violation in neutral B meson decays

作　　者：谢跃红 张黎明 Yuehong Xie;Liming Zhang(Key Laboraoy of Quark and Lepon Physics(MOE),Insituteof Particle Physics,Central China Normal University Wuhan 430079,China;Department of Engineering Physics,Tsinghua Universiy Beijing 100084,China)

机构地区：[1]华中师范大学粒子物理研究所,夸克与轻子物理教育部重点实验室,武汉430079 [2]清华大学工程物理系,北京100084

出　　处：《科学通报》2024年第31期4577-4589,共13页Chinese Science Bulletin

基　　金：国家自然科学基金(12275100)资助。

摘　　要：电荷共轭-宇称联合变换对称性的破坏简称CP破坏.中性B介子系统具有正反粒子振荡和CP破坏随时间变化等独特性质,提供了探索CP破坏机制的理想窗口.B介子工厂发现了B^(0)介子衰变的CP破坏,对粒子物理标准模型中Cabibbo-Kobayashi-Maskawa(CKM)夸克混合机制的确立发挥了关键作用.大型强子对撞机底夸克(Large Hadron Collider beauty,LHCb)实验在深入研究B^(0)介子CP破坏的同时,开展了B_(s)^(0)介子振荡和CP破坏的开拓性研究,显著提升了B^(0)介子混合相角2β、B_(s)^(0)介子混合相角φ_(s)与振荡参数Δm_(s)、CKM相角γ的测量精度,发现了B_(s)^(0)→K^(+)K^(-)衰变中存在显著的CP破坏.这些研究成果极大地丰富了我们对夸克味道改变和CP破坏现象的认知,对精确检验标准模型、寻找超出标准模型的新物理现象具有重要意义.本文在回顾中性B介子CP破坏研究历程的基础上,简要介绍时间依赖CP破坏的测量方法与要素,重点总结十多年来LHCb实验在中性B介子CP破坏研究方面取得的阶段性成果和重要进展,展望LHCb探测器升级为本研究领域带来的新机遇.Neutral B mesons exhibit fascinating features of flavour oscillation and time-dependent CP violation,providing an ideal window to probe the origin and mechanism of CP violation.The LHCb experiment at the Large Hadron Collider is well suited for study of time-dependent CP violation in neutral B meson decays,owing to the copious production of B^(0) and B_(s)^(0)mesons,and the excellent performance of the LHCb detector in tracking,vertexing and particle identification.In the first two running periods,the LHCb experiment has accumulated a large sample of proton-proton cpllision data collected at center-of-mass energies of 7,8 and 13 TeV,corresponding to an integrated luminosity of 9 fb^(-1).Fruitful study of timedependentn CP violation in both B^(0) and B_(s)^(0) meson decays has been carried out at LHCb.In the B^(0) sector,the LHCb experiment has overtaken the B factories,achieving the highest precision in a series of key measurements.A recent study of B^(0)→J/ΨK~S_0 and B^(0)→Ψ/(2S)K_(S)^(0) decays using the full Run 1 and Run 2 sample gives sin2β=0.717 ±0.013 ± 0.008,which are consistent both with previous results from BaBar,Belle and LHCb and with the standard model predictions.The B^(0) mass difference is measured to be Δm_(d)=0.5050±0.0021 ±O.OO1Ops^(-1) using B^(0)→D^((*)-)μ^(+)υ_(μ) decays.CP-violating parameters for the decay B^(0)→π~+π~-are measured to be S_(ππ)=-0.672±0.034,C_(ππ)=-0.320±0.038.The B_(s)^(0) sector was largely unexplored before the LHC.The LHCb experiment has made vast efforts to study B_(s)^(0)oscillation and time-dependent CP violation.The B_(s)^(0) mass difference has been very precisely determined to beΔm_s=17.7683 ± 0.0051 ± 0.0032 ps^(-1) using B_(s)^(0)→D_s~-π~+ decays.The sign of the B_(s)^(0) decay width difference ΔΓ_(s) is determined to be positive using part of 2011 data,and the two-fold ambiguity in the previous measurements of φ_(s) and ΔΓ_(s) is completely resolved.The B_(s)^(0) mixing phase φ_(s) is a core measurement at LHCb,which has

关 键 词：CP破坏 中性B介子 CKM矩阵 标准模型 LHCb实验 大型强子对撞机 

分 类 号：O572.33[理学—粒子物理与原子核物理]