Advances in experimental study of time-dependent CP violation in neutral B meson decays
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 B0 and B0 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 collision data collected at center-of-mass energies of 7,8 and 13 TeV,corresponding to an integrated luminosity of 9 fb.Fruitful study of time-dependent CP violation in both B0 and B0s meson decays has been carried out at LHCb.In the B0 sector,the LHCb experiment has overtaken the B factories,achieving the highest precision in a series of key measurements.A recent study of B0 → J/ψK0S and B0 → ψ(2S)K0S 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 B0 mass difference is measured to be Δmd=0.5050±0.0021±0.001 0ps-1 using B0 → D(*)-μ+vμ decays.CP-violating parameters for the decay B0 →π+Ω-are measured to beSππ=-0.672±0.034,Cππ=-0.320±0.038.The B0s sector was largely unexplored before the LHC.The LHCb experiment has made vast efforts to study Bs0 oscillation and time-dependent CP violation.The B0s mass difference has been very precisely determined to beΔms=17.7683±0.0051±0.0032ps-1 using B0 → D-π+decays.The sign of the Bs0 decay width difference ΔΓs is determined to be positive using part of 2011 data,and the two-fold ambiguity in the previous measurements of φs and ΔΓs is completely resolved.The B0s mixing phase φs is a core measurement at LHCb,which has been extensively pursued using tree-level b → c(c)s decays,such as B0s → J/ψφ and Bs0 → J/ψπ+Ω-.The latest update of the Bs0 → J/ψφ analysis using the full Run 1 and Run 2 data sample leads to φs=-0.039±0.022±0.006 rad and ΔΓs=0.0845±0.0044±0.0024 ps-1,which are the most precise measurements and consistent with the standard model predictions.Vanishing time-dependent CP violation is found in several loop-level b → s transitions,such as B0s → φφ and B0s →φγ,as expected in the standard model.Nonzero time-dependent CP asymmetry in Bs0 meson decays was first observed by LHCb in the process B0s → K+K-,which receives sizable contributions from both tree-level and loop-level diagrams.The latest LHCb measurements of CP-violating parameters in B0s→K+K-decays are SKK=0.139±0.032 and CKK=0.172±0.031.Time-dependent CP violation in B0s → D(±)sK±decays is measured by LHCb and used to determine the CKM angle y using the measuredφs value,yielding γ=(74±11)°,which is in good agreement with other γ determinations.These findings have greatly enriched our understanding of flavour physics and CP violation,and made huge impacts on tests of the standard model.The global CKM analysis that includes the recent high-precision LHCb measurements confirms the validity of the CKM mechanism and significantly improves precision of the CKM parameters.The LHCb experiment entered the third running period in 2022 with the recently upgraded1detector.Looking ahead,LHCb aims to collect 50 fb of data in the coming decade and eventually accumulate 300 fb-1 after a phase-2 upgrade.With such massive amount of data,many key measurements of CP violation and CKM elements will be measured with unprecedented precision.For example,using 50(300)fb-1 of data,LHCb will be able to measure sin2β with a precision of 0.006(0.003),the B0s mixing phase φs with a precision of 0.008(0.004)rad,the CP-violating phase in B0s → φφ with a precision of 0.026(0.011)rad,and the CKM angle y in B0s → D+sK-decays with a precision of 4.4°(1.5°).Furthermore,time-dependent CP violation in certain heavily-suppressed decays of neutral B mesons,such as B0 →K0sμ+µ-,B0s → φμ+μ-,B0 → ρ0μ+μ-,B0 → ρ0γ and B0s → μ+μ-,will become accessible at LHCb,offering new opportunities for testing the standard model and probing new physics.
CP violationneutral B mesonsCKM matrixstandard modelLHCb experimentLarge Hadron Collider
万方数据
维普
