Measurement Of The Asymmetry Parameter And CP Violation In ?_c~+???~+ Decays

This thesis describes the study of direct charge-parity(CP)violation in ? c ??A?+ decays based on LHCb experimental data.The LHCb experiment at the Large Hadron Collider(LHC)in Europe is dedicated to the study of decays of heavy hadron-s.This work uses a data sample of proton-proton collisions collected by the LHCb experiment in 2016 at a center-of-mass energy of 13 TeV,corresponding to an inte-grated luminosity of 1.67 fb-1.In the Standard Model,? c ?? A?+ proceeds mainly via a tree diagram which exchanges a W+ boson.The predicted CP violation is zero basically,but the contri-bution of charged Higgs particles in some new physical models can lead to sizeable CP violation.We investigates the angular distribution of protons in the cascade de-cay ? c ??? c ?+???p?-,fom which the asymmetry parameter related to parity violation is determined.CP violation parameters are measured by comparing decay asymmetry parameters of ? c ?? and ? c-.In order to increase the signal-to-noise purity of the selected sample of ? c ? decays,we use the multivariate analysis technique in the offline event selection to suppress the combinatorial background.We fit the invariant mass distributions of ? c ? and? c-,respectively,using shapes of signal and physical background determined with simulated data samples.In the angular analysis,the data samples are weighted using the Splot technique to subtract background in the angular distributions.The efficiency as a function of the proton helicity angle is obtained by using simulated samples of the signal decays,and this function is used to obtain efficiency-corrected angular distributions of the signal decays.Finally,theoretical formulas are used to fit the efficiency-corrected angular distributions of ? c ? and ? c-,respectively.The decay asymmetry and CP violation parameters are estimated to be:?? c = ?0.748 ± 0.022,=-0.010±0.009.The systematic uncertainties of this preliminary result need to be further studied and there is significant room for improvement.This study demonstrates the LHCb experiment's capability to perform high-precision measurement of CP Violation in the decay ? c ??.? ? ?.