Study On Λ_c~+ Decay In BESⅢ Experimen

Λc+ charmed baryon consists of a heavy charm quark and two light quarks.In the charmed baryon family,it is the lightest baryon.The study of the weak decay of Λc+ charmed baryons can help us to better understand the mechanisms of weak and strong interactions.In addition,the members of the charmed baryon family are rich and most of them will decay toΛc+,so a clear understanding of Λc+ is important significance to explore the properties of other charmed baryons.Based on 4.5fb-1 e+e-annihilation data samples at(?)=4599.534698.82 MeV accumulated with the BESⅢ detector,we firstly measure the branching fractions of Λc+→nπ+π0,Λc+→nπ+π-π+ and Λc+→nK-π+π+.We measure the branching fractions for two Cabibbo-suppressed decays B(Λc+→nπ+π0)=(0.64±0.09±0.02)%with a statistical significance of 7.9σ,and B(Λc+→nπ+π-π+)=(0.45±0.07±0.03)%with a statistical significance of 7.8σ,plus a Cabibbo-favored decay B(Λc+→nK-π+π+)=(1.90±0.08±0.09)%with a statistical significance of larger than 10a.This results will be helpful for us to further test the isospin symmetry and SU(3)symmetry in the charmed baryon sector.The branching fraction of inclusive decay Λc+→Λ+X is also measured,which is B(Λc+→Λ+X)=(38.48±0.38±0.38)%.Our result is consistent with the published result within the uncertainty range,but the accuracy is nearly five times higher than that.CP violation is one of the conditions to explain the asymmetry of matter and antimatter in the universe.However,the prediction of CP violation in the standard model is not enough to describe the asymmetry of matter and antimatter that we have observed at present,which means that there are new sources of CP violation beyond the standard model.CP violation is only observed in meson systems,and the CP violation in baryon sector has not been found experimentally.The visible matter in the universe is mainly composed of baryons,so the study of CP violation in charmed baryon decays provides a good opportunity to test the standard model and find new physics.A large number of Λc+ charmed baryons can be produced in the BESⅢ,which creates a good condition for studying the CP violation in charmed baryons.We firstly measure the polarization parameters of inclusive decays Λc+→Λ+X and Λc-→Λ+X.These polarization parameters are measured to be P(Λc+→Λ+X)=-0.399±0.047±0.013 and P(Λc-→Λ+X)=0.294±0.046±0.013,respectively.We calculate the CP violation parameter to be ACPα(total)=0.13±0.10±0.03,and did not find any obvious CP violation.