BESIII Experimental Study On The Branch Ratio Of Thorium Decay

Λ_c⁺ is the ground state of charmed baryon,it’s consisted with three quarks,one heavy charm quark and two isospin symmetric light quarks.Since the ground stateΛ_c⁺was first observed at the Mark II experiment in 1979,only about 60%of its decays have been accounted for,lots of are still remain unknown.Most of the excitedΛ_c or∑_c eventually decays to Λ_c⁺,and most of the Λ_b decays also involves Λ_c⁺.So the precise measurement of Λ_c⁺ is important for the measurement of Λ_b,Λ_c and ∑_c.Since the Λ_c⁺ is the ground state of charmed baryon,it can only decay through weak process,so the study of its decay rates can help our understand the dynamics of charmed baryon decays and can also test the theoretical model of the non-pertubative QCD.Based on the data collected in the e⁺e^-collision at the center-of-mass energy of 8^1/2= 4.6 GeV and using the single-tag method,we measured some Λ_c⁺ decay modes which involves Σ⁺ in the final state,for the Λ_c⁺→Σ⁺η’ was first measured,other results are consisted with the world average value.Unlike the charmed mesons,the W-exchange contributions in charmed baryons is neither helicity nor color suppressed.So W-exchange contributions are of crucial importance for the description of non-leptonic charm baryon decay.Using the BE-SⅢ date taken at 8^1/2= 4.6 GeV and adopting the double tag technique,we measure the absolute branching fractions of the two W-exchange only process Λ_c⁺→（?）⁰K⁺and Λ_c⁺→（?）（1530）^*0K⁺,the results is better than the current PDG value.