Weak Decays Of Adoubly-heavy Baryon To Agroud Stste Baryon And A Heavy Meson

Doubly-heavy baryons,which consist of one light and two heavy quarks,are predicted to exist in QCD theory and the quark model.However,in experiments their existence were not established until 2017,when the Large Hadron Collider(LHC)of CERN officially announced the discovery of double charmed baryons ?cc++.The discovery is significant and meaningful.In this thesis,we systematically study the two body nonleptonic weak decays of doubly-heavy baryons,?cc+,?cc+,?cc+,?bc+,?bc0 and ?bc0.The former three particles,?cc+,?cc++and ?cc+,are made up of two charm quarks and one light quark of u,d or s;whereas the last three baryons,?bc+,?bc0and ?bc0,are also consisted of two heavy quarks and one light quark of u,d or s,but one of the heavy quarks is the bottom quark and the other one is the charm quark.As we know,at the charm scale,the hadronic matrix elements of weak transition amplitudes cannot be calculated by many approaches,such as the perturbative QCD approach.The factorization approach can only be used to calculate the little part contribution in transition,but the long distance contributions at the charm scale are very important.In this paper,we study the branching ratios of ?cc++ as well as the decay widths of ?cc++,?cc+,?bc+,?bc0 and ?bc0in a phenomenological way.In calculation,the dynamics of decay processes are divided into two parts,one is the short distance contribution which can be calculated under the hypothesis of factorization,the other is the rescattering mechanism for the long distance contributions.For the long distance contribution,we use the optical theorem to calculate them.Finally,the branching ratios of all decay channels are obtained meanwhile the results are analyzed and discussed.Our results are as follows(1)According to the classification of CKM,we compared all types of decay processes.We found that the contributions of CKM favored decay progresses are generally larger than the contribution of singly CKM suppressed decay progresses and the contribution of doubly CKM suppressed decay progress.Meanwhile,the contribution of doubly CKM suppressed decay processes are the smallest.(2)The branching ratios of all decay channels whose final products are consisted of a baryon and a vector meson are generally bigger than the branching ratios of those decay processes whose final products include a light baryon and a pseudoscalar meson.(3)In the decays of ?cc++?BD/BD*,?cc+BD/BD*and ?cc+?BD/BD*,the channels that have the largest decay branching ratio are ?cc++??+D*+,?cc+??0D*+and ?cc+??0D*+,respectively.We think that the experimenters could successfully discover the double charmed baryons ?cc+and ?+through the latter two decay channels.(4)Based on our analysis,the channels with largest branching ratios of ?bc+,?bc0 and ?bc0 are ?bc+?B*0?+,?bc0?B*?+,and ??B*0?0,respectively.We hope our experimental colleagues to perform a search to find out these doubly-heavy baryons as soon as possible in LHCb.