Improved Analysis Of The Rare Decay Processes Of Λ_b

The rare decay process of heavy hadrons is a pure platform for investigation of the strong interaction,as well as verification of the standard model(SM)and searching for new physics beyond the SM.New experiments show that the current theoretical results on the processes Λb→Λγ and Λb→Λl+l-have farely large deviation in comparison with the experimental data.Therefore it is interesting and instructive to reanalyze these channel.In the analysis on the strong interaction with QCD,the key element is to construct the Lagrangian or the Hamiltonian.Therefore it is important to give the corresponding Hamiltonian for a specified process.Meanwhile,a useful nonperturbative method is necessary due to the nonperturbative difficulty of the strong interaction.In this thesis,the light-cone QCD sum rule(LCSR)is adopted for the processes.The key point of this method is to construct the interpolating current with the same quantum number as the hadron and the interaction current to describe the hadron and the interaction.The relative information of the hadron and the process is obtained by calculation of the current-current relation function.In the calculations,the hadronic part is obtained by inserting a complete set of median states,while the theoretical present is gotten through the Operator Product Expansion(OPE),and the nonperturbative effects are expressed as the light-cone distribution amplitudes(LCDAs).In this thesis we use the renewed LCD As of the Λ baryon to analyze the mentioned two processes.Different types interpolating currents may also affect the calculation.Especially for the baryon,there always are several types of interpolating currents which maintain the requirement of the quantum numbers.Meanwhile,the results from different currents cannot be predicted before calculations.We use CZ-type and Ioffe-type interpolating currents to investigate the two processes Λb→Λγ and Λb→Λl+l-.With the calculation of the two-point correlation function,the form factors relative to the processes are obtained.The results are fitted by the dipole formula and are extrapolating to the whole dynamical region.The differential decay width is obtained with the fitted form factors.The analysis shows that the Ioffe-type current has more reliable prediction.Our prediction of the branching ratio for the process Λb→Λγ is Br(Λb→Λγ)=(7.38-0.39+0.40)×10-6,which is well accordant to the new experiments.In the same framework,we also get the branching ratio of the process Λb→Λl+l-is Br(Λb→Λl+l-)=1.20×10-6,which is well consistent with data from PDG and other theoretical predictions.