Heavy To Light Pseudo-scalar Meson Transition Form Factors And Decay Studies Inclusively

Heavy to light pseudoscalar meson exclusive decays play an important role in having an better understanding of the standard model （SM）, extracting its parameters and searching for new physics beyond the SM. As compared with inclusive decays, the exclusive decays are clean in experiments, but the corresponding theoretic calculations are difficult due to involving the nonperturbative strong interactions. By using the effective Hamiltonian method, we can separate the perturbative effects from nonperturbative ones, which are represented by the Wilson coefficients and operator matrix elements respectively. For Wilson coefficient, we can use the perturbative method to calculate, and operator matrix element from nonperturbative effects, then we need to find some other methods to deal with. For the heavy baryon or meson containing only one heavy quark （c or b quark）, we can use the heavy quark effective field theory （HQEFT） for processing. In this method, operator matrix elements are expanded by1/MQ （Q denoting heavy quark）, the calculations can be simplified to a large extent.This thesis is mainly devoted to the studies for the heavy to light pseudoscalar meson transition form factors and corresponding exclusive decays by using the light cone sum rules and HQEFT. The main contents are as follows:·Calculation of transition form factor:First, we calculate the Dâ†'K transition form factors to the next leading order of heavy quark expansion in the framework of HQEFT by using the light cone sum rules. In the process of calculation, we consider the K meson light cone distribution amplitudes up to twist3（including2and3particle distribution amplitudes） and SU（3） chiral symmetry breading effects. It is found that the contribution from next leading order of heavy quark expansion is very important, about40%of the contribution from leading order and therefore can not be neglected. Two free parameters are involved in the calculation, et. al. s₀（relating to D meson threshold） and T （Borel transformation parameter）. Since the contributions from leading and next leading order of heavy quark expansion are calculated separately, different values of s₀, T for these two parts are allowed. The uncertainties of transition form factors are mainly come from S₀and T, about12%。·Heavy to light pseudoscalar meson exclusive decays:Based on the transition form factors calculated above, we study the Dâ†'K（?）v decay and calculate the corresponding branching ratios. It is found that the branching ratio for D⁰â†'K-（?）+v is consistent with the current experimental data and that for D+â†'K⁰（?）+v is also compatible with experiments within the uncertainties.