Phenomenological Study Of The B_s?Kl~+l_-Semileptonic Decays

The particle physics studies the basic structures of matter,at the level of quark and leptons,focus on the structure and the property of the fundamental particles,as well as the law of the basic interactions.The standard model(SM)is the most successful theory to help people to study and explain the phenomena in particle physics.From 1999 to 2011,the two B meson experiments in US and Japan(BaBar and Belle Collaboration)collected a large amount events of the production and decays of B meson pairs,and made a great contribution in the precision test of the SM and in the searching for the possible evidence or signals of the new physics beyond the SM.Nowadays,the theoretical studies and the high energy experimental measurements are going on smoothly in the so-called "LHC era".In the field of the heavy flavor physics,the LHCb?Belle-? and BES-? experiments have made a great progress and push the studies of the beauty and charm physics into a new period of rapid development.Up to now,however,there exist also many difficulties.Taking B meson physics as an example,we have not found a completely self-consistent method based the first principles of QCD to calculate the hadronic matrix elements of the relevant transitions.Among the major factorization methods,the perturbative QCD(PQCD)factorization approach has its unique advantage in calculating the hadron matrix elements.In the review part of this thesis,we first give a simple introduction for the framework of the heavy flavor physics and current status of B meson physics,and then present some introductions for several main factorization methods,specifically for the PQCD factorization approach.In the work part,we studied the semileptonic decays B0s?Kl+l-with l=(e,?,?)by employing the PQCD factorization approach,made the analytical and numerical calculations,and compared our results with those obtained based on other different theoretical methods because of the absence of the measured values.Based on our calculations and analysis we found the following points:(1)For the form factors F0(q2)and F+(q2),they are equal at q2=0,but their q2-dependence in the large q2 region are quite different.F+(q2)has a stronger dependence on q2 than F0(q2).Within the errors,the PQCD predictions for F0,+(q2)have only a little difference with those from other factorization approaches.(2)We used the pole model and the BZ parameterized method to make the extrapolation,and the numerical results have a small difference from the predictions of other methods.Our PQCD predictions for the branching ratios of the considered decays is slightly larger than those in former literatures,mainly due to the variations of the input parameters or the wave functions.(3)When we use the exponential function to make the extrapolation,the difference between our PQCD predictions for the branching ratio and those from other literatures will be decreased effectively.The choice of fitting function had a certain influence on the numerical result.The exponential function have a good depression effect on the numerical predictions.These theoretical results will be tested by the future experimental measurements.In the last chapter,we give some discussions and a summary of this paper,we expect the great progress of the theoretical studies and experimental measurements in the near future.