The Semileptonic Decays Of B→πl(?) In The Perturbative QCD Approach

Particle physics,also known as "elementary particle physics" or "high energy physics",is a cornerstone discipline that helps people deepen their understanding of the structure of matter.Standard Model is one of the most successful theories to help people study and explain physical phenomena in particle physics.From 1999 to 2011,two B meson factory experiments were successful.It has provided us with a lot of experimental data.The research of B physics has gradually become a hot spot.B meson physics plays an important role in testing standard model theory or exploring new signs or evidence in new physics.Right now,High energy physics experiments and theoretical studies have entered the "LHC era".LHCb and the future Super-B experiment will push the B meson physics research into a new era.But in theory,up to now,a completely self-consistent method has not been found to calculate the Hadron matrix elements from the first principle of QCD.The perturbation QCD factorization method has its unique advantages in dealing with QCD problems such as transition shape factors and annihilation graphs.So in this article,we use pQCD factorization method to study the B → πl（?） semileptonic decay process.In this paper,the experimental and theoretical status of B meson physics is introduced briefly,then several theoretical calculation methods of Hadron matrix element are discussed,and the basic theoretical framework of pQCD factorization scheme is introduced emphatically.Finally,my work is emphatically introduced.In this paper,we use pQCD factorization scheme to study the B→πl（?） semileptonic decay process,consider the numerical results of form factor of lattice QCD in the large q² energy region,and give the numerical results.In comparison with the experimental values given by BaBar,Belle and other experimental groups,the following conclusions are obtained:（1）For F₀（q²）and F+（q²）,they are equal at q² = 0,but in the large q² region,their dependence on q² is significantly different.（2）For the shape factor from B → π decay,the numerical results under the scheme of pQCD factorization at q² = 0 are in good agreement with those calculated in other theoretical literatures.However,the extrapolated shape factor has a large tendency to be raised in the large q² region,and considering the numerical results of form factor of lattice QCD,the shape factor of the B → πl（?） decay process is effectively depressed in the large q² region.The reliability of shape factor is improved effectively when extrapolating from small q² energy region to large q² energy region.（3）For the semileptonic decay ratio of B →πl（?）,the numerical results under the pQCD factorization scheme are obviously larger than those of the experimental measurements,and there is a σ deviation.After considering the numerical results of the form factor of lattice QCD,the differential decay width is depressed in the large q² region,and the decaying branching ratio is smaller than that obtained under pQCD factorization scheme.The branchhing ratio of the （?）⁰ → π+e-（?）_e decay channel is reduced from 1.57×10^-4 to 1.22×10^-4（1=e,μ）.Compared with the experimental measurements,it is obviously smaller and consistent with a σ deviation.The reliability of the calculation results is obviously enhanced.In the next step,we will consider the higher order correction of the shape factor,so that the theoretical prediction of the decaying branching ratio under pQCD factorization scheme will be in better agreement with the experimental values.