关键词： 光锥QCD求和规则, 形状因子, CKM矩阵元

Abstract: The heavy-to-light transition form factors are very important parameters，which play an important role in B-meson decays. The uncertainties of calculation of form factors in light-cone QCD sum rules mainly come from light-cone wave function among which twist-2 and twist-3 wave function make significant contributions to form factors. Now only twist-2 wave function has been systematically analyzed and twist-3 and twist-4 wave function have not satisfactorily determined but twist-4 contribution is very small, therefore, it is twist-3 wave function that cause large uncertainty of form factors. So, through construction adequate chiral current correlation function and consideration of all twist 2 and 4 contribution, the heavy-to-light B→π transitions form factor was calculated in improved light-cone QCD sum rules, and was compared with the result in standard light-cone QCD sum rules. They are consistent with each other, but the uncertainties are eliminated about twist-3 wave function, so the CKM matrix element ｜Vub｜ precisely can be extracted.The contributions of every parameter to uncertainties of calculation result f(q2) are discussed and presented. For example, the contributions of Borel parameter is ±(3～5)%; light-cone wave function ±10%; The higher twist wave functions are less than 5%.

Key words: improved light-cone QCD sum rules, form factor, CKM matrix element