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重到轻跃迁形状因子是非常重要的参量 ,它在B介子衰变中起重要作用 .在光锥QCD求和规则中 ,形状因子的计算结果的不确定性主要来自于光锥波函数 ,twist- 2 ,twist- 3的波函数是主要贡献的波函数 .现在仅有twist - 2的波函数被系统地分析并较精确地确定下来 .然而 ,对twist- 3,twist- 4的波函数确定不够好 .但twist- 3波函数对形状因子的贡献与twist- 2波函数贡献相当 ,Twist- 4波函数贡献很小 ,这样twist- 3波函数给计算结果带来较大的不确定性 .为此 ,通过构造手征流关联函数 ,消除了twist- 3波函数的不确定性所带来的影响 ,用改进的光锥QCD求和规则计算B→π跃迁形状因子 ,与标准的光锥QCD求和规则的结果基本吻合 ,从而更能精确地抽取CKM矩阵元 |Vub|.各参数对计算结果f(q2 )的不确定度的影响范围是 :Borel质量参数M2 的影响为± (3～ 5 ) % ,光锥波函数± 10 % ,高扭度波函数的影响不超过 5 % .
The light-to-light transition shape factor is a very important parameter and plays an important role in decay of the B meson.In the light cone QCD summation rule, the uncertainty of the shape factor calculation results mainly from the light cone function, the twist- The wave function of twist - 3 is the main contribution of the wave function. Now only the wave function of twist - 2 is systematically analyzed and more accurately determined. However, the determination of the wave function of twist - 3 and twist - 4 is insufficient However, the contribution of twist-3 wave function to the shape factor is comparable to that of the twist-2 wave function and the contribution of the Twist-4 wave function is small, so that the twist-3 wave function brings greater uncertainty to the calculation result By means of constructing the chiral flow correlation function, the influence of the uncertainty of the twist-3 wave function is eliminated. The shape factor of the B → π transition is calculated by using the improved light cone QCD summation rule, which is compared with the standard light cone QCD Vub | The influence of each parameter on the uncertainty of calculation result f (q2) is: The influence of Borel mass parameter M2 is ± (3 ~ 5)%, light cone function ± 10%, high-twist wave function No more than 5%.