标题： 从QCD轻锥求和规则中得到的$Λ_b \to Λ$形式因子的微扰修正 显示英文标题

标题： Perturbative Corrections to $Λ_b \to Λ$ Form Factors from QCD Light-Cone Sum Rules

摘要： 我们从因子出发，在次领头对数精度下计算了$\Lambda_b \to \Lambda$的辐射修正，使用QCD光锥求和规则与$\Lambda_b$重子分布幅度。 采用图解方法，真空到$\Lambda_b$重子关联函数的因子分解在$\Lambda/m_b$的主导幂次下得到验证，借助区域方法。 进入因子分解公式的硬函数与从QCD到软-胶子有效理论的重子到轻子电流的相应匹配系数相同。 从消除硬胶子涨落中得到的普遍喷注函数相比真空到$B$介子关联函数的因子分解表达式中的喷注函数表现出更丰富的结构。 基于QCD重 summation 改进的求和规则，我们观察到在${\cal O}(\alpha_s)$处的微扰修正显著地改变了大反冲情况下$\Lambda_b \to \Lambda$从因子，并且主要贡献来自于次领头阶喷注函数，而不是硬系数函数。 手头有来自因子的$\Lambda_b \to \Lambda$的求和规则预测，我们进一步研究了在因子化极限下（即忽略无法用来自因子的$\Lambda_b \to \Lambda$表达的“非因子化”强子效应）电弱penguin$\Lambda_b \to \Lambda \, \ell^{+} \ell^{-}$转换中的几个衰变可观测量，包括轻子对的不变质量分布、二轻子系统中的正向-反向不对称性以及轻子区的纵向极化分数。 显示英文摘要

摘要： We compute radiative corrections to $\Lambda_b \to \Lambda$ from factors, at next-to-leading logarithmic accuracy, from QCD light-cone sum rules with $\Lambda_b$-baryon distribution amplitudes. Employing the diagrammatic approach factorization of the vacuum-to-$\Lambda_b$-baryon correlation function is justified at leading power in $\Lambda/m_b$, with the aid of the method of regions. Hard functions entering the factorization formulae are identical to the corresponding matching coefficients of heavy-to-light currents from QCD onto soft-collinear effective theory. The universal jet function from integrating out the hard-collinear fluctuations exhibits richer structures compared with the one involved in the factorization expressions of the vacuum-to-$B$-meson correlation function. Based upon the QCD resummation improved sum rules we observe that the perturbative corrections at ${\cal O}(\alpha_s)$ shift the $\Lambda_b \to \Lambda$ from factors at large recoil significantly and the dominant contribution originates from the next-to-leading order jet function instead of the hard coefficient functions. Having at hand the sum rule predictions for the $\Lambda_b \to \Lambda$ from factors we further investigate several decay observables in the electro-weak penguin $\Lambda_b \to \Lambda \, \ell^{+} \ell^{-}$ transitions in the factorization limit (i.e., ignoring the "non-factorizable" hadronic effects which cannot be expressed in terms of the $\Lambda_b \to \Lambda$ from factors), including the invariant mass distribution of the lepton pair, the forward-backward asymmetry in the dilepton system and the longitudinal polarization fraction of the leptonic sector.