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

Abstract

We compute radiative corrections to $Λ_b \to Λ$ from factors, at next-to-leading logarithmic accuracy, from QCD light-cone sum rules with $Λ_b$-baryon distribution amplitudes. Employing the diagrammatic approach factorization of the vacuum-to-$Λ_b$-baryon correlation function is justified at leading power in $Λ/m_b$, 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 ${\cal O}(α_s)$ shift the $Λ_b \to Λ$ 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 $Λ_b \to Λ$ from factors we further investigate several decay observables in the electro-weak penguin $Λ_b \to Λ\, \ell^{+} \ell^{-}$ transitions in the factorization limit (i.e., ignoring the "non-factorizable" hadronic effects which cannot be expressed in terms of the $Λ_b \to Λ$ 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.