2011/10/06 by H. M. Asatrian, C. Greub, A. Kokulu +1 · 2 citations
Physics and Astronomy · #hep-ph #hep-ex
paper · pdf · doi:10.1103/physrevd.85.014020
published as Phys. Rev. D 85, 014020 (2012) · 22 pages, 6 figures
arxiv created 2011/10/06 · arxiv updated 2012/01/23
We calculate the set of O(alphas) corrections to the double differential decay width dGamma77/(ds1*ds2) for the process B -> Xs gamma gamma originating from diagrams involving the electromagnetic dipole operator O7. The kinematical variables s1 and s2 are defined as si=(pb - qi)2/mb2, where pb, q1, q2 are the momenta of b-quark and two photons. While the (renormalized) virtual corrections are worked exactly for a certain range of s1 and s2, we retain in the gluon bremsstrahlung process only the leading power w.r.t. the (normalized) hadronic mass s3=(pb-q1-q2)2/mb2 in the underlying triple differential decay width dGamma77/(ds1*ds2*ds3). The double differential decay width, based on this approximation is free of infrared- and collinear singularities when combining virtual- and bremsstrahlung corrections. The corresponding results are obtained analytically. When retaining all powers in s3, the sum of virtual- and bremstrahlung corrections contains uncanceled 1/epsilon singularities (which are due to collinear photon emission from the s-quark) and other concepts, which go beyond perturbation theory, like parton fragmentation functions of a quark or a gluon into a photon, are needed which is beyond the scope of our paper.