NLL QCD contribution of the Electromagnetic Dipole operator to B-> X_s gamma gamma

Details NLL QCD contribution of the Electromagnetic Dipole operator to B-> X_s gamma gamma NLL QCD contribution of the Electromagnetic Dipole operator to B-> X_s gamma gamma

2011-10-06

arxiv.org/abs/1110.1251v1

Phys. Rev. D 85, 014020 (2012)

Physics

High Energy Physics

High Energy Physics - Phenomenology

22 pages, 6 figures

Scientific paper

10.1103/PhysRevD.85.014020

We calculate the set of O(alpha_s) corrections to the double differential decay width dGamma_77/(ds_1*ds_2) for the process B -> X_s gamma gamma originating from diagrams involving the electromagnetic dipole operator O_7. The kinematical variables s_1 and s_2 are defined as s_i=(p_b - q_i)^2/m_b^2, where p_b, q_1, q_2 are the momenta of b-quark and two photons. While the (renormalized) virtual corrections are worked exactly for a certain range of s_1 and s_2, we retain in the gluon bremsstrahlung process only the leading power w.r.t. the (normalized) hadronic mass s_3=(p_b-q_1-q_2)^2/m_b^2 in the underlying triple differential decay width dGamma_77/(ds_1*ds_2*ds_3). 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 s_3, 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.

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