Improved analysis of the (O7, O7) contribution to B ̄→ Xsγγ at O (αs)

Asatrian, H. M.; Greub, Christoph; Kokulu, Ahmet (2017). Improved analysis of the (O7, O7) contribution to B ̄→ Xsγγ at O (αs). Physical review. D - particles, fields, gravitation, and cosmology, 95(5), 053006. American Physical Society 10.1103/PhysRevD.95.053006

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he present study is devoted for an improved analysis of the self-interference contribution of the electromagnetic dipole operator O7 to the double differential decay width dΓ=(ds1ds2) for the inclusive B ̄ → Xsγγ process, where the kinematical variables s1 and s2 are defined as si = (pb − qi)2=m2b with pb, q1, q2 being the momenta of the b-quark and two photons. This calculation completes the next-to-leading- logarithmic (NLL) QCD prediction of the numerically important self-interference contribution of O7 by keeping the full dependence on the strange-quark mass ms, which is introduced to control possible collinear configurations of one of the photons with the strange quark. Our results are given for exact ms, in contrast to an earlier work where only logarithmic and constant terms in ms were retained. This improved NLL result for the (O7; O7)-interference contribution shows that finite ms effects are only sizable near the kinematical endpoints of the spectrum dΓ=(ds1ds2). At the level of the branching ratio, in the phase-space region considered in this paper, it is observed that Br1[B ̄→ Xsγγ] does not develop a sizable ms dependence: the impact on this branching ratio is less than 5% when ms is varied between 400–600 MeV. For the same phase-space region finite strange quark mass effects for the branching ratio are less than 7%.

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