(O8, O8) contribution to B¯ → Xsγγ at O(αs)

In this analysis, we present the contribution associated with the chromomagnetic dipole operator O8 to the double differential decay width dΓ/(ds1ds2) for the inclusive process B¯→Xsγγ. The kinematical variables s1 and s2 are defined as si=(pb−qi)2/m2b, where pb, q1, q2 are the momenta of b quark and two photons. This contribution (taken at tree level) is of order αs, like the recently calculated QCD corrections to the contribution of the operator O7. In order to regulate possible collinear singularities of one of the photons with the strange quark, we introduce a nonzero mass ms for the strange quark. Our results are obtained for exact ms, which we interpret as a constituent mass being varied between 400 and 600 MeV. Numerically it turns out that the effect of the (O8, O8) contribution to the branching ratio of B¯→Xsγγ does not exceed +0.1% for any kinematically allowed value of our physical cutoff parameter c, confirming the expected suppression of this contribution relative to the QCD corrections to dΓ77/(ds1ds2).