7 It is very small (0.2% for charged leptons, 0.8% for u-type quarks and 0.02% for d-type quarks). δ$_{QCD}$ gives the QCD corrections common to all quarks and it is given by α$_{s}$ is the QCD coupling constant taken at the m$_{Z}$ scale, i.e. α$_{s}$ = α$_{s}$ ( m 2 $_{Z}$) = 0 . 12. δ q µ contains the kinematical effects of the external fermion masses, including some mass- dependent QCD radiative corrections. It is only important for the b-quark (0.5%) and to a lesser extent for the τ -lepton (0.2%) and the c-quark (0.05%). It is given by By taking appropriate branching ratios it is possible to isolate the large top mass depen- dent Zb ¯ b vertex δ$_{b}$ [51], where µ 2 q ≡ 4 ¯ m 2 $_{q}$( m 2 $_{Z}$) /m 2 $_{Z}$. where R$_{q}$ ≡ Γ( $^{Z}$→b ¯ b ) Γ( $^{Z}$→q ¯ q $_{)}$. All other corrections cancel exactly in this branching ratio except the correction to the Zb ¯ b vertex which only depends on the top quark mass. Radiative B decays have been a topic of great theoretical and experimental interest for long. Although the inclusive radiative decay B → X$_{s}$γ is loop suppressed within the SM, it has relatively large branching ratio making it statistically favorable from the experimental point of view and hence it serves as an important probe to test SM and its possible extensions. The present world average of Br ( B → X$_{s}$γ ) is (3 . 55 ± 0 . 25) × 10 − 4 [52] which is in good agreement with its SM prediction [53, 54]. Apart from the branching ratio of B → X$_{s}$γ , direct CP violation in B → X$_{s}$γ , A $^{B}$→X$_{s}$γ CP , can serve as an important observable to search physics beyond SM; therefore we will also study this direct CP asymmetry in this paper (see Section III A). C. B → X$_{s}$γ decay R$_{h}$ ≡ Γ( Z → b ¯ ) Γ( Z → hadrons ) = ( 1 + 2 /R$_{s}$ + 1 /R$_{c}$ + 1 /R$_{u}$ ) − $^{1}$, (12) ¯ δ q µ = 3 µ 2 q v 2 q + a 2 q ( − 1 2 a 2 q ( 1 + 8 α$_{s}$ 3 π ) + v 2 q α$_{s}$ π ) , (11) δ$_{QCD}$ = α$_{s}$ π + 1 . 41 ( α$_{s}$ π ) $^{2}$. (10)