We compute the decay rate for the CKM-suppressed electromagnetic penguin
decay B→Xd+γ (and its charge conjugate) in NLO QCD, including
leading power corrections in 1/mb2 and 1/mc2 in the standard model. The
average branching ratio of the decay B→Xdγ and its charge conjugate
is estimated to be in the range 6.0×10−6≤≤2.6×10−5, obtained by varying the CKM-Wolfenstein parameters
ρ and η in the range −0.1≤ρ≤0.4 and 0.2≤η≤0.46 and taking into account other parametric dependence. In the stated
range of the CKM parameters, we find the ratio R(dγ/sγ)=<BR(B→Xdγ)>/ to lie in the range between 0.017 and 0.074.
Theoretical uncertainties in this ratio are found to be small. Hence, this
ratio is well suited to provide independent constraints on the CKM parameters.
The CP-asymmetry in the B→Xdγ decay rates is found to be in the
range (7−35). Both the decay rates and CP asymmetry are measurable in
forthcoming experiments at B factories and possibly at HERA-B.Comment: 17 pages including 7 postscript figures; uses epsfig; The changes
w.r.t the previous version are: A comment about the Bremsstrahlung
corrections is added as well as a note on the feasibility of the measurement
$B -> X_d gamma