Weak radiative decays of the B mesons belong to the most important flavor changing processes that provide constraints on physics at the TeV scale. In the derivation of such constraints, accurate ...standard model predictions for the inclusive branching ratios play a crucial role. In the current Letter we present an update of these predictions, incorporating all our results for the O(α_{s}^{2}) and lower-order perturbative corrections that have been calculated after 2006. New estimates of nonperturbative effects are taken into account, too. For the CP- and isospin-averaged branching ratios, we find B_{sγ}=(3.36±0.23)×10^{-4} and B_{dγ}=(1.73_{-0.22}^{+0.12})×10^{-5}, for E_{γ}>1.6 GeV. Both results remain in agreement with the current experimental averages. Normalizing their sum to the inclusive semileptonic branching ratio, we obtain R_{γ}≡(B_{sγ}+B_{dγ})/B_{cℓν}=(3.31±0.22)×10^{-3}. A new bound from B_{sγ} on the charged Higgs boson mass in the two-Higgs-doublet-model II reads M_{H^{±}}>480 GeV at 95% C.L.
The 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/mb2 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 BrB¯→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%.
Towards B→Vγ decays at NNLO in SCET Ali, A.; Pecjak, B.D.; Greub, C.
The European physical journal. C, Particles and fields,
06/2008, Letnik:
55, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We compute NNLO (
(α
s
2
)) corrections to the hard-scattering kernels entering the QCD factorization formula for B→Vγ decays, where V is a light vector meson. We give complete NNLO results for the ...dipole operators Q
7
and Q
8
, and partial results for Q
1
valid in the large-β
0
limit and neglecting the NNLO correction from hard-spectator scattering. Large perturbative logarithms in the hard-scattering kernels are identified and resummed using soft-collinear effective theory. We use our results to estimate the branching fractions for B→K
*
γ and B
s
→φγ decays at NNLO and compare them with the current experimental data.
We compute the QCD corrections to the decay rate difference in the
B
s
–
B
̄
s
system, Δ
Γ
B
s
, in the next-to-leading logarithmic approximation using the heavy quark expansion approach. Going ...beyond leading order in QCD is essential to obtain a proper matching of the Wilson coefficients to the matrix elements of local operators from lattice gauge theory. The lifetime difference is reduced considerably at next-to-leading order. We find
(
ΔΓ/Γ)
B
s
=(f
B
s
/210
MeV)
20.006B(m
b)+0.150B
S(m
b)−0.063
in terms of the bag parameters
B,
B
S
in the NDR scheme. As a further application of our analysis we also derive the next-to-leading order result for the mixing-induced CP asymmetry in inclusive
b→u
u
̄
d
decays, which measures sin2
α.
In this analysis, we present the contribution associated with the chromomagnetic dipole operator O sub(8) to the double differential decay width dGamma/(ds sub(1)ds sub(2)) for the inclusive process ...B arrow right X sub(s)g gamma . The kinematical variables s sub(1) and s sub(2) are defined as (ProQuest: Formulae and/or non-USASCII text omitted), where p sub(b) q sub(1), q sub(2) are the momenta of b quark and two photons. This contribution (taken at tree level) is of order alpha s, 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 m sub(s)for the strange quark. Our results are obtained for exact m sub(s) which we interpret as a constituent mass being varied between 400 and 600 MeV. Numerically it turns out that the effect of the (O sub(8), O sub(8)) contribution to the branching ratio of B arrow right X sub(s)g gamma 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 dGamma sub(77)/(ds sub(1)ds sub(2)).
In this Letter we present the analytic results for the two-loop corrections to the Wilson coefficients C9(μW) and C10(μW) in type-I and type-II two-Higgs-doublet models at the matching scale μW. ...These corrections are important ingredients for next-to-next-to-leading logarithmic predictions of various observables related to the decays B→Xsl+l− in these models. In scenarios with moderate values of tanβ neutral Higgs boson contributions can be safely neglected for l=e,μ. Therefore we concentrate on the contributions mediated by charged Higgs bosons.
PDF
