The
c →
uγ transition does not occur at the tree level in the Standard Model and is strongly GIM-suppressed at one loop. The leading QCD logarithms are known to enhance the amplitude by two orders of ...magnitude. We point out that the amplitude increases further by two orders of magnitude after including the complete 2-loop QCD contributions. Nevertheless,
ΔS = 0 radiative decays of charmed hadrons remain dominated by the
c → d
duγ
and
c → s
suγ
quark subprocesses.
We compute the
O
(
α
s
2
)
contributions to the photon energy spectrum of the inclusive decay
B
¯
→
X
s
γ
associated with the magnetic penguin operator
O
7
. They are an essential part of the ongoing ...NNLO calculation of this important decay. We use two different methods to evaluate the master integrals, one based on the differential equation approach and the other on sector decomposition, leading to identical results which in turn agree with those of a recent independent calculation by Melnikov and Mitov. We study the numerical relevance of this set of NNLO contributions in the photon energy spectrum and discuss the change of bottom quark mass scheme.
AbstractWe review the NLL QCD calculations for the branching ratio of B → Xsγ in the SM. In particular, we emphasize the problem related to the definition of the charm quark mass which leads to a ...rather large uncertainty of the NLL predictions. The various steps needed for a NNLL calculation, in which the mc issue can be settled, is also sketched. We briefly summarize the results of a calculation of the \({\cal O} (\alpha_s^2 n_f)\) corrections to BR(B → Xsγ), which was recently performed as a first step in the NNLL program. We then also briefly review the status of the photon energy spectrum and show the comparison with experimental data. Finally, we review the status of the CKM suppressed decay mode B → Xdγ.
JHEP 1701 (2017) 084 We present the differential decay rates and the branching ratios of the muon
decay with internal conversion, $\mu \to e \, (e^+e^-) \, \nu \bar{\nu}$, in
the Standard Model at ...next-to-leading order (NLO) in the on-shell scheme. This
rare decay mode of the muon is among the main sources of background to the
search for $\mu \to eee$ decay. We found that in the phase space region where
the neutrino energies are small, and the three-electron momenta have a similar
signature as in the $\mu \to eee$ decay, the NLO corrections decrease the
leading-order prediction by about $10-20\%$
We calculate
CP-violating rate asymmetries in the rare radiative decays
B
± → K
∗±γ
and
B
± →
ϱ
±
γ. They arise because of the interference between leading-order penguin amplitudes and one-gluon ...corrections with absorptive phases, and provide unambiguous evidence for direct
CP violation. Complementing earlier studies, we also investigate gluon exchange with the ‘spectator’ quark. The bound state effects in the exclusive matrix elements are taken into account by a covariant model, which yields a branching ratio
BR(B → K
∗γ) = (4 − 5) × 10
−5
in good agreement with the observed value. The bound state effects increase the
CP asymmetry, which is of order 1% in the channel
B → K
∗γ
and 15% for
B →
ϱγ.
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