Quark mass effects in anti-B ---> X(s gamma)

Apr, 2001
28 pages
Published in:
  • Nucl.Phys.B 611 (2001) 338-366
e-Print:
Report number:
  • CERN-TH-2001-089,
  • IFT-11-2001

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Abstract: (Elsevier)
The charm-loop contribution to B ̄ →X s γ is found to be numerically dominant and very stable under logarithmic QCD corrections. The strong enhancement of the branching ratio by QCD logarithms is mainly due to the b -quark mass evolution in the top-quark sector. These observations allow us to achieve better control over residual scale-dependence at the next-to-leading order. Furthermore, we observe that the sensitivity of the matrix element 〈X s γ|( s ̄ c) V−A ( c ̄ b) V−A |b〉 to m c / m b is the source of a sizeable uncertainty that has not been properly taken into account in previous analyses. Replacing m c pole / m b pole in this matrix element by the more appropriate m c MS (μ)/m b pole with μ ∈[ m c , m b ] causes an 11% enhancement of the SM prediction for BR [ B ̄ →X s γ] . For E γ >1.6 GeV in the B̄ -meson rest frame, we find BR [ B ̄ →X s γ] E γ >1.6  GeV =(3.60±0.30)×10 −4 . The difference between our result and the current experimental world average is consistent with zero at the level of 1.6 σ . We also discuss the implementation of new physics effects in our calculation. The Two-Higgs-Doublet-Model II with a charged Higgs boson lighter than 450 GeV is found to be strongly disfavoured.
Note:
  • Nucl. Phys. B 611 (2001) 338. Comparison with experiment is updated in the present hep-ph version. In particular, the published results of CLEO (hep-ex/0108032) are taken into account. 30 pages, 6 figures, uses graphicx
  • 12.60.Fr
  • 13.20.He
  • anti-B: radiative decay
  • decay: inclusive reaction
  • strangeness
  • quantum chromodynamics: correction
  • Feynman graph: higher-order
  • quark: mass
  • bottom
  • anti-B: branching ratio
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