471 research outputs found
B semileptonic moments at NNLO
The calculation of the moments in inclusive B meson semileptonic decays is
upgraded to O(alphas^2). The first three moments of the lepton energy and
invariant hadronic mass distributions are computed for arbitrary cuts on the
lepton energy and in various renormalization schemes, finding in general small
deviations from the O(alphas^2 beta0) calculation. I also review the relation
between MSbar and kinetic heavy quark masses.Comment: 28 pages, 9 figure
Precision Electroweak Measurements Circa 2002
Present global fits to electroweak data are characterized by two results that
differ from Standard Model expectations by about 3 sigma, the NuTeV measurement
of sin^2theta_W and the FB b quark asymmetries measured at LEP. I review
possible SM and new physics explanations of these anomalies and the
implications for the indirect determination of the Higgs mass.Comment: 6 pages, 2 figures, talk at ICHEP, Amsterdam, 24-31 July 200
Complete electroweak matching for radiative B decays
We compute the complete two-loop O(alpha) Wilson coefficients relevant for
radiative decays of the B meson in the SM. This is a necessary step in the
calculation of the O(alpha alpha_s^n ln^n m_b/M_W) corrections and improves on
our previous analysis of electroweak effects in B -> X_s gamma. We describe in
detail several interesting technical aspects of the calculation and include all
dominant QED matrix elements. In our final result, we neglect only terms
originated from the unknown O(alpha alpha_s) evolution of the Wilson
coefficients and some suppressed two-loop matrix elements. Due to the
compensation among different effects, we find that non-trivial electroweak
corrections decrease the branching ratio by about 3.6% for a light Higgs boson,
very close to our previous result. The corresponding up-to-date SM prediction
for the branching ratio with E_gamma > 1.6 GeV is (3.61 +- 0.30) x 10^-4.Comment: 20 pages, 2 figures, uses amssymb.sty, amsmath.sty and feynarts.sty.
Minor change
Electroweak effects in radiative B decays
We compute the two-loop electroweak corrections to the radiative decays of
the B meson in the SM. Electroweak effects reduce the Wilson coefficient
C_7^eff(mw) by 2.6% for a light Higgs boson of about 100 GeV and are less
important for a heavier Higgs. The leading term of a heavy top expansion of our
result differs from the one obtained in the gaugeless approximation where only
top quark Yukawa couplings are considered: we discuss the origin of the
discrepancy and provide a criterion for the validity of the gaugeless
approximation. As a byproduct of the calculation we also obtain the O(alpha)
corrections to the Wilson coefficient of the four-fermion operator Q_2. A
careful analysis of the interplay between electroweak and QCD effects leads to
an overall 2% reduction of the total branching ratio for B -> X_s gamma due to
purely electroweak corrections. For a light Higgs boson, the up-to-date SM
prediction is BR_gamma=3.29 10^-4.Comment: 15 pages, 3 figure
Revisiting
We re-examine the determination of from in view
of recent experimental and theoretical progress, discussing the
parameterization of the form factors and studying the role played by the
unitarity constraints. Our fit to experimental and lattice results for gives and to .Comment: 19 pages, 2 figures; v2: BCL fits, various clarifications and refs
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