9,636 research outputs found
Charming Penguins in B decays
Full expressions of the and
amplitudes, given in terms of matrix elements of operators of the effective
weak Hamiltonian, are used to study the dependence of the relevant branching
ratios on the different contributions. The uncertainty in the extraction of the
weak phase from the measurement of the time-dependent asymmetry in
decays is also analyzed. We find that, among several
effects which may enhance the branching ratio, the most
important is due to ``charming penguin" diagrams that have never been studied
before. These diagrams easily increase up to a
value of . The same effect produces, however, a large error
in the extraction of from the measurement of the time-dependent asymmetry. We show that it is possible to determine
charming-penguin amplitudes from the experimental measurement of many decay
rates. Their effect is impressive in and decays, where charming-penguin contributions easily give values of
and of about . Among other possibilities, we also suggest to use , the BR of which can be as large as , to determine the
size of charming-penguin amplitudes.Comment: LaTeX, 28 pages, 8 figure
NNLO Unquenched Calculation of the b Quark Mass
By combining the first unquenched lattice computation of the B-meson binding
energy and the two-loop contribution to the lattice HQET residual mass, we
determine the (\bar{{MS}}) (b)-quark mass, (\bar{m}_{b}(\bar{m}_{b})). The
inclusion of the two-loop corrections is essential to extract
(\bar{m}_{b}(\bar{m}_{b})) with a precision of ({\cal
O}(\Lambda^{2}_{QCD}/m_{b})), which is the uncertainty due to the renormalon
singularities in the perturbative series of the residual mass. Our best
estimate is (\bar{m}_{b}(\bar{m}_{b}) = (4.26 \pm 0.09) {\rm GeV}), where we
have combined the different errors in quadrature. A detailed discussion of the
systematic errors contributing to the final number is presented. Our results
have been obtained on a sample of (60) lattices of size (24^{3}\times 40) at
(\beta =5.6), using the Wilson action for light quarks and the lattice HQET for
the (b) quark, at two values of the sea quark masses. The quark propagators
have been computed using the unquenched links generated by the T(\chi)L
Collaboration.Comment: 19 pages, 1 figur
Scheme Independence of the Effective Hamiltonian for and Decays
We present a calculation of the effective weak Hamiltonian which governs and transitions in two different
renormalization schemes (NDR and HV). In the leading logarithmic approximation,
we show that the coefficients of the effective Hamiltonian are scheme
independent only when one takes correctly into account the scheme dependence of
one- and two- loop diagrams. We demonstrate that in NDR there are contributions
which were missed in previous calculations. These contributions are necessary
to obtain scheme independent coefficients in the final results.Comment: 16 pp + 5 figures not included (available by anonymous ftp at
amisan.iss.infn.it (141.108.15.215), directory /ftp/bsgamma), LaTeX, LPTENS
93/28, ROME 93/958, ULB-TH 93/0
Penguin Contractions and Factorization in B -> K pi Decays
We study Lambda_{QCD}/m_B corrections to factorization in B -> K pi decays.
First, we analyze these decay channels within factorization, showing that,
irrespectively of the value of gamma, it is not possible to reproduce the
experimental data. Then, we discuss Lambda_{QCD}/m_B corrections to these
processes, and argue that there is a class of doubly Cabibbo enhanced
non-factorizable contributions, usually called charming penguins, that cannot
be neglected. Including these corrections, we obtain an excellent agreement
with experimental data. Furthermore, contrary to what is obtained with
factorization, we predict sizable rate asymmetries in B^\pm -> K^\pm \pi^0 and
B -> K^\pm pi^\mp.Comment: 4 pages, 3 figures. Talk given by L. Silvestrini at BCP4, Ise-Shima,
Japan, 18-23 Feb 200
Model independent determination of the light-cone wave functions for exclusive processes
We present a method to compute, by numerical simulations of lattice QCD, the
light-cone wave functions which enter exclusive processes at large momentum
transfer, such as electromagnetic elastic scatterings, or exclusive
semi-leptonic decays as B -> pi (B -> rho) and radiative decays as B -> K*
gamma. The method is based on first principles and does not require any model
assumption.Comment: 7 pages, LaTeX fil
Charming Penguins Saga
We briefly recall the main formulae for computing the B -> K pi branching
ratios within the "charming penguin" approach, present an updated fit to the
data, and explain why we believe that, in general, these fits can hardly be
used to extract gamma.Comment: Invited talk at FPCP '02 given by M. Ciuchini, uses econfmacros.tex.
Final version with minor changes to appear in the proceeding
Two Body B Decays, Factorization and LambdaQCD/mb Corrections
By using the recent experimental measurements of B -> pi pi and B -> K pi
branching ratios, we find that the amplitudes computed at the leading order of
the LambdaQCD/mb expansion disagree with the observed BRs, even taking into
account the uncertainties of the input parameters. Beyond the leading order,
Charming and GIM penguins allow to reconcile the theoretical predictions with
the data. Because of these large effects, we conclude, however, that it is not
possible, with the present theoretical and experimental accuracy, to determine
the CP violation angle gamma from these decays. We compare our results with
those obtained with the parametrization of the chirally enhanced
non-perturbative contributions by BBNS. We also predict large asymmetries for
several of the particle--antiparticle BRs, in particular BR(B+ -> K+ pi0),
BR(Bd -> K+ pi-) and BR(Bd -> pi+ pi-).Comment: 14 pages 3 figures uses aippro
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