478 research outputs found
Flavor-Singlet B-Decay Amplitudes in QCD Factorization
Exclusive hadronic B-meson decays into two-body final states consisting of a
light pseudoscalar or vector meson along with an eta or eta' meson are of great
phenomenological interest. Their theoretical analysis involves decay mechanisms
that are unique to flavor-singlet states, such as their coupling to gluons or
their ``intrinsic charm'' content. These issues are studied systematically in
the context of QCD factorization and the heavy-quark expansion. Theory can
account for the experimental data on the B->K^{(*)} eta^{(')} branching
fractions, albeit within large uncertainties.Comment: 25 pages, 5 figure
QCD factorization for B->PP and B->PV decays
A comprehensive study of exclusive hadronic B-meson decays into final states
containing two pseudoscalar mesons (PP) or a pseudoscalar and a vector meson
(PV) is presented. The decay amplitudes are calculated at leading power in
Lambda_{QCD}/m_b and at next-to-leading order in alpha_s using the QCD
factorization approach. The calculation of the relevant hard-scattering kernels
is completed. Important classes of power corrections, including
``chirally-enhanced'' terms and weak annihilation contributions, are estimated
and included in the phenomenological analysis. Predictions are presented for
the branching ratios of the complete set of the 96 decays of B^-, B^0, and B_s
mesons into PP and PV final states, and for most of the corresponding CP
asymmetries. Several decays and observables of particular phenomenological
interest are discussed in detail, including the magnitudes of the penguin
amplitudes in PP and PV final states, an analysis of the pi-rho system, and the
time-dependent CP asymmetry in the K phi and K eta' final states.Comment: 92 pages, 13 figures, 28 tables; typos and errors in data tables
corrected; version to appear in Nuclear Physics
alpha_s and the tau hadronic width: fixed-order, contour-improved and higher-order perturbation theory
The determination of from hadronic decays is revisited,
with a special emphasis on the question of higher-order perturbative
corrections and different possibilities of resumming the perturbative series
with the renormalisation group: fixed-order (FOPT) vs. contour-improved
perturbation theory (CIPT). The difference between these approaches has evolved
into a systematic effect that does not go away as higher orders in the
perturbative expansion are added. We attempt to clarify under which
circumstances one or the other approach provides a better approximation to the
true result. To this end, we propose to describe the Adler function series by a
model that includes the exactly known coefficients and theoretical constraints
on the large-order behaviour originating from the operator product expansion
and the renormalisation group. Within this framework we find that while CIPT is
unable to account for the fully resummed series, FOPT smoothly approaches the
Borel sum, before the expected divergent behaviour sets in at even higher
orders. Employing FOPT up to the fifth order to determine in the
\MSb scheme, we obtain ,
corresponding to . Improving
this result by including yet higher orders from our model yields
, which after evolution leads to
. Our results are lower than previous values
obtained from decays.Comment: 42 pages, 9 figures; appendix on Adler function in the complex plane
added. Version to appear in JHE
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