712 research outputs found
Photon Energy Spectrum in and Comparison with Data
A comparison of the inclusive photon energy spectrum in the radiative decay
\BGAMAXS, measured recently by the CLEO collaboration, with the standard
model is presented, using a -meson wave function model and improving earlier
perturbative QCD-based computations of the same. The dependence of the photon
energy spectrum on the non-perturbative model parameters, , the -quark
Fermi momentum in the hadron, and , the spectator quark mass, is
explicitly shown, allowing a comparison of these parameters with the ones
obtained from the analysis of the lepton energy spectrum in semileptonic
decays. Taking into account present uncertainties, we estimate \BBGAMAXS =
(2.55 \pm 1.28) \times 10^{-4} in the standard model, assuming
\absvts/\absvcb= 1.0. Comparing this with the CLEO measurement \BBGAMAXS =
(2.32 \pm 0.67) \times 10^{-4} implies \absvts/\absvcb= 1.1 \pm 0.43, in
agreement with the CKM unitarity.Comment: 16 pages (including 5 Figures as encapsulated ps-files: use epsf and
rotate
Tree-level contribution to \bar{B} -> X_d gamma using fragmentation functions
We evaluate the most important tree-level contributions connected with the
b-> u \bar{u} d gamma transition to the inclusive radiative decay \bar{B}-> X_d
gamma using fragmentation functions. In this framework the singularities
arising from collinear photon emission from the light quarks (u, \bar{u} and d)
can be absorbed into the (bare) quark-to-photon fragmentation function. We use
as input the fragmentation function extracted by the ALEPH group from the
two-jet cross section measured at LEP, where one of the jets is required to
contain a photon. To get the quark-to-photon fragmentation function at the
fragmentation scale \mu_F \sim m_b, we use the evolution equation, which we
solve numerically. We then calculate the (integrated) photon energy spectrum
for b-> u \bar{u} d gamma related to the operators P^u_{1,2}. For comparison,
we also give the corresponding results when using nonzero (constituent) masses
for the light quarks.Comment: 13 pages, 4 figure
Indirect search for supersymmetry in rare B decays
QCD corrections to the gluino induced contribution to b --> s gamma are shown
to be important in order to extract reliable bounds on the off-diagonal
elements of the squark mass matrices.Comment: 4 pages including 2 postscript figure
Inclusive Decay Rate for in Next-to-Leading Logarithmic Order and CP Asymmetry in the Standard Model
We compute the decay rate for the CKM-suppressed electromagnetic penguin
decay (and its charge conjugate) in NLO QCD, including
leading power corrections in and in the standard model. The
average branching ratio of the decay and its charge conjugate
is estimated to be in the range , obtained by varying the CKM-Wolfenstein parameters
and in the range and and taking into account other parametric dependence. In the stated
range of the CKM parameters, we find the ratio to lie in the range between 0.017 and 0.074.
Theoretical uncertainties in this ratio are found to be small. Hence, this
ratio is well suited to provide independent constraints on the CKM parameters.
The CP-asymmetry in the decay rates is found to be in the
range . Both the decay rates and CP asymmetry are measurable in
forthcoming experiments at factories and possibly at HERA-B.Comment: 17 pages including 7 postscript figures; uses epsfig; The changes
w.r.t the previous version are: A comment about the Bremsstrahlung
corrections is added as well as a note on the feasibility of the measurement
$B -> X_d gamma
Contribution of through the QCD anomaly in exclusive decays and
We compute the decay rates for the exclusive decays and in a QCD-improved factorization framework by including the
contribution from the process through
the QCD anomaly. This method provides an alternative estimate of the
contribution to these decays as
compared to the one using the intrinsic charm content of the
and mesons determined through the decays . The resulting branching ratios are compared with the CLEO
data on and
and predictions are made for the rest.Comment: 16 pages including 4 postscript figures; uses epsfig. The most recent
branching ratios from CLEO, ref. [5], are taken into account. The theory part
is unchange
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