1,002 research outputs found
The endpoint region in radiative quarkonia decays
We consider the inclusive radiative decays quarkonium -> gamma + hadrons and
examine the effects of soft QCD radiation on the photon energy spectrum near
the endpoint.Comment: Presented at the DPF2000 Meeting, Ohio State University, August 2000.
(Version 2: minor typos corrected.
Role of "Intrinsic Charm" in Semi-Leptonic B-Meson Decays
We discuss the role of so-called "intrinsic-charm" operators in semi-leptonic
B-meson decays, which appear first at order 1/m_b^3 in the heavy quark
expansion. We show by explicit calculation that -- at scales mu <= m_c -- the
contributions from "intrinsic-charm" effects can be absorbed into
short-distance coefficient functions multiplying, for instance, the Darwin
term. Then, the only remnant of "intrinsic charm" are logarithms of the form
ln(m_c^2/m_b^2), which can be resummed by using renormalization-group
techniques. As long as the dynamics at the charm-quark scale is perturbative,
alpha_s(m_c) << 1, this implies that no additional non-perturbative matrix
elements aside from the Darwin and the spin-orbit term have to be introduced at
order 1/m_b^3. Hence, no sources for additional hadronic uncertainties have to
be taken into account. Similar arguments may be made for higher orders in the
1/m_b expansion.Comment: 14 pages, 1 figure, uses slashed.sty, slight modifications to match
published versio
Enhanced electroweak penguin amplitude in B-->VV decays
We discuss a novel electromagnetic penguin contribution to the transverse
helicity amplitudes in B decays to two vector mesons, which is enhanced by two
powers of mB/Lambda relative to the standard penguin amplitudes. This leads to
unique polarization signatures in penguin-dominated decay modes such as B-->rho
K* similar to polarization effects in the radiative decay B-->K*gamma, and
offers new opportunities to probe the magnitude and chirality of
flavour-changing neutral current couplings to photons.Comment: 4 pages, 1 figur
Non-perturbative effects in semi-leptonic B_c decays
We discuss the impact of the soft degrees of freedom inside the B_c meson on
its rate in the semi-leptonic decay B_c -> X l nu_l where X denotes light
hadrons below the D^0 threshold. In particular we identify contributions
involving soft hadrons which are non-vanishing in the limit of massless
leptons. These contributions become relevant for a measurement of the purely
leptonic B_c decay rate, which due to helicity suppression involves a factor
m_l^2 and thus is much smaller than the contributions involving soft hadrons.Comment: LaTeX, 22 pages, 1 figur
The Renormalization Group Evolution of the CKM Matrix
We compute the renormalization of the complete CKM matrix in the MSbar scheme
and perform a renormalization group analysis of the CKM parameters. The
calculation is simplified by studying only the Higgs sector, which for the
\beta-function of the CKM matrix is at one loop the same as in the full
Standard Model. The renormalization group flow including QCD corrections can be
computed analytically using the hierarchy of the CKM parameters and the large
mass differences between the quarks. While the evolution of the Cabibbo angle
is tiny V_{ub} and V_{cb} increase sizably. We compare our results with the
ones in the full Standard Model.Comment: Latex, 31 pages, extensions amsmath, epsfig required The complete
paper, including figures, is also available via anonymous ftp at
ftp://ttpux2.physik.uni-karlsruhe.de/, or via www at
http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints
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