866 research outputs found
Semileptonic and nonleptonic decays of Bc
Using our relativistic constituent quark model we present results on the
exclusive nonleptonic and semileptonic decays of the Bc-meson. The nonleptonic
decays are studied in the framework of the factorization approximation. We
calculate the branching ratios for a large set of exclusive nonleptonic and
semileptonic decays of the Bc-meson and compare our results with the results of
other models.Comment: 4 pages, proceeding of the talk given by Pietro Santorelli at IFAE
2006, Pavia, 19-21 Aprile 200
J/\psi dissociation cross sections in a relativistic quark model
We calculate the amplitudes and the cross sections of the charm dissociation
processes J/\psi \pi => D \bar D, D* \bar D, D \bar D*, D* \bar D* within a
relativistic constituent quark model. We consistently account for the
contributions coming from both the box and triangle diagrams that contribute to
the dissociation processes. The cross section is dominated by the D* \bar D and
D* \bar D* channels. When summing up the four channels we find a maximum total
cross section of about 2.3 mb at sqrt(s) \approx 4.1 GeV. We compare our
results to the results of other model calculations.Comment: 22 pages, 9 figures, typos corrected, this version will appear on
Phys. Rev.
Semileptonic decays of Bc mesons into charmonium states in a relativistic quark model
We use the framework of a relativistic constituent quark model to study the
semileptonic transitions of the Bc meson into CCbar charmonium states where
CCbar = etaC (1S0), J/psi (3S1), chiC0 (3P0), chiC1 (3P1), hc (1P1), chiC2
(3P2), psi (3D2). We compute the q^2-dependence of all relevant form factors
and give predictions for their semileptonic Bc decay modes including also their
tau-modes. We derive a formula for the polar angle distribution of the charged
lepton in the (l nu) c.m. frame and compute the partial helicity rates that
multiply the angular factors in the decay distribution. For the discovery
channel [B_c => J/psi (=> mu+ mu-) l nu] we compute the transverse/longitudinal
composition of the J/psi which can be determined by an angular analysis of the
decay J/psi => mu+ mu-. We compare our results with the results of other
calculations.Comment: 16 pages RevTex, this version will appear in Physical Review
A search for Z' in muon neutrino associated charm production
In many extensions of the Standard Model the presence of an extra neutral
boson, Z', is invoked. A precision study of weak neutral-current exchange
processes involving only second generation fermions is still missing. We
propose a search for Z' in muon neutrino associated charm production. This
process only involves Z' couplings with fermions from the second generation. An
experimental method is thoroughly described using an ideal detector. As an
application, the accuracy reachable with present and future experiments has
been estimated.Comment: 13 pages, 3 figures, late
Coleman-Weinberg SO(10) GUT theories as inflationary models
The flat-space limit of the one-loop effective potential for SO(10) GUT theories in spatially flat Friedmann-Robertson-Walker cosmologies is applied to study the dynamics of the early universe. The numerical integration of the corresponding field equations shows that, for such grand unified theories, a sufficiently long inflationary stage is achieved for suitable choices of the initial conditions. However, a severe fine tuning of these initial conditions is necessary to obtain a large e-fold number. In the direction with residual symmetry SU(4)_{PS} \otimes SU(2)_{L} \otimes SU(2)_{R}, one eventually finds parametric resonance for suitable choices of the free parameters of the classical potential. This phenomenon leads in turn to the end of inflation
Statistical Inspired Parton Distributions and the Violation of QPM Sum Rules
A quantum statistical parametrization of parton distributions has been
considered. In this framework, the exclusion Pauli principle connects the
violation of the Gottfried sum rule with the Ellis and Jaffe one, and implies a
defect in the Bjorken sum rule. However, in terms of standard parametrizations
of the polarized distributions a good description of the data is obtained once
a large gluon polarization is provided. Interestingly, in this description
there is no violation of the Bjorken sum rule.Comment: 10 pages, LateX + 15 figures, Talk given at ``Hadrons 96'' Workshop,
Novy Svet (CRIMEA), June 9-1
Semileptonic and rare B meson decays into a light pseudoscalar meson
In the framework of a QCD relativistic potential model we evaluate the form
factors describing the exclusive decays B => \pi l nu and B => K l+ l-. The
present calculation extends a previous analysis of B meson decays into light
vector mesons. We find results in agreement with the data, when available, and
with the theoretical constraints imposed by the Callan-Treiman relation and the
infinite heavy quark mass limit.Comment: 11 pages LaTeX + 2 figure
Semileptonic and Rare -meson transitions in a QCD relativistic potential model
Using a QCD relativistic potential model, previously applied to the
calculation of the heavy meson leptonic constants, we evaluate the form factors
governing the exclusive decays , and . In our approach the heavy meson is described as a
bound state, whose wave function is solution of the relativistic Salpeter
equation, with an instantaneous potential displaying Coulombic behaviour at
small distances and linear behaviour at large distances. The light vector meson
is described by using a vector current interpolating field, according to the
Vector Meson Dominance assumption. A Pauli-Villars regularized propagator is
assumed for the quarks not constituting the heavy meson. Our procedure allows
to avoid the description of the light meson in terms of wave function and
constituent quarks, and consequently the problem of boosting the light meson
wave function.
Assuming as an input the experimental results on , we
evaluate all the form factors describing the semileptonic and
rare transitions. The overall comparison with the data, whenever available, is
satisfactory.Comment: Latex, 19 pages, 3 figure
The semileptonic decay Lambda_b -> Lambda_c + tau(-) + antinu_tau in the covariant confined quark model
Recently there has been much interest in the tauonic semileptonic meson
decays B -> D + tau + nu_tau and B -> D* + tau + nu_tau where one has found
larger rates than what is predicted by the Standard Model. We analyze the
corresponding semileptonic baryon decays Lambda_b(0) -> Lambda_c(+) + tau(-) +
antinu_tau with particular emphasis on the lepton helicity flip and scalar
contributions which vanish for zero lepton masses. We calculate the total rate,
differential decay distributions, the longitudinal and transverse polarization
of the daughter baryon Lambda_c(+) and the tau-lepton, and the lepton-side
forward-backward asymmetries. The nonvanishing polarization of the daughter
baryon Lambda_c(+) leads to hadron-side asymmetries in e.g. the decay
Lambda_c(+) -> Lambda(0) + pi(+) and azimuthal correlations between the two
final state decay planes which we specify. We provide numerical results on
these observables using results of the covariant confined quark model. We find
large lepton mass effects in the q2-spectra and in the polarization
observables.Comment: 26 page
Four-quark structure of Zc(3900), Z(4430) and Xb(5568) states
We examine the four-quark structure of the recently discovered charged
, , and states. We calculate the widths of the
strong decays (, ,
), (), and
within a covariant quark model previously developed by us.
We find that the tetraquark-type current widely used in the literature for the
leads to a significant suppression of the and modes. Contrary to this a molecular-type current provides an
enhancement by a factor of 6-7 for the modes compared with the
, modes in agreement with recent
experimental data from the BESIII Collaboration. In case of the state
we test a sensitivity of the ratio of the
and decay rates to a choice of the size parameter
of the . Using upper constraint for the sum of
these two modes deduced from the LHCb Collaboration data we find that
varies from 4.64 to 4.08 when changes from 2.2 to 3.2 GeV.
Also we make the prediction for the decay rate.Comment: 14 page
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