42,156 research outputs found
Study of semileptonic and nonleptonic decays of the meson
We evaluate semileptonic and two--meson nonleptonic decays of the
meson in the framework of a nonrelativistic quark model. The former are done in
spectator approximation using one--body current operators at the quark level.
Our model reproduces the constraints of heavy quark spin symmetry obtained in
the limit of infinite heavy quark mass. For the two--meson nonleptonic decays
we work in factorization approximation. We compare our results to the ones
obtained in different relativistic approaches.Comment: Talk given at the IVth International Conference on Quarks an Nuclear
Physics, Madrid, June 5th-10th 200
Electromagnetic radiation produced by avalanches in the magnetization reversal of Mn12-Acetate
Electromagnetic radiation produced by avalanches in the magnetization
reversal of Mn12-Acetate has been measured. Short bursts of radiation have been
detected, with intensity significantly exceeding the intensity of the
black-body radiation from the sample. The model based upon superradiance from
inversely populated spin levels has been suggested
Quantum dynamics of vortices in mesoscopic magnetic disks
Model of quantum depinning of magnetic vortex cores from line defects in a
disk geometry and under the application of an in-plane magnetic field has been
developed within the framework of the Caldeira-Leggett theory. The
corresponding instanton solutions are computed for several values of the
magnetic field. Expressions for the crossover temperature Tc and for the
depinning rate \Gamma(T) are obtained. Fitting of the theory parameters to
experimental data is also presented.Comment: 8 page
Quark model study of the semileptonic B -> pi decay
The semileptonic decay B->pi is studied starting from a simple quark model
and taking into account the effect of the B* resonance. A novel, multiply
subtracted, Omn\`es dispersion relation has been implemented to extend the
predictions of the quark model to all physical q^2 values. We find
|V_{ub}|=0.0034 +/- 0.0003(exp.)+/- 0.0007(theory), in good agreement with
experiment.Comment: Three pages, two figures. To appear in the proceedings of Quark
Confinament and Hadron Spectrum VII. Azores, September 200
Transverse parton momenta in single inclusive hadron production in annihilation processes
We study the transverse momentum distributions of single inclusive hadron
production in annihilation processes. Although the only
available experimental data are scarce and quite old, we find that the
fundamental features of transverse momentum dependent (TMD) evolution,
historically addressed in Drell-Yan processes and, more recently, in
Semi-inclusive deep inelastic scattering processes, are visible in annihilations as well. Interesting effects related to its non-perturbative
regime can be observed. We test two different parameterizations for the
dependence of the cross section: the usual Gaussian distribution and
a power-law model. We find the latter to be more appropriate in describing this
particular set of experimental data, over a relatively large range of
values. We use this model to map some of the features of the data within the
framework of TMD evolution, and discuss the caveats of this and other possible
interpretations, related to the one-dimensional nature of the available
experimental data
On the Jacobi-Metric Stability Criterion
We investigate the exact relation existing between the stability equation for
the solutions of a mechanical system and the geodesic deviation equation of the
associated geodesic problem in the Jacobi metric constructed via the
Maupertuis-Jacobi Principle. We conclude that the dynamical and geometrical
approaches to the stability/instability problem are not equivalent.Comment: 14 pages, no figure
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