6,480 research outputs found
Spin Alignment of Heavy Meson Revisited
Using heavy quark effective theory a factorized form for inclusive production
rate of a heavy meson can be obtained, in which the nonperturbative effect
related to the heavy meson can be characterized by matrix elements defined in
the heavy quark effective theory. Using this factorization, predictions for the
full spin density matrix of a spin-1 and spin-2 meson can be obtained and they
are characterized only by one coefficient representing the nonperturbative
effect. Predictions for spin-1 heavy meson are compared with experiment
performed at colliders in the energy range from GeV to
GeV, a complete agreement is found for - and -meson.
There are distinct differences from the existing approach and they are
discussed.Comment: 6 pages, Talk given at 3rd Circum-Pan-Pacific Symposium on "High
Energy Spin Physics", Beijing, China, 8-13, 200
Fragmentation Function and Nucleon Transversity Distribution in a Diquark Model
Based on a simple quark-diquark model, we propose a set of unpolarized,
longitudinally polarized and transversely polarized fragmentation functions for
the by fitting the unpolarized production data in annihilation. It is found that the helicity structure of the obtained
fragmentation functions is supported by the all available
experimental data on the longitudinal polarization. Within the same
framework of the diquark model, the nucleon transversity distributions are
presented and consistent descriptions of the available HERMES data on the
azimuthal spin asymmetries in pion electroproduction are obtained. Furthermore,
the spin transfers to the transversely polarized in the charged
lepton DIS on a transversely polarized nucleon target are predicted for future
experiments.Comment: Talk given in a seminar of U. Santa Mari
Revisiting spin alignment of heavy mesons in its inclusive production
In the heavy quark limit inclusive production rate of a heavy meson can be
factorized, in which the nonperturbative effect related to the heavy meson can
be characterized by matrix elements defined in the heavy quark effective
theory. Using this factorization, predictions for the full spin density matrix
of a spin-1 and spin-2 meson can be obtained and they are characterized only by
one coefficient representing the nonperturbative effect. Predictions for spin-1
heavy meson are compared with experiment performed at colliders in the
energy range from GeV to GeV, a complete agreement
is found for - and -meson. For meson, our prediction suffers
a large correction, as indicated by experimental data. There exists another
approach by taking heavy mesons as bound systems, in which the total angular
momentum of the light degrees of freedom is 1/2 and 3/2 for spin-1 and spin-2
meson respectively, then the diagonal parts of spin density matrices can be
obtained. However, there are distinct differences in the predictions from the
two approaches and they are discussed in detail.Comment: 14 pages with one figur
A4-based tri-bimaximal mixing within inverse and linear seesaw schemes
We consider tri-bimaximal lepton mixing within low-scale seesaw schemes where
light neutrino masses arise from TeV scale physics, potentially accessible at
the Large Hadron Collider (LHC). Two examples are considered, based on the A4
flavor symmetry realized within the inverse or the linear seesaw mechanisms.
Both are highly predictive so that in both the light neutrino sector
effectively depends only on three mass parameters and one Majorana phase, with
no CP violation in neutrino oscillations. We find that the linear seesaw leads
to a lower bound for neutrinoless double beta decay while the inverse seesaw
does not. The models also lead to potentially sizeable decay rates for lepton
flavor violating processes, tightly related by the assumed flavor symmetry.Comment: 8 pages, 3 figures. Experimental references added and figure 1
update
Spin alignment of vector meson in e+e- annihilation at Z0 pole
We calculate the spin density matrix of the vector meson produced in e+e-
annihilation at Z^0 pole. We show that the data imply a significant
polarization for the antiquark which is created in the fragmentation process of
the polarized initial quark and combines with the fragmenting quark to form the
vector meson. The direction of polarization is opposite to that of the
fragmenting quark and the magnitude is of the order of 0.5. A qualitative
explanation of this result based on the LUND string fragmentation model is
given.Comment: 15 pages, 2 fgiures; submitted to Phys. Rev.
Weakly correlated electrons on a square lattice: a renormalization group theory
We study the weakly interacting Hubbard model on the square lattice using a
one-loop renormalization group approach. The transition temperature T_c between
the metallic and (nearly) ordered states is found. In the parquet regime, (T_c
>> |mu|), the dominant correlations at temperatures below T_c are
antiferromagnetic while in the BCS regime (T_c << |mu|) at T_c the d-wave
singlet pairing susceptibility is most divergent.Comment: 12 pages, REVTEX, 3 figures included, submitted to Phys. Rev. Let
Higgs Decays in the Low Scale Type I See-Saw Model
The couplings of the low scale type I see-saw model are severely constrained
by the requirement of reproducing the correct neutrino mass and mixing
parameters, by the non-observation of lepton number and charged lepton flavour
violating processes and by electroweak precision data. We show that all these
constraints still allow for the possibility of an exotic Higgs decay channel
into a light neutrino and a heavy neutrino with a sizable branching ratio. We
also estimate the prospects to observe this decay at the LHC and discuss its
complementarity to the indirect probes of the low scale type I see-saw model
from experiments searching for the decay.Comment: 15 pages, 8 figures; references added and results unchanged; matched
with the published version on PL
Asymmetric Quark/Antiquark Hadronization in e+e- Annihilation
We point out that the fragmentation of a strange quark into nucleons versus
antinucleons is not necessarily identical , even though the perturbative contributions from gluon splitting
and evolution are symmetric. The observation of such
asymmetries in the hadronization of strange and other heavy quarks can provide
insight into the nonperturbative mechanisms underlying jet fragmentation in
QCD.Comment: Latex, 12 page
Statistical approach for unpolarized fragmentation functions for the octet baryons
A statistical model for the parton distributions in the nucleon has proven
its efficiency in the analysis of deep inelastic scattering data, so we propose
to extend this approach to the description of unpolarized fragmentation
functions for the octet baryons. The characteristics of the model are
determined by using some data on the inclusive production of proton and
in unpolarized deep inelastic scattering and a next-to-leading
analysis of the available experimental data on the production of unpolarized
octet baryons in annihilation. Our results show that both parton
distributions and fragmentation functions are compatible with the statistical
approach, in terms of a few free parameters, whose interpretation will be
discussed.Comment: 14 pages, 7 eps figures, to appear in Phys. Rev.
Quark deconfinement phase transition in nuclear matter for improved quark mass density-dependent model
The improved quark mass density-dependent (IQMDD) model, which has been
successfully used to describe the properties of both infinite nuclear matter
and finite nuclei, is applied to investigate the properties of quark
deconfinement phase transition. By using the finite-temperature quantum field
theory, we calculate the finite temperature effective potential and extend the
IQMDD model to finite temperature and finite nuclear matter density. The
critical temperature and the critical density of nuclear matter are given and
the QCD phase diagram is addressed. It is shown that this model can not only
describe the saturation properties of nuclear matter, but also explain the
quark deconfinement phase transition successfully
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