84 research outputs found
Unstable particles in matter at a finite temperature: the rho and omega mesons
Unstable particles (such as the vector mesons) have an important role to play
in low mass dilepton production resulting from heavy ion collisions and this
has been a subject of several investigations. Yet subtleties, such as the
implications of the generalization of the Breit-Wigner formula for nonzero
temperature and density, e.g. the question of collisional broadening, the role
of Bose enhancement, etc., the possibility of the kinematic opening (or
closing) of decay channels due to environmental effects, the problem of double
counting through resonant and direct contributions, are often given
insufficient emphasis. The present study attempts to point out these features
using the rho and omega mesons as illustrative examples. The difference between
the two versions of the Vector Meson Dominance Model in the present context is
also presented. Effects of non-zero temperature and density, through vector
meson masses and decay widths, on dilepton spectra are studied, for
concreteness within the framework of a Walecka-type model, though most of the
basic issues highlighted apply to other scenarios as well.Comment: text and figures modifie
Microscopic theories of neutrino-^{12}C reactions
In view of the recent experiments on neutrino oscillations performed by the
LSND and KARMEN collaborations as well as of future experiments, we present new
theoretical results of the flux averaged and
cross sections. The approaches used are
charge-exchange RPA, charge-exchange RPA among quasi-particles (QRPA) and the
Shell Model. With a large-scale shell model calculation the exclusive cross
sections are in nice agreement with the experimental values for both reactions.
The inclusive cross section for coming from the decay-in-flight of
is to be compared to the experimental value
of , while the one due to
coming from the decay-at-rest of is which
agrees within experimental error bars with the measured values. The shell model
prediction for the decay-in-flight neutrino cross section is reduced compared
to the RPA one. This is mainly due to the different kind of correlations taken
into account in the calculation of the spin modes and partially due to the
shell-model configuration basis which is not large enough, as we show using
arguments based on sum-rules.Comment: 17 pages, latex, 5 figure
eta-prime Meson Production in Nucleon-Nucleon Collisions Near The Threshold
The production of mesons in the reactions and at threshold-near energies is analyzed within a covariant effective
meson-nucleon theory. The description of cross section and angular
distributions of the available data in this kinematical region in the
channel is accomplished by including meson currents and nucleon currents with
the resonances , and . Predictions
for the channel are given. The di-electron production from subsequent
Dalitz decay is also
calculated and numerical results are presented for intermediate energy and
kinematics of possible experiments with HADES, CLAS and KEK-PS
Dispersion of single-walled carbon nanotubes in alcohol-cholic acid mixtures
A procedure for dispersing single-walled carbon nanotubes (SWNTs) for the preparation of suspensions with high concentrations of individual nanotubes in various solvents was described. The most stable suspensions were obtained from a mixture of ethanol with cholic acid at an acid concentration of 0.018 mol/kg
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