117 research outputs found
Final state interaction effects in neutrino-nucleus quasielastic scattering
We consider the charged-current quasielastic scattering of muon neutrinos on
an Oxygen 16 target, described within a relativistic shell model and, for
comparison, the relativistic Fermi gas. Final state interactions are described
in the distorted wave impulse approximation, using both a relativistic mean
field potential and a relativistic optical potential, with and without
imaginary part. We present results for inclusive cross sections at fixed
neutrino energies in the range 200 MeV - 1 GeV, showing that final
state interaction effects can remain sizable even at large energies.Comment: 4 pages, 4 figures; poster session of the Third International
Workshop on Neutrino-Nucleus Interactions in the Few GeV Region (NuInt04),
Gran Sasso (Italy), March 17-21, 2004; to appear in the proceeding
Spin-orbit correlation energy in neutron matter
We study the relevance of the energy correlation produced by the two-body
spin-orbit coupling present in realistic nucleon-nucleon potentials. To this
purpose, the neutron matter Equation of State (EoS) is calculated with the
realistic two-body Argonne potential. The shift occuring in the EoS when
spin-orbit terms are removed is taken as an estimate of the spin-orbit
correlation energy. Results obtained within the Bethe-Brueckner-Goldstone
expansion, extended up to three hole-line diagrams, are compared with other
many-body calculations recently presented in the literature. In particular,
excellent agreement is found with the Green's function Monte-Carlo method. This
agreement indicates the present theoretical accuracy in the calculation of the
neutron matter EoS.Comment: 5 pages, 2 figures, 2 tables; to appear in Phys. Rev.
Lepton mass effects in the Bethe-Heitler process
We develop the full finite lepton mass formalism for the production of real
photons via the Bethe-Heitler reaction of unpolarized leptons off unpolarized
nucleons. Genuine lepton mass effects are described, in particular their
dependence upon the lepton mass and the initial beam energy, as well as their
sensitivity to the nucleon isospin. In the minimum momentum transfer region,
these effects dominate the muon induced proton cross section and become
significant for electron scattering at small .Comment: Final version including errat
Neutron matter at low density and the unitary limit
Neutron matter at low density is studied within the hole-line expansion.
Calculations are performed in the range of Fermi momentum between 0.4 and
0.8 fm. It is found that the Equation of State is determined by the
channel only, the three-body forces contribution is quite small, the
effect of the single particle potential is negligible and the three hole-line
contribution is below 5% of the total energy and indeed vanishing small at the
lowest densities. Despite the unitary limit is actually never reached, the
total energy stays very close to one half of the free gas value throughout the
considered density range. A rank one separable representation of the bare NN
interaction, which reproduces the physical scattering length and effective
range, gives results almost indistinguishable from the full Brueckner G-matrix
calculations with a realistic force. The extension of the calculations below
fm does not indicate any pathological behavior of the
neutron Equation of State.Comment: 17 pages, 7 figures. To be published in Phys. Rev.
Looking for strangeness with neutrino-nucleon scattering
The possibility to determine the axial strange form factor of the nucleon
from elastic neutrino-nucleon scattering experiments is studied. The existing
experimental information is shortly mentioned and several observables which
could be measured in the near future at new neutrino facilities are discussed.Comment: 6 pages, 1 figure, contribution to : "NuFact 03", 5th International
Workshop on Neutrino Factories & Superbeams, Columbia University, New York,
5-11 June 200
Local Fermi gas in inclusive muon capture from nuclei
We compare local Fermi gas and shell model in muon capture in nuclei in order
to estimate the effect of finite nuclear size in low energy weak reactions.Comment: 6 pages, 8 figures. To be published in the Proceedings of 20th Max
Born Symposium, Wroclaw (Poland), December 7-10, 200
Evolution of the pygmy dipole resonance in nuclei with neutron excess
The electric dipole excitation of various nuclei is calculated with a Random
Phase Approximation phenomenological approach. The evolution of the strength
distribution in various groups of isotopes, oxygen, calcium, zirconium and tin,
is studied. The neutron excess produces strength in the low energy region.
Indexes to measure the collectivity of the excitation are defined. We studied
the behavior of proton and neutron transition densities to determine the
isoscalar or isovector nature of the excitation. We observed that in
medium-heavy nuclei the low-energy excitation has characteristics rather
different that those exhibited by the giant dipole resonance. This new type of
excitation can be identified as pygmy dipole resonance.Comment: 14 pages, 12 figures, 7 table
Evolution of the pygmy dipole resonance in nuclei with neutron excess
The electric dipole excitation of various nuclei is calculated with a Random
Phase Approximation phenomenological approach. The evolution of the strength
distribution in various groups of isotopes, oxygen, calcium, zirconium and tin,
is studied. The neutron excess produces strength in the low energy region.
Indexes to measure the collectivity of the excitation are defined. We studied
the behavior of proton and neutron transition densities to determine the
isoscalar or isovector nature of the excitation. We observed that in
medium-heavy nuclei the low-energy excitation has characteristics rather
different that those exhibited by the giant dipole resonance. This new type of
excitation can be identified as pygmy dipole resonance.Comment: 14 pages, 12 figures, 7 table
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