8,561 research outputs found
On the analytic solution of the pairing problem: one pair in many levels
We search for approximate, but analytic solutions of the pairing problem for
one pair of nucleons in many levels of a potential well. For the collective
energy a general formula, independent of the details of the single particle
spectrum, is given in both the strong and weak coupling regimes. Next the
displacements of the solutions trapped in between the single particle levels
with respect to the unperturbed energies are explored: their dependence upon a
suitably defined quantum number is found to undergo a transition between two
different regimes.Comment: 30 pages, AMS Latex, 8 figures. Submitted to Phys. Rev.
The pairing Hamiltonian for one pair of identical nucleons bound in a potential well
The problem of one pair of identical nucleons sitting in single
particle levels of a potential well and interacting through the pairing force
is treated introducing even Grassmann variables. The eigenvectors are
analytically expressed solely in terms of these with coefficients fixed by the
eigenvalues and the single particle energies. When the latter are those of an
harmonic oscillator well an accurate expression is derived for both the
collective eigenvalue and for those trapped in between the single particle
levels, for any strength of the pairing interaction and for any number of
levels. Notably the trapped solutions are labelled through an index upon which
they depend parabolically.Comment: 5 pages, 1 postscript figur
Neutral current (anti)neutrino scattering: relativistic mean field and superscaling predictions
We evaluate the neutral current quasi-elastic neutrino cross section within
two nuclear models: the SuSA model, based on the superscaling behavior of
electron scattering data, and the RMF model, based on relativistic mean field
theory. We also estimate the ratio and
compare with the MiniBooNE experimental data, performing a fit of the
parameters and within the two models. Finally, we present our
predictions for antineutrino scattering.Comment: 15 pages, 4 figure
Extensions of Superscaling from Relativistic Mean Field Theory: the SuSAv2 Model
We present a systematic analysis of the quasielastic scaling functions
computed within the Relativistic Mean Field (RMF) Theory and we propose an
extension of the SuperScaling Approach (SuSA) model based on these results. The
main aim of this work is to develop a realistic and accurate phenomenological
model (SuSAv2), which incorporates the different RMF effects in the
longitudinal and transverse nuclear responses, as well as in the isovector and
isoscalar channels. This provides a complete set of reference scaling functions
to describe in a consistent way both processes and the
neutrino/antineutrino-nucleus reactions in the quasielastic region. A
comparison of the model predictions with electron and neutrino scattering data
is presented.Comment: 19 pages, 24 figure
Off-shell effects in the relativistic mean field model and their role in CC (anti)neutrino scattering at MiniBooNE kinematics
The relativistic mean field (RMF) model is used to describe nucleons in the
nucleus and thereby to evaluate the effects of having dynamically off-shell
spinors. Compared with free, on-shell nucleons as employed in some other
models, within the RMF nucleons are described by relativistic spinors with
strongly enhanced lower components. In this work it is seen that for MiniBooNE
kinematics, neutrino charged-current quasielastic cross sections show some
sensitivity to these off-shell effects, while for the antineutrino-nucleus case
the total cross sections are seen to be essentially independent of the
enhancement of the lower components. As was found to be the case when comparing
the RMF results with the neutrino-nucleus data, the present impulse
approximation predictions within the RMF also fall short of the MiniBooNE
antineutrino-nucleus data.Comment: 19 pages, 7 figures, submitted to Physics Letters
Semi-relativistic description of quasielastic neutrino reactions and superscaling in a continuum shell model
The so-called semi-relativistic expansion of the weak charged current in
powers of the initial nucleon momentum is performed to describe
charge-changing, quasielastic neutrino reactions at
intermediate energies. The quality of the expansion is tested by comparing with
the relativistic Fermi gas model using several choices of kinematics of
interest for ongoing neutrino oscillation experiments. The new current is then
implemented in a continuum shell model together with relativistic kinematics to
investigate the scaling properties of and cross
sections.Comment: 33 pages, 10 figures, to appear in PR
Nuclear effects in neutrino and antineutrino CCQE scattering at MINERvA kinematics
We compare the charged-current quasielastic neutrino and antineutrino
observables obtained in two different nuclear models, the phenomenological
SuperScaling Approximation and the Relativistic Mean Field approach, with the
recent data published by the MINERvA Collaboration. Both models provide a good
description of the data without the need of an ad hoc increase in the mass
parameter in the axial-vector dipole form factor. Comparisons are also made
with the MiniBooNE results where different conclusions are reached.Comment: 6 pages, 7 figures, Accepted for publication in Physical Review
Charged-current inclusive neutrino cross sections in the SuperScaling model including quasielastic, pion production and meson-exchange contributions
Charged current inclusive neutrino-nucleus cross sections are evaluated using
the superscaling model for quasielastic scattering and its extension to the
pion production region. The contribution of two-particle-two-hole vector
meson-exchange current excitations is also considered within a fully
relativistic model tested against electron scattering data. The results are
compared with the inclusive neutrino-nucleus data from the T2K and SciBooNE
experiments. For experiments where GeV, the
three mechanisms considered in this work provide good agreement with the data.
However, when the neutrino energy is larger, effects from beyond the
also appear to be playing a role. The results show that processes induced by
two-body currents play a minor role at the kinematics considered.Comment: 10 pages, 7 figure
Nuclear effects in electron reactions and their impact on neutrino processes
We suggest that superscaling in electroweak interactions with nuclei, namely
the observation that the reduced electron-nucleus cross sections are to a large
degree independent of the momentum transfer and of the nuclear species, can be
used as a tool to obtain precise predictions for neutrino-nucleus cross
sections in both charged and neutral current-induced processes.Comment: 11 pages, 7 figures, proceedings of NUINT09, 6th International
Workshop of Neutrino-Nucleus Interactions in the Few-Gev Region, Sitges
(Spain), May 18-22, 200
- …