6,124 research outputs found
A simple model for NN correlations in quasielastic lepton-nucleus scattering
We present a covariant extension of the relativistic Fermi gas model which
incorporates correlation effects in nuclei. Within this model, inspired by the
BCS descriptions of systems of fermions, we obtain the nuclear spectral
function and from it the superscaling function for use in treating high-energy
quasielastic electroweak processes. Interestingly, this model has the
capability to yield the asymmetric tail seen in the experimental scaling
function.Comment: 11 pages, 6 figures, Proceedings of the Twenty Seventh International
Workshop on Nuclear Theory, June 23 - 28, 2008, Rila mountains, Bulgari
Mass flow through solid 4He induced by the fountain effect
Using an apparatus that allows superfluid liquid 4He to be in contact with
hcp solid \4he at pressures greater than the bulk melting pressure of the
solid, we have performed experiments that show evidence for 4He mass flux
through the solid and the likely presence of superfluid inside the solid. We
present results that show that a thermomechanical equilibrium in quantitative
agreement with the fountain effect exists between two liquid reservoirs
connected to each other through two superfluid-filled Vycor rods in series with
a chamber filled with solid 4He. We use the thermomechanical effect to induce
flow through the solid and measure the flow rate. On cooling, mass flux appears
near T = 600 mK and rises smoothly as the temperature is lowered. Near T = 75
mK a sharp drop in the flux is present. The flux increases as the temperature
is reduced below 75 mK. We comment on possible causes of this flux minimum.Comment: 20 pages, 22 figures, 7 table
Quasielastic Charged Current Neutrino-nucleus Scattering
We provide integrated cross sections for quasielastic charged-current
neutrino-nucleus scattering. Results evaluated using the phenomenological
scaling function extracted from the analysis of experimental data are
compared with those obtained within the framework of the relativistic impulse
approximation. We show that very reasonable agreement is reached when a
description of final-state interactions based on the relativistic mean field is
included. This is consistent with previous studies of differential cross
sections which are in accord with the universality property of the superscaling
function.Comment: 5 pages, 3 figures, to be published in Phys. Rev. Let
Superscaling Predictions for Neutral Current Quasielastic Neutrino-Nucleus Scattering
The application of superscaling ideas to predict neutral-current (NC)
quasielastic (QE) neutrino cross sections is investigated. Results obtained
within the relativistic impulse approximation (RIA) using the same relativistic
mean field potential (RMF) for both initial and final nucleons -- a model that
reproduces the experimental (e,e') scaling function -- are used to illustrate
the ideas involved. While NC reactions are not so well suited for scaling
analyses, to a large extent the RIA-RMF predictions do exhibit superscaling.
Independence of the scaled response on the nuclear species is very well
fulfilled. The RIA-RMF NC superscaling function is in good agreement with the
experimental (e,e') one. The idea that electroweak processes can be described
with a universal scaling function, provided that mild restrictions on the
kinematics are assumed, is shown to be valid.Comment: 4 pages, 4 figures, published in PR
Relativistic Models for Quasi-Elastic Neutrino-Nucleus Scattering
Two relativistic approaches to charged-current quasielastic neutrino-nucleus
scattering are illustrated and compared: one is phenomenological and based on
the superscaling behavior of electron scattering data and the other relies on
the microscopic description of nuclear dynamics in relativistic mean field
theory. The role of meson exchange currents in the two-particle two-hole sector
is explored. The predictions of the models for differential and total cross
sections are presented and compared with the MiniBooNE data.Comment: 3 pages, 3 figures, Proceedings of PANIC 2011, MIT, Cambridge, MA,
July 201
Pionic correlations and meson-exchange currents in two-particle emission induced by electron scattering
Two-particle two-hole contributions to electromagnetic response functions are
computed in a fully relativistic Fermi gas model. All one-pion exchange
diagrams that contribute to the scattering amplitude in perturbation theory are
considered, including terms for pionic correlations and meson-exchange currents
(MEC). The pionic correlation terms diverge in an infinite system and thus are
regularized by modification of the nucleon propagator in the medium to take
into account the finite size of the nucleus. The pionic correlation
contributions are found to be of the same order of magnitude as the MEC.Comment: 14 pages, 15 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
- …