4,513 research outputs found
Strangeness on the nucleon
Observables from parity violation in elastic electron-nucleon scattering and
neutral current quasi-elastic neutrino-nucleus scattering are employed as tools
to improve the current knowledge on the strangeness content in the nucleon.Comment: Proceedings of International Scientific Meeting on Nuclear Physics,
9-13th September 2012. La R\'abida, Huelva, Spai
Pion production within the hybrid relativistic plane wave impulse approximation model at MiniBooNE and MINERvA kinematics
The hybrid model for electroweak single-pion production (SPP) off the
nucleon, presented in [Gonz\'alez-Jim\'enez et al., Phys. Rev. D 95, 113007
(2017)], is extended here to the case of incoherent pion-production on the
nucleus. Combining a low-energy model with a Regge approach, this model
provides valid predictions in the entire energy region of interest for current
and future accelerator-based neutrino-oscillation experiments. The Relativistic
Mean-Field model is used for the description of the bound nucleons while the
outgoing hadrons are considered as plane waves. This approach, known as
Relativistic Plane-Wave Impulse Approximation (RPWIA), is a first step towards
the development of more sophisticated models, it is also a test of our current
understanding of the elementary reaction. We focus on the charged-current
()-nucleus interaction at MiniBooNE and MINERvA kinematics. The
effect on the cross sections of the final-state interactions, which affect the
outgoing hadrons on their way out of the nucleus, is judged by comparing our
results with those from the NuWro Monte Carlo event generator. We find that the
hybrid-RPWIA predictions largely underestimate the MiniBooNE data. In the case
of MINERvA, our results fall below the -induced 1 production data,
while a better agreement is found for -induced 1 and
-induced 1 production.Comment: 13 pages, 10 figure
Parity violation in quasielastic electron-nucleus scattering within the relativistic impulse approximation
We study parity violation in quasielastic (QE) electron-nucleus scattering
using the relativistic impulse approximation. Different fully relativistic
approaches have been considered to estimate the effects associated with the
final-state interactions. We have computed the parity-violating quasielastic
(PVQE) asymmetry and have analyzed its sensitivity to the different ingredients
that enter in the description of the reaction mechanism: final-state
interactions, nucleon off-shellness effects, current gauge ambiguities.
Particular attention has been paid to the description of the weak neutral
current form factors. The PVQE asymmetry is proven to be an excellent
observable when the goal is to get precise information on the axial-vector
sector of the weak neutral current. Specifically, from measurements of the
asymmetry at backward scattering angles good knowledge of the radiative
corrections entering in the isovector axial-vector sector can be gained.
Finally, scaling properties shown by the interference nuclear
responses are also analyzed.Comment: 15 pages, 11 figure
Parity violation and dynamical relativistic effects in reactions
It is well known that coincidence quasielastic reactions are
not appropriate to analyze effects linked to parity violation due the presence
of the fifth electromagnetic (EM) response . Nevertheless, in this
work we develop a fully relativistic approach to be applied to parity-violating
(PV) quasielastic processes. This is of importance as a
preliminary step in the subsequent study of inclusive quasielastic PV
reactions. Moreover, our present analysis allows us to
disentangle effects associated with the off-shell character of nucleons in
nuclei, gauge ambiguities and the role played by the lower components in the
nucleon wave functions, i.e., dynamical relativistic effects. This study can
help in getting clear information on PV effects. Particular attention is paid
to the relativistic plane-wave impulse approximation where the explicit
expressions for the PV single-nucleon responses are shown for the first time.Comment: 39 pages, 9 figure
Global analysis of parity-violating asymmetry data for elastic electron scattering
We perform a statistical analysis of the full set of parity-violating
asymmetry data for elastic electron scattering including the most recent high
precision measurement from -weak. Given the basis of the present analysis,
our estimates appear to favor non-zero vector strangeness, specifically,
positive (negative) values for the electric (magnetic) strange form factors. We
also provide an accurate estimate of the axial-vector nucleon form factor at
zero momentum transfer, . Our study shows to be
importantly reduced with respect to the currently accepted value. We also find
our analysis of data to be compatible with the Standard Model values for the
weak charges of the proton and neutron.Comment: 6 pages, 4 figures, 2 tables. Accepted for publication in PR
Seagull and pion-in-flight currents in neutrino-induced and knockout
[Background] The neutrino-nucleus () cross section is a major source
of systematic uncertainty in neutrino-oscillation studies. A precise
scattering model, in which multinucleon effects are incorporated, is pivotal
for an accurate interpretation of the data. [Purpose] In interactions,
meson-exchange currents (MECs) can induce two-nucleon () knockout from the
target nucleus, resulting in a two-particle two-hole (2p2h) final state. They
also affect single nucleon () knockout reactions, yielding a one-particle
one-hole (1p1h) final state. Both channels affect the inclusive strength. We
present a study of axial and vector, seagull and pion-in-flight currents in
muon-neutrino induced and knockout reactions on C. [Method]
Bound and emitted nucleons are described as Hartree-Fock wave functions. For
the vector MECs, the standard expressions are used. For the axial current,
three parameterizations are considered. The framework developed here allows for
a treatment of MECs and short-range correlations (SRCs). [Results] Results are
compared with electron-scattering data and with literature. The strengths of
the seagull, pion-in-flight and axial currents are studied separately and
double differential cross sections including MECs are compared with results
including SRCs. A comparison with MiniBooNE and T2K data is presented.
[Conclusions] In the 1p1h channel, the effects of the MECs tend to cancel each
other, resulting in a small effect on the double differential cross section.
knockout processes provide a small contribution to the inclusive double
differential cross section, ranging from the knockout threshold into the
dip region. A fair agreement with the MiniBooNE and T2K data is reached.Comment: 16 pages, 10 figure
Impact of low-energy nuclear excitations on neutrino-nucleus scattering at MiniBooNE and T2K kinematics
[Background] Meticulous modeling of neutrino-nucleus interactions is
essential to achieve the unprecedented precision goals of present and future
accelerator-based neutrino-oscillation experiments. [Purpose] Confront our
calculations of charged-current quasielastic cross section with the
measurements of MiniBooNE and T2K, and to quantitatively investigate the role
of nuclear-structure effects, in particular, low-energy nuclear excitations in
forward muon scattering. [Method] The model takes the mean-field (MF) approach
as the starting point, and solves Hartree-Fock (HF) equations using a Skyrme
(SkE2) nucleon-nucleon interaction. Long-range nuclear correlations are taken
into account by means of the continuum random-phase approximation (CRPA)
framework. [Results] We present our calculations on flux-folded double
differential, and flux-unfolded total cross sections off C and compare
them with MiniBooNE and (off-axis) T2K measurements. We discuss the importance
of low-energy nuclear excitations for the forward bins. [Conclusions] The CRPA
predictions describe the gross features of the measured cross sections. They
underpredict the data (more in the neutrino than in the antineutrino case)
because of the absence of processes beyond pure quasielastic scattering in our
model. At very forward muon scattering, low-energy nuclear excitations ( 50 MeV) account for nearly 50% of the flux-folded cross section.Comment: 8 pages, 9 figures. Version published in Physical Review
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