188 research outputs found
Extracting the Weinberg angle at intermediate energies
A recent experiment by the NuTeV collaboration resulted in a surprisingly
high value for the weak mixing angle . The Paschos-Wolfenstein
relation, relating neutrino cross sections to the Weinberg angle, is of pivotal
importance in the NuTeV analysis. In this work, we investigate the sensitivity
of the Paschos-Wolfenstein relation to nuclear structure aspects at neutrino
energies in the few GeV range. Neutrino-nucleus cross sections are calculated
for O and Fe target nuclei within a relativistic quasi-elastic
nucleon-knockout model.Comment: To appear in the proceedings of International School of Nuclear
Physics: 27th Course: "Neutrinos in Cosmology, in Astro, Particle and Nuclear
Physics", Erice, Sicily, Italy, 16-24 Sep 200
Identifying neutrinos and antineutrinos in neutral-current scattering reactions
We study neutrino-induced nucleon knockout from nuclei. Expressions for the
induced polarization are derived within the framework of the
independent-nucleon model and the non-relativistic plane-wave approximation.
Large dissimilarities in the nucleon polarization asymmetries are observed
between neutrino- and antineutrino-induced processes. These asymmetries
represent a potential way to distinguish between neutrinos and antineutrinos in
neutral-current neutrino-scattering on nuclei. We discuss astrophysical
applications of these polarization asymmetries. Our findings are illustrated
for neutrino scattering on O and Pb.Comment: 5 pages, 5 figures, accepted for publication in Phys. Rev. Let
Electroweak interactions in a relativistic Fermi gas
We present a relativistic model for computing the neutrino mean free path in
neutron matter. Thereby, neutron matter is described as a non-interacting Fermi
gas in beta-equilibrium. We present results for the neutrino mean free path for
temperatures from 0 up to 50 MeV and a broad range of neutrino energies. We
show that relativistic effects cause a considerable enhancement of
neutrino-scattering cross-sections in neutron matter. The influence of the
-dependence in the electroweak form factors and the inclusion of a weak
magnetic term in the hadron current is discussed. The weak-magnetic term in the
hadron current is at the origin of some selective spin dependence for the
nucleons which are subject to neutrino interactions.Comment: 11 pages, 7 figures, accepted to Phys. Rev. C, minor changes and
updates of the figures are mad
Relativistic effects in neutrino-Fermi gas interactions
We study neutrino interactions in a hadron gas within a relativistic
framework. The hadron matter is described by a non-interacting Fermi gas in
beta equilibrium. We show that the introduction of relativistic effects causes
a sizable enhancement of the neutrino-scattering cross sections.Comment: To appear in the proceedings of International School of Nuclear
Physics: 27th Course: "Neutrinos in Cosmology, in Astro, Particle and Nuclear
Physics". Erice, Sicily, Italy, 16-2
Spin-dependent neutrino-induced nucleon knockout
We study neutrino-induced nucleon knockout off atomic nuclei and examine the
polarization properties of the ejectile. A detailed study of the spin
dependence of the outgoing nucleon is presented. The numerical results are
derived within a non-relativistic plane-wave impulse-approximation approach.
Our calculations reveal large polarization asymmetries, and clear
dissimilarities between neutrino- and antineutrino-induced reactions. They
reflect the fact that neutrino-induced nucleon knockout is dominated by the
transverse axial current and gains its major contributions from forward nucleon
emission and backward lepton scattering.Comment: 9 pages, 7 figures, accepted for publication in Phys. Rev.
Strangeness content of the nucleon in quasielastic neutrino-nucleus reactions
We present a systematic study of the sensitivity of quasielastic
neutrino-nucleus cross sections at intermediate energies to the strange quark
sea of the nucleon. To this end, we investigate the impact of the weak
strangeness form factors on the ratio of proton-to-neutron knockout, the ratio
of neutral-to-charged current cross sections, on the Paschos-Wolfenstein
relation, and on the longitudinal helicity asymmetry. The influence of axial as
well as vector strangeness effects is discussed. For the latter, we introduce
strangeness parameters from various hadron models and from a recent fit to data
from parity violating electron scattering.
In our model, the nuclear target is described in terms of a relativistic
mean-field approach. The effects of final-state interactions on the outgoing
nucleon are quantified within a relativistic multiple-scattering Glauber
approach. Our results are illustrated with cross sections for the scattering of
1 GeV neutrinos and antineutrinos off a C target.
Folding with a proposed FINeSSE (anti)neutrino energy-distribution has no
qualitative influence on the overall sensitivity of the cross-section ratios to
strangeness mechanisms. We show that vector strangeness effects are large and
strongly dependent.Comment: 25 pages, 12 figures, submitted to Phys. Rev.
Quasielastic electron- and neutrino-nucleus scattering in a continuum random phase approximation approach
We present a continuum random phase approximation approach to study electron-
and neutrino-nucleus scattering cross sections, in the kinematic region where
quasielastic scattering is the dominant process. We show the validity of the
formalism by confronting inclusive () cross sections with the available
data. We calculate flux-folded cross sections for charged-current quasielastic
antineutrino scattering off C and compare them with the MiniBooNE
cross-section measurements. We pay special emphasis to the contribution of
low-energy nuclear excitations in the signal of accelerator-based
neutrino-oscillation experiments.Comment: 5 pages, 5 figures. Contribution to the proceedings of the 16th
International Workshop on Neutrino Factories and Future Neutrino Beam
Facilities (NUFACT-2014
Quasielastic contribution to antineutrino-nucleus scattering
We report on a calculation of cross sections for charged-current quasielastic
antineutrino scattering off C in the energy range of interest for the
MiniBooNE experiment. We adopt the impulse approximation (IA) and use the
nonrelativistic continuum random phase approximation (CRPA) to model the
nuclear dynamics. An effective nucleon-nucleon interaction of the Skyrme type
is used. We compare our results with the recent MiniBooNE antineutrino
cross-section data and confront them with alternate calculations. The CRPA
predictions reproduce the gross features of the shape of the measured
double-differential cross sections. The CRPA cross sections are typically
larger than those of other reported IA calculations but tend to underestimate
the magnitude of the MiniBooNE data. We observe that an enhancement of the
nucleon axial mass in CRPA calculations is an effective way of improving on the
description of the shape and magnitude of the double-differential cross
sections. The rescaling of is illustrated to affect the shape of the
double-differential cross sections differently than multinucleon effects beyond
the IA.Comment: 10 pages, 10 figures. Version published in Physical Review
Helicity asymmetries in neutrino-nucleus interactions
We investigate the helicity properties of the ejectile in quasi-elastic
neutrino-induced nucleon-knockout reactions and consider the 12C target as a
test case. A formalism based on a relativistic mean-field model is adopted. The
influence of final-state interactions is evaluated within a relativistic
multiple-scattering Glauber approximation (RMSGA) model. Our calculations
reveal that the helicity asymmetries A_l in A(\overline{\nu},\overline{\nu}'N)
processes are extremely sensitive to strange-quark contributions to the weak
vector form-factors. Thereby, nuclear corrections, such as final-state
interactions and off-shell ambiguities in the electroweak current operators,
are observed to be of marginal importance. This facilitates extracting
strange-quark information from the helicity asymmetry A_l.Comment: 14 pages, 6 figures, 1 table submitted to PL
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
- âŠ