380 research outputs found
Superscaling in electroweak excitation of nuclei
Superscaling properties of 12C, 16O and 40Ca nuclear responses, induced by
electron and neutrino scattering, are studied for momentum transfer values
between 300 and 700 MeV/c. We have defined two indexes to have quantitative
estimates of the scaling quality. We have analyzed experimental responses to
get the empirical values of the two indexes. We have then investigated the
effects of finite dimensions, collective excitations, meson exchange currents,
short-range correlations and final state interactions. These effects strongly
modify the relativistic Fermi gas scaling functions, but they conserve the
scaling properties. We used the scaling functions to predict electron and
neutrino cross sections and we tested their validity by comparing them with the
cross sections obtained with a full calculation. For electron scattering we
also made a comparison with data. We have calculated the total charge-exchange
neutrino cross sections for neutrino energies up to 300 MeV.Comment: 19 pages, 12 figures, 1 table; to be published in Physical Review
General study of superscaling in quasielastic and reactions using the relativistic impulse approximation
The phenomenon of superscaling for quasielastic lepton induced reactions at
energies of a few GeV is investigated within the framework of the relativistic
impulse approximation. A global analysis of quasielastic inclusive electron and
charged-current neutrino scattering reactions on nuclei is presented. Scaling
and superscaling properties are shown to emerge from both types of processes.
The crucial role played by final state interactions is evaluated by using
different approaches. The asymmetric shape presented by the experimental
scaling function, with a long tail in the region of positive values of the
scaling variable, is reproduced when the interaction in the final state between
the knockout nucleon and the residual nucleus is described within the
relativistic mean field approach. The impact of gauge ambiguities and off-shell
effects in the scaling function is also analyzed.Comment: 34 pages, 14 figures, accepted in Phys. Rev. C. Section II has been
shortene
Neutrino and antineutrino cross sections in C
We extend the formalism of weak interaction processes, obtaining new
expressions for the transition rates, which greatly facilitate numerical
calculations, both for neutrino-nucleus reactions and muon capture. We have
done a thorough study of exclusive (ground state) properties of B and
N within the projected quasiparticle random phase approximation (PQRPA).
Good agreement with experimental data is achieved in this way. The inclusive
neutrino/antineutrino () reactions C(N
and C(B are calculated within both the PQRPA, and
the relativistic QRPA (RQRPA). It is found that the magnitudes of the resulting
cross-sections: i) are close to the sum-rule limit at low energy, but
significantly smaller than this limit at high energies both for and
, ii) they steadily increase when the size of the configuration
space is augmented, and particulary for energies MeV,
and iii) converge for sufficiently large configuration space and final state
spin.Comment: Proceedings of the International Nuclear Physics Conference 2010,
Vancouver, BC - Canada 4-9 Jul 201
Anatomy of relativistic pion loop corrections to the electromagnetic nucleon coupling
We present a relativistic formulation of pion loop corrections to the coupling of photons with nucleons on the light front. Vertex and wave function renormalization constants are computed to lowest order in the pion field, including their nonanalytic behavior in the chiral limit, and studied numerically as a function of the ultraviolet cutoff. Particular care is taken to explicitly verify gauge invariance and Ward-Takahashi identity constraints to all orders in the mπ expansion. The results are used to compute the chiral corrections to matrix elements of local operators, related to moments of deep-inelastic structure functions. Finally, comparison of results for pseudovector and pseudoscalar coupling allows the resolution of a longstanding puzzle in the computation of pion cloud corrections to structure function moments.Chueng-Ryong Ji, W. Melnitchouk, and A.W. Thoma
Neutrino Capture on C
We present neutrino cross sections on C. The charged-current cross
sections leading to various states in the daughter and the
neutral-current cross sections leading to various states in the daughter
C are given. We also provide simple polynomial fits to those cross
sections for quick estimates of the reaction rates. We briefly discuss possible
implications for the current and future scintillator-based experiments.Comment: 5 figure
Neutrino-nucleus interactions at low energies within Fermi-liquid theory
Cross sections are calculated for neutrino scattering off heavy nuclei at
energies below 50 MeV. The theory of Fermi liquid is applied to estimate the
rate of neutrino-nucleon elastic and inelastic scattering in a nuclear medium
in terms of dynamic form factors. The cross sections, obtained here in a rather
simple way, are in agreement with the results of the other much more
sophisticated nuclear models. A background rate from the solar neutrino
interactions within a large Ge detector is estimated in the above-mentioned
approach. The knowledge of the rate is in particular rather important for
new-generation large-scale neutrino experiments.Comment: 9 pages, 6 figure
Muon Capture on Deuteron and 3He: A Personal Review
The present status of theoretical and experimental studies of muon capture
reactions on light nuclei is reviewed. In particular, the recent results for
the two reactions 2H(\mu^-,\nu_\mu)nn and 3He(\mu^-,\nu_\mu)3H are presented,
and the unresolved discrepancies among different measurements and calculations,
open problems, and future developments are discussed.Comment: 19 pages, submitted to International Journal of Modern Physics
Many-Body Theory of the Electroweak Nuclear Response
After a brief review of the theoretical description of nuclei based on
nonrelativistic many-body theory and realistic hamiltonians, these lectures
focus on its application to the analysis of the electroweak response. Special
emphasis is given to electron-nucleus scattering, whose experimental study has
provided a wealth of information on nuclear structure and dynamics, exposing
the limitations of the shell model. The extension of the formalism to the case
of neutrino-nucleus interactions, whose quantitative understanding is required
to reduce the systematic uncertainty of neutrino oscillation experiments, is
also discussed.Comment: Lectures delivered at the DAE-BRNS Workshop on Hadron Physics.
Aligarh Muslim University, Aligarh (India), February 18-23, 200
A new Fermi smearing approach for scattering of multi-GeV electrons by nuclei
The cross section for electron scattering by nuclei at high momentum
transfers is calculated within the Fermi smearing approximation (FSA), where
binding effects on the struck nucleon are introduced via the relativistic
Hartree approximation (RHA). The model naturally preserves current
conservation, since the response tensor for an off-shell nucleon conserves the
same form that for a free one but with an effective mass. Different
parameterizations for the inelastic nucleon structure function, are analyzed.
The smearing at the Fermi surface is introduced through a momentum distribution
obtained from a perturbative nuclear matter calculation. Recent CEBAF data on
inclusive scattering of 4.05 GeV electrons on Fe are well reproduced for
all measured geometries for the first time, as is evident from the comparison
with previous calculations.Comment: 8 pages in Revtex4 style, 6 eps figures, to appear in Physical Review
Nuclear Lattice Simulations with Chiral Effective Field Theory
We study nuclear and neutron matter by combining chiral effective field
theory with non-perturbative lattice methods. In our approach nucleons and
pions are treated as point particles on a lattice. This allows us to probe
larger volumes, lower temperatures, and greater nuclear densities than in
lattice QCD. The low energy interactions of these particles are governed by
chiral effective theory and operator coefficients are determined by fitting to
zero temperature few-body scattering data. Any dependence on the lattice
spacing can be understood from the renormalization group and absorbed by
renormalizing operator coefficients. In this way we have a realistic simulation
of many-body nuclear phenomena with no free parameters, a systematic expansion,
and a clear theoretical connection to QCD. We present results for hot neutron
matter at temperatures 20 to 40 MeV and densities below twice nuclear matter
density.Comment: 41 pages, 23 figure
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