6,018 research outputs found
Parity-Violating Electron Scattering from the Pion-Correlated Relativistic Fermi Gas
Parity-violating quasielastic electron scattering is studied within the
context of the relativistic Fermi gas and its extensions to include the effects
of pionic correlations and meson-exchange currents. The work builds on previous
studies using the same model; here the part of the parity-violating asymmetry
that contains axial-vector hadronic currents is developed in detail using those
previous studies and a link is provided to the transverse vector-isovector
response. Various integrated observables are constructed from the differential
asymmetry. These include an asymmetry averaged over the quasielastic peak, as
well as the difference of the asymmetry integrated to the left and right of the
peak -- the latter is shown to be optimal for bringing out the nature of the
pionic correlations. Special weighted integrals involving the differential
asymmetry and electromagnetic cross section, based on the concepts of y-scaling
and sum rules, are constructed and shown to be suited to studies of the
single-nucleon form factor content in the problem, in particular, to
determinations of the isovector/axial-vector and electric strangeness form
factors. Comparisons are also made with recent predictions made on the basis of
relativistic mean-field theory.Comment: 28 pages, LATeX, 13 figures (tar-compressed postscript files,
available from the authors), MIT preprint CTP#222
Superscaling in electron- and neutrino-nucleus scattering
The superscaling properties of electron scattering data are used to extract
model-independent predictions for neutrino-nucleus cross sections.Comment: Contibution to NuInt05, 4th international workshop on
neutrino-nucleus interaction in the few GeV region, Sept. 26 - 29 2005,
Okayama, Japa
Parity-violating longitudinal response
The longitudinal quasielastic parity-violating electron scattering response
is explored within the context of a model that builds antisymmetrized RPA-HF
correlations on a relativistic Fermi gas basis. The large sensitivity to
nuclear dynamics of this observable, found in previous studies where only
pionic correlations were included, is shown to survive in the present model
where the effects from pion, rho, sigma and omega exchange in a version of the
Bonn potential are incorporated. Through an intricate diagrammatic
cancellation/filtration mechanism the longitudinal parity-violating response
turns out to be close to the one obtained in first-order perturbation theory
with the pion alone. Finally, in accord with our previous work, the
parity-violating response is seen to display appreciable sensitivity to the
electric strangeness content of the nucleon, especially at high momentum
transfer.Comment: 13 pages, uses REVTeX and epsfig, 10 postscript figures; a postscript
version of the paper is available by anonymous ftp at
ftp://carmen.to.infn.it/pub/barbaro/papers/951
Spectral Geometry and One-loop Divergences on Manifolds with Conical Singularities
Geometrical form of the one-loop divergences induced by conical singularities
of background manifolds is studied. To this aim the heat kernel asymptotic
expansion on spaces having the structure near
singular surface is analysed. Surface corrections to standard second
and third heat coefficients are obtained explicitly in terms of angle
of a cone and components of the Riemann tensor. These results are
compared to ones to be already known for some particular cases. Physical
aspects of the surface divergences are shortly discussed.Comment: preprint DSF-13/94, 13 pages, latex fil
The 2p-2h electromagnetic response in the quasielastic peak and beyond
The contribution to the nuclear transverse response function R_T arising from
two particle-two hole (2p-2h) states excited through the action of
electromagnetic meson exchange currents (MEC) is computed in a fully
relativistic framework. The MEC considered are those carried by the pion and by
Delta degrees of freedom, the latter being viewed as a virtual nucleonic
resonance. The calculation is performed in the relativistic Fermi gas model in
which Lorentz covariance can be maintained. All 2p-2h many-body diagrams
containing two pionic lines that contribute to R_T are taken into account and
the relative impact of the various components of the MEC on R_T is addressed.
The non-relativistic limit of the MEC contributions is also discussed and
compared with the relativistic results to explore the role played by relativity
in obtaining the 2p-2h nuclear response.Comment: 27 pages, 12 figures, revtex4; minor modifications in the discussion
of the results, references adde
Inclusive quasielastic scattering of polarized electrons from polarized nuclei
The inclusive quasielastic response functions that appear in the scattering
of polarized electrons from polarized nuclei are computed and analyzed for
several closed-shell-minus-one nuclei with special attention paid to 39K.
Results are presented using two models for the ejected nucleon --- when
described by a distorted wave in the continuum shell model or by a plane wave
in PWIA with on- and off-shell nucleons. Relativistic effects in kinematics and
in the electromagnetic current have been incorporated throughout. Specifically,
the recently obtained expansion of the electromagnetic current in powers only
of the struck nucleon's momentum is employed for the on-shell current and the
effects of the first-order terms (spin-orbit and convection) are compared with
the zeroth-order (charge and magnetization) contributions. The use of polarized
inclusive quasielastic electron scattering as a tool for determining
near-valence nucleon momentum distributions is discussed.Comment: 51 LaTeX pages, 14 Postscript figure
Inelastic electron-nucleus scattering and scaling at high inelasticity
Highly inelastic electron scattering is analyzed within the context of the
unified relativistic approach previously considered in the case of quasielastic
kinematics. Inelastic relativistic Fermi gas modeling that includes the
complete inelastic spectrum - resonant, non-resonant and Deep Inelastic
Scattering - is elaborated and compared with experimental data. A
phenomenological extension of the model based on direct fits to data is also
introduced. Within both models, cross sections and response functions are
evaluated and binding energy effects are analyzed. Finally, an investigation of
the second-kind scaling behavior is also presented.Comment: 39 pages, 13 figures; formalism extended and slightly reorganized,
conclusions extended; to appear in Phys. Rev.
Role of 2p-2h MEC excitations in superscaling
Following recent studies of inclusive electron scattering from nuclei at high
energies which focused on two-nucleon emission mediated by meson-exchange
currents, in this work the superscaling behavior of such contributions is
investigated. Comparisons are made with existing data below the quasielastic
peak where at high momentum transfers scaling of the second kind is known to be
excellent and scaling of the first kind is good, in the proximity of the peak
where both 1p-1h and 2p-2h contributions come into play, and above the peak
where inelasticity becomes important and one finds scaling violations of the
two kinds.Comment: 27 pages, 12 figures; references adde
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