76 research outputs found
Relativistic nuclear structure effects in quasielastic neutrino scattering
Charged-current cross sections are calculated for quasielastic neutrino and
antineutrino scattering using a relativistic meson-nucleon model. We examine
how nuclear-structure effects, such as relativistic random-phase-approximation
(RPA) corrections and momentum-dependent nucleon self-energies, influence the
extraction of the axial form factor of the nucleon. RPA corrections are
important only at low-momentum transfers. In contrast, the momentum dependence
of the relativistic self-energies changes appreciably the value of the
axial-mass parameter, , extracted from dipole fits to the axial form
factor. Using Brookhaven's experimental neutrino spectrum we estimate the
sensitivity of M to various relativistic nuclear-structure effects.Comment: 26 pages, revtex, 6 postscript figures (available upon request
Error propagation in extrapolated nuclear mass predictions
The properties of the error of the nuclear masses calculated from the transverse mass relations are analysed. The work assumes that the calculated errors of the nuclei whose masses are known experimentally behave as a sample selected randomly from a normal population having a zero mean and a standard deviation Ï . It is found that the errors of the calculated masses of nuclei far from the line of beta-stability behave as c 1 d 3/2 where c 1 is a constant and d is the distance of the nucleus from the line of beta-stability. It is shown also that the errors related to the calculated mass differences behave as c 2 d 1/2 where c 2 is another constant.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45826/1/10050_2005_Article_BF01433618.pd
Garvey-Kelson Relations for Nuclear Charge Radii
The Garvey-Kelson relations (GKRs) are algebraic expressions originally
developed to predict nuclear masses. In this letter we show that the GKRs
provide a fruitful framework for the prediction of other physical observables
that also display a slowly-varying dynamics. Based on this concept, we extend
the GKRs to the study of nuclear charge radii. The GKRs are tested on 455 out
of the approximately 800 nuclei whose charge radius is experimentally known. We
find a rms deviation between the GK predictions and the experimental values of
only 0.01 fm. This should be contrasted against some of the most successful
microscopic models that yield rms deviations almost three times as large.
Predictions - with reliable uncertainties - are provided for 116 nuclei whose
charge radius is presently unknown.Comment: 4 pages and 3 figure
Explaining LSND by a decaying sterile neutrino
We propose an explanation of the LSND evidence for electron antineutrino
appearance based on neutrino decay. We introduce a heavy neutrino, which is
produced in pion and muon decays because of a small mixing with muon neutrinos,
and then decays into a scalar particle and a light neutrino, predominantly of
the electron type. We require values of few eV, being the
neutrino--scalar coupling and the heavy neutrino mass, e.g. in the
range from 1 keV to 1 MeV and . Performing a fit to
the LSND data as well as all relevant null-result experiments, we show that all
data can be explained within this decay scenario. In the minimal version of the
decay model, we predict a signal in the upcoming MiniBooNE experiment
corresponding to a transition probability of the same order as seen in LSND. In
addition, we show that extending our model to two nearly degenerate heavy
neutrinos it is possible to introduce CP violation in the decay, which can lead
to a suppression of the signal in MiniBooNE running in the neutrino mode. We
briefly discuss signals in future neutrino oscillation experiments, we show
that our scenario is compatible with bounds from laboratory experiments, and we
comment on implications in astrophysics and cosmology.Comment: 23 pages, 5 figures, minor improvements, matches published versio
Principle of Balance and the Sea Content of the Proton
In this study, the proton is taken as an ensemble of quark-gluon Fock states.
Using the principle of balance that every Fock state should be balanced with
all of the nearby Fock states (denoted as the balance model), instead of the
principle of detailed balance that any two nearby Fock states should be
balanced with each other (denoted as the detailed balance model), the
probabilities of finding every Fock state of the proton are obtained. The
balance model can be taken as a revised version of the detailed balance model,
which can give an excellent description of the light flavor sea asymmetry
(i.e., ) without any parameter. In case of
sub-processes not considered, the balance model and the
detailed balance model give the same results. In case of
sub-processes considered, there is about 10 percent difference between the
results of these models. We also calculate the strange content of the proton
using the balance model under the equal probability assumption.Comment: 32 latex pages, 4 ps figures, to appear in PR
Recoil Order Chiral Corrections to Baryon Octet Axial Currents and Large QCD
We compute the chiral corrections to octet baryon axial currents through
in heavy baryon chiral perturbation theory, including both
octet and decuplet baryon intermediate states. We include the latter in a
consistent way by using the small scale expansion. We find that, in contrast to
the situation at , there exist no cancellations between octet
and decuplet contributions at . Consequently, the corrections spoil the expected scaling behavior of the chiral
expansion. We discuss this result in terms of the expansion. We also
consider the implications for determination of the strange quark contribution
to the nucleon spin from polarized deep inelastic scattering data.Comment: 7 page
Deuteron Electroweak Disintegration
We study the deuteron electrodisintegration with inclusion of the neutral
currents focusing on the helicity asymmetry of the exclusive cross section in
coplanar geometry. We stress that a measurement of this asymmetry in the quasi
elastic region is of interest for an experimental determination of the weak
form factors of the nucleon, allowing one to obtain the parity violating
electron neutron asymmetry. Numerically, we consider the reaction at low
momentum transfer and discuss the sensitivity of the helicity asymmetry to the
strangeness radius and magnetic moment. The problems coming from the finite
angular acceptance of the spectrometers are also considered.Comment: 30 pages, Latex, 7 eps figures, submitted to Phys.Rev.C e-mail:
[email protected] , [email protected]
Detection of Supernova Neutrinos by Neutrino-Proton Elastic Scattering
We propose that neutrino-proton elastic scattering, ,
can be used for the detection of supernova neutrinos in scintillator detectors.
Though the proton recoil kinetic energy spectrum is soft, with , and the scintillation light output from slow, heavily ionizing
protons is quenched, the yield above a realistic threshold is nearly as large
as that from . In addition, the measured proton
spectrum is related to the incident neutrino spectrum, which solves a
long-standing problem of how to separately measure the total energy and
temperature of , , , and .
The ability to detect this signal would give detectors like KamLAND and
Borexino a crucial and unique role in the quest to detect supernova neutrinos.Comment: 10 pages, 9 figures, revtex
Non-perturbative structure of the polarized nucleon sea
We investigate the flavour and quark-antiquark structure of the polarized
nucleon by calculating the parton distribution functions of the nucleon sea
using the meson cloud model. We find that the SU(2) flavor symmetry in the
light antiquark sea and quark-antiquark symmetry in the strange quark sea are
broken, {\it i.e.} \Delta\ubar < \Delta \dbar and \Delta s < \Delta \sbar.
The polarization of the strange sea is found to be positive, which is in
contradiction to previous analyses. We predict a much larger quark-antiquark
asymmetry in the polarized strange quark sea than that in the unpolarized
strange quark sea. Our results for both polarized light quark sea and polarized
strange quark sea are consistent with the recent HERMES data.Comment: RevTex, 17 pages plus 8 PS figure
Isospin breaking corrections to nucleon form factors in the constituent quark model
We examine isospin breaking in the nucleon wave functions due to the
quark mass difference and the Coulomb interaction among the quarks, and their
consequences on the nucleon electroweak form factors in a nonrelativistic
constituent quark model. The mechanically induced isospin breaking in the
nucleon wave functions and electroweak form factors are exactly evaluated in
this model. We calculate the electromagnetically induced isospin admixtures by
using first-order perturbation theory, including the lowest-lying resonance
with nucleon quantum numbers but isospin 3/2. We find a small (), but
finite correction to the anomalous magnetic moments of the nucleon stemming
almost entirely from the quark mass difference, while the static nucleon axial
coupling remains uncorrected. Corrections of the same order of magnitude appear
in charge, magnetic, and axial radii of the nucleon. The correction to the
charge radius in this model is primarily isoscalar, and may be of some
significance for the extraction of the strangeness radius from e.g. elastic
forward angle parity violating electron-proton asymmetries, or elastic
experiments.Comment: 15 pp(22 as preprint), revtex, 3 uuencoded figs at end of this fil
- âŠ