59 research outputs found
Do Hadronic Charge Exchange Reactions Measure Electroweak L = 1 Strength?
An eikonal model has been used to assess the relationship between calculated
strengths for first forbidden beta decay and calculated cross sections for
(p,n) charge exchange reactions. It is found that these are proportional for
strong transitions, suggesting that hadronic charge exchange reactions may be
useful in determining the spin-dipole matrix elements for astrophysically
interesting leptonic transitions.Comment: 14 pages, 5 figures, Submitted to Physical Review
A Global Potential Analysis of the O+Si Reaction Using a New Type of Coupling Potential
A new approach has been used to explain the experimental data for the
O+Si system over a wide energy range in the laboratory system
from 29.0 to 142.5 MeV. A number of serious problems has continued to plague
the study of this system for a couple of decades. The explanation of anomalous
large angle scattering data; the reproduction of the oscillatory structure near
the Coulomb barrier; the out-of-phase problem between theoretical predictions
and experimental data; the consistent description of angular distributions
together with excitation functions data are just some of these problems. These
are long standing problems that have persisted over the years and do represent
a challenge calling for a consistent framework to resolve these difficulties
within a unified approach. Traditional frameworks have failed to describe these
phenomena within a single model and have so far only offered different
approaches where these difficulties are investigated separately from one
another. The present work offers a plausible framework where all these
difficulties are investigated and answered. Not only it improves the
simultaneous fits to the data of these diverse observables, achieving this
within a unified approach over a wide energy range, but it departs for its
coupling potential from the standard formulation. This new feature is shown to
improve consistently the agreement with the experimental data and has made
major improvement on all the previous coupled-channels calculations for this
system.Comment: 21 pages with 12 figure
The Role of Final State Interactions in Quasielastic Fe Reactions at large
A relativistic finite nucleus calculation using a Dirac optical potential is
used to investigate the importance of final state interactions [FSI] at large
momentum transfers in inclusive quasielastic electronuclear reactions. The
optical potential is derived from first-order multiple scattering theory and
then is used to calculate the FSI in a nonspectral Green's function doorway
approach. At intermediate momentum transfers excellent predictions of the
quasielastic Fe experimental data for the longitudinal response
function are obtained. In comparisons with recent measurements at ~GeV/c the theoretical calculations of give good agreement for
the quasielastic peak shape and amplitude, but place the position of the peak
at an energy transfer of about ~MeV higher than the data.Comment: 13 pages typeset using revtex 3.0 with 6 postscript figures in
accompanying uuencoded file; submitted to Phys. Rev.
Complete Set of Polarization Transfer Observables for the Reaction at 296 MeV and 0
A complete set of polarization transfer observables has been measured for the
reaction at and . The total spin transfer and the observable
deduced from the measured polarization transfer observables indicate that
the spin--dipole resonance at has greater
strength than strength, which is consistent with recent experimental and
theoretical studies. The results also indicate a predominance of the spin-flip
and unnatural-parity transition strength in the continuum. The exchange tensor
interaction at a large momentum transfer of is
discussed.Comment: 4 pages, 4 figure
Quasi-Elastic Scattering in the Inclusive (He, t) Reaction
The triton energy spectra of the charge-exchange C(He,t) reaction
at 2 GeV beam energy are analyzed in the quasi-elastic nucleon knock-out
region. Considering that this region is mainly populated by the charge-exchange
of a proton in He with a neutron in the target nucleus and the final proton
going in the continuum, the cross-sections are written in the distorted-wave
impulse approximation. The t-matrix for the elementary exchange process is
constructed in the DWBA, using one pion- plus rho-exchange potential for the
spin-isospin nucleon- nucleon potential. This t-matrix reproduces the
experimental data on the elementary pn np process. The calculated
cross-sections for the C(He,t) reaction at to triton
emission angle are compared with the corresponding experimental data, and are
found in reasonable overall accord.Comment: 19 pages, latex, 11 postscript figures available at
[email protected], submitted to Phy.Rev.
Polarization transfer in the O reaction at forward angles and structure of the spin-dipole resonances
Cross sections and polarization transfer observables in the O
reactions at 392 MeV were measured at several angles between
0 and 14. The non-spin-flip () and spin-flip
() strengths in transitions to several discrete states and broad
resonances in O were extracted using a model-independent method. The
giant resonances in the energy region of 27 MeV were found to be
predominantly excited by transitions. The strength distribution
of spin-dipole transitions with and were deduced.
The obtained distribution was compared with a recent shell model calculation.
Experimental results are reasonably explained by distorted-wave impulse
approximation calculations with the shell model wave functions.Comment: 28 pages RevTex, including 9 figures, to be published in Phys. Rev.
C.; a typo in Eq. (3b) was correcte
Microscopic calculations of medium effects for 200-MeV (p,p') reactions
We examine the quality of a G-matrix calculation of the effective
nucleon-nucleon (NN) interaction for the prediction of the cross section and
analyzing power for 200-MeV (p,p') reactions that populate natural parity
states in O, Si, and Ca. This calculation is based on a
one-boson-exchange model of the free NN force that reproduces NN observables
well. The G-matrix includes the effects of Pauli blocking, nuclear binding, and
strong relativistic mean-field potentials. The implications of adjustments to
the effective mass ansatz to improve the quality of the approximation at
momenta above the Fermi level will be discussed, along with the general quality
of agreement to a variety of (p,p') transitions.Comment: 36 pages, TeX, 18 figure
Coupled-channels analysis of the O+Pb fusion barrier distribution
Analyses using simplified coupled-channels models have been unable to
describe the shape of the previously measured fusion barrier distribution for
the doubly magic O+Pb system. This problem was investigated by
re-measuring the fission excitation function for O+Pb with
improved accuracy and performing more exact coupled-channels calculations,
avoiding the constant-coupling and first-order coupling approximations often
used in simplified analyses. Couplings to the single- and 2-phonon states of
Pb, correctly taking into account the excitation energy and the phonon
character of these states, particle transfers, and the effects of varying the
diffuseness of the nuclear potential, were all explored. However, in contrast
to other recent analyses of precise fusion data, no satisfactory simultaneous
description of the shape of the experimental barrier distribution and the
fusion cross-sections for O+Pb was obtained.Comment: RevTex, 29 pages, 7 postscript figures, to appear in PR
Nuclear Transparency to Intermediate-Energy Protons
Nuclear transparency in the (e,e'p) reaction for 135 < Tp < 800 MeV is
investigated using the distorted wave approximation. Calculations using
density-dependent effective interactions are compared with phenomenological
optical potentials. Nuclear transparency is well correlated with proton
absorption and neutron total cross sections. For Tp < 300 MeV there is
considerable sensitivity to the choice of optical model, with the empirical
effective interaction providing the best agreement with transparency data. For
Tp > 300 MeV there is much less difference between optical models, but the
calculations substantially underpredict transparency data and the discrepancy
increases with A. The differences between Glauber and optical model
calculations are related to their respective definitions of the semi-inclusive
cross section. By using a more inclusive summation over final states the
Glauber model emphasizes nucleon-nucleon inelasticity, whereas with a more
restrictive summation the optical model emphasizes nucleon-nucleus
inelasticity; experimental definitions of the semi-inclusive cross section lie
between these extremes.Comment: uuencoded gz-compressed tar file containing revtex and bbl files and
5 postscript figures, totalling 31 pages. Uses psfi
Production and decay of the d* dibaryon
The production of the isoscalar Jp = 3+ didelta dibaryon d* by proton
inelastic scattering from deuteron targets is described in a double-scattering
Glauber approximation. Each scattering changes a target nucleon into a Delta
with the help of the isovector tensor force transmitted by pi and rho mesons.
The differential cross section constructed from empirical Love-Franey
nucleon-nucleon t-matrices and a simple model of d* shows a maximum of some 10
micro-b/sr at 70 deg (c.m.) for 500 MeV protons. The partial width of the decay
d* -> NN caused by the exchanges of the same mesons is found for this simple
model of d* to be about 9 MeV if the d* mass is 2100 MeV. The implications of
these results are discussed.Comment: 31 pages, 8 figure
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