81 research outputs found
Complete set of polarization transfer coefficients for the reaction at 346 MeV and 0 degrees
We report measurements of the cross-section and a complete set of
polarization transfer coefficients for the reaction at a
bombarding energy = 346 MeV and a reaction angle =
.
The data are compared with the corresponding free nucleon-nucleon values on
the basis of the predominance of quasi-elastic scattering processes.
Significant discrepancies have been observed in the polarization transfer
, which are presumably the result of the three-proton =
3/2 resonance.
The spin--parity of the resonance is estimated to be , and the
distribution is consistent with previous results obtained for the same reaction
at = 48.8 MeV.Comment: 4 figures, Accepted for publication in Physical Review
Study of nuclear correlation effects via 12C(p,n)12N(g.s.,1+) at 296 MeV
We report measurements of the cross section and a complete set of
polarization observables for the Gamow--Teller reaction at a bombarding
energy of 296 MeV.
The data are compared with distorted wave impulse approximation calculations
employing transition form factors normalized to reproduce the observed
beta-decay value.
The cross section is significantly under-predicted by the calculations at
momentum transfers 0.5 .
The discrepancy is partly resolved by considering the non-locality of the
nuclear mean field. However, the calculations still under-predict the cross
section at large momentum transfers of 1.6 .
We also performed calculations employing random phase approximation response
functions and found that the observed enhancement can be attributed in part to
pionic correlations in nuclei.Comment: 5 figures, submitted to Phys. Lett.
Pygmy dipole resonance in 208Pb
Scattering of protons of several hundred MeV is a promising new spectroscopic
tool for the study of electric dipole strength in nuclei. A case study of 208Pb
shows that at very forward angles J^pi = 1- states are strongly populated via
Coulomb excitation. A separation from nuclear excitation of other modes is
achieved by a multipole decomposition analysis of the experimental cross
sections based on theoretical angular distributions calculated within the
quasiparticle-phonon model. The B(E1) transition strength distribution is
extracted for excitation energies up to 9 MeV, i.e., in the region of the
so-called pygmy dipole resonance (PDR). The Coulomb-nuclear interference shows
sensitivity to the underlying structure of the E1 transitions, which allows for
the first time an experimental extraction of the electromagnetic transition
strength and the energy centroid of the PDR.Comment: submitted to Phys. Rev.
Complete electric dipole response and the neutron skin in 208Pb
A benchmark experiment on 208Pb shows that polarized proton inelastic
scattering at very forward angles including 0{\deg} is a powerful tool for
high-resolution studies of electric dipole (E1) and spin magnetic dipole (M1)
modes in nuclei over a broad excitation energy range to test up-to-date nuclear
models. The extracted E1 polarizability leads to a neutron skin thickness
r_skin = 0.156+0.025-0.021 fm in 208Pb derived within a mean-field model [Phys.
Rev. C 81, 051303 (2010)], thereby constraining the symmetry energy and its
density dependence, relevant to the description of neutron stars.Comment: 5 pages, 5 figures, revised mansucrip
Three Nucleon Force Effects in Intermediate Energy Deuteron Analyzing Powers for dp Elastic Scattering
A complete high precision set of deuteron analyzing powers for elastic
deuteron-proton () scattering at 250 MeV/nucleon (MeV/N) has been measured.
The new data are presented together with data from previous measurements at 70,
100, 135 and 200 MeV/N. They are compared with the results of three-nucleon
(3N) Faddeev calculations based on modern nucleon-nucleon (NN) potentials alone
or combined with two models of three nucleon forces (3NFs): the
Tucson-Melbourne 99 (TM99) and Urbana IX. At 250 MeV/N large discrepancies
between pure NN models and data, which are not resolved by including 3NFs, were
found at c.m.\ backward angles of for
almost all the deuteron analyzing powers. These discrepancies are quite similar
to those found for the cross section at the same energy. We found small
relativistic effects that cannot resolve the discrepancies with the data
indicating that other, short-ranged 3NFs are required to obtain a proper
description of the data.Comment: submitted to Phys. Rev.
Polarization transfer measurements for at 296 MeV and nuclear correlation effects
Differential cross sections and complete sets of polarization observables are
presented for the Gamow-Teller reaction at a bombarding energy of 296 MeV with momentum transfers
of 0.1 to . The polarization transfer observables are
used to deduce the spin-longitudinal cross section, , and spin-transverse
cross sections, and . The data are compared with calculations
based on the distorted wave impulse approximation (DWIA) using shell-model wave
functions. Significant differences between the experimental and theoretical
results are observed for all three spin-dependent at momentum transfers
of , suggesting the existence of nuclear
correlations beyond the shell model. We also performed DWIA calculations
employing random phase approximation (RPA) response functions and found that
the observed discrepancy is partly resolved by the pionic and rho-mesonic
correlation effects.Comment: accepted for publication in Phys. Rev.
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