2 research outputs found
Insensitivity of the elastic proton-nucleus reaction to the neutron radius of 208Pb
The sensitivity--or rather insensitivity--of the elastic proton-nucleus
reaction to the neutron radius of 208Pb is investigated using a
non-relativistic impulse-approximation approach. The energy region (Tlab=500
MeV and Tlab=800 MeV) is selected so that the impulse approximation may be
safely assumed. Therefore, only free nucleon-nucleon scattering data are used
as input for the optical potential. Further, the optical potential includes
proton and neutron ground-state densities that are generated from
accurately-calibrated models. Even so, these models yield a wide range of
values (from 0.13 fm to 0.28 fm) for the poorly known neutron skin thickness in
208Pb. An excellent description of the experimental cross section is obtained
with all neutron densities. We have invoked analytic insights developed within
the eikonal approximation to understand the insensitivity of the differential
cross section to the various neutron densities. As the diffractive oscillations
of the cross sections are controlled by the matter radius of the nucleus, the
large spread in the neutron skin among the various models gets diluted into a
mere 1.5% difference in the matter radius. This renders ineffective the elastic
reaction as a precision tool for the measurement of neutron radii.Comment: 17 pages with 5 figure