253 research outputs found
The nn quasi-free nd breakup cross section: discrepancies to theory and implications on the 1S0 nn force
Large discrepancies between quasi-free neutron-neutron (nn) cross section
data from neutron-deuteron (nd) breakup and theoretical predictions based on
standard nucleon-nucleon (NN) and three-nucleon (3N) forces are pointed out.
The nn 1S0 interaction is shown to be dominant in that configuration and has to
be increase to bring theory and data into agreement. Using the next-to-leading
order (NLO) 1S0 interaction of chiral perturbation theory (chiPT) we
demonstrate that the nn QFS cross section only slightly depends on changes of
the nn scattering length but is very sensitive to variations of the effective
range parameter. In order to account for the reported discrepancies one must
decrease the nn effective range parameter by about 12 % from its value implied
by 19charge symmetry and charge independence of nuclear forces.Comment: 19 pages, 11 figure
Numerical investigations of the three-dimensional proton-proton screened Coulomb t-matrix
We demonstrate behaviour of the momentum space screened Coulomb t-matrix,
obtained by a numerical solution of the three-dimensional Lippmann-Schwinger
equation. Examples are given for different types of screening. They prove that
it is possible to obtain numerically a reliable three-dimensional screened
Coulomb t-matrix, what is important in view of its application in few-body
calculations.Comment: 23 pages, 2 tables, 13 figures in 65 eps file
Relativistic effects in neutron-deuteron elastic scattering
We solved the three-nucleon Faddeev equation including relativistic features
such as relativistic kinematics, boost effects and Wigner spin rotations. As
dynamical input a relativistic nucleon-nucleon interaction exactly on-shell
equivalent to the AV18 potential has been used. The effects of Wigner rotations
for elastic scattering observables were found to be small. The boost effects
are significant at higher energies.They diminish the transition matrix elements
at higher energies and lead in spite of the increased relativistic phase-space
factor as compared to the nonrelativistic one to rather small effects in the
cross section, which are mostly restricted to the backward angles.Comment: 27 pages, 5 Postscript figure
On the usefulness of the spectral function concept
The usefulness of the spectral function S in the process 3He(e,e'N) has been
investigated in a kinematical regime constrained by the conditions that the
three-nucleon center-of-mass energy is less than 150 MeV and the magnitude of
the three-momentum transfer smaller than 600 MeV/c. Results based on a full
treatment of the final state interaction are compared to the spectral function
approximation. In the case of proton knockout in the direction of the photon
kinematical conditions have been identified where both response functions, RL
and RT, can be well approximated by S. These conditions occur for certain low
missing momenta and missing energies but not in all cases. So care is required.
In case of neutron knockout only RT is a candidate for an approximate treatment
by S. In the case of RL the concept of using S is not valid in the studied
kinematical regime. This does not exclude the possibility that beyond that
regime it might be useful. Possible applications using S for the extraction of
electromagnetic form factors of the nucleons are pointed out.Comment: 27 pages, 25 fugure
Three-Body Elastic and Inelastic Scattering at Intermediate Energies
The Faddeev equation for three-body scattering at arbitrary energies is
formulated in momentum space and directly solved in terms of momentum vectors
without employing a partial wave decomposition. For identical bosons this
results in a three-dimensional integral equation in five variables, magnitudes
of relative momenta and angles. The cross sections for both elastic and breakup
processes in the intermediate energy range up to about 1 GeV are calculated
based on a Malfliet-Tjon type potential, and the convergence of the multiple
scattering series is investigated.Comment: Talk at the 18th International IUPAP Conference on Few-Body Problems
in Physics, Aug. 21-26, 2006, Santos, Brazi
Proton polarizations in polarized 3He studied with the \vec{3He} (\vec{e},e' p)d and \vec{3He} (\vec{e},e' p)pn processes
We study within the Faddeev framework the \vec{3He} (\vec{e},e' p)d as well
as the \vec{3He} (\vec{e},e' p)pn and \vec{3He} (\vec{e},e' n)pp reactions in
order to extract information on the proton and neutron polarization in
polarized 3He. We achieve clear analytical insight for simplified dynamical
assumptions and define conditions for experimental access to important 3He
properties. In addition we point to the possibility to measure the
electromagnetic proton form factors in the process \vec{3He} (\vec{e},e' p)d
which would test the dynamical picture and put limits on medium corrections of
the form factors.Comment: 38 pages, 22 figure
Theoretical uncertainties of the elastic nucleon-deuteron scattering observables
Theoretical uncertainties of various types are discussed for the
nucleon-deuteron elastic scattering observables at the incoming nucleon
laboratory energies up to 200 MeV. We are especially interested in the
statistical errors arising from uncertainties of parameters of a
nucleon-nucleon interaction. The obtained uncertainties of the differential
cross section and numerous scattering observables are in general small, grow
with the reaction energy and amount up to a few percent at 200 MeV. We compare
these uncertainties with the other types of theoretical errors like truncation
errors, numerical uncertainties and uncertainties arising from using the
various models of nuclear interaction. We find the latter ones to be dominant
source of uncertainties of modern predictions for the three-nucleon scattering
observables. To perform above mentioned studies we use the One-Pion-Exchange
Gaussian potential derived by the Granada group, for which the covariance
matrix of its parameters is known, and solve the Faddeev equation for the
nucleon-deuteron elastic scattering. Thus beside studying theoretical
uncertainties we also show a description of the nucleon-deuteron elastic
scattering data by the One-Pion-Exchange Gaussian model and compare it with
results obtained with other nucleon-nucleon potentials, including chiral
NLO forces from the Bochum-Bonn and Moscow(Idaho)-Salamanca groups. In this
way we confirm the usefulness and high quality of the One-Pion-Exchange
Gaussian force.Comment: 23 pages, 15 figures in 64 eps file
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