608 research outputs found
On Quasibound N* Nuclei
The possibility for the existence of unstable bound states of the S11 nucleon
resonance N(1535) and nuclei is investigated. These quasibound states are
speculated to be closely related to the existence of the quasibound states of
the eta mesons and nuclei. Within a simple model for the N N interaction
involving a pion and eta meson exchange, N-nucleus potentials for N*-He
and N*-Mg are evaluated and found to be of a Woods-Saxon like form which
supports two to three bound states. In case of N*-He, one state bound by
only a few keV and another by 4 MeV is found. The results are however quite
sensitive to the N N and N N vertex parameters. A rough
estimate of the width of these states, based on the mean free path of the
exchanged mesons in the nuclei leads to very broad states with 80
and 110 MeV for N*-He and N*-Mg respectively.Comment: Presented at the Jagiellonian Symposium on Fundamental and Applied
Subatomic Physics, Cracow, Poland, June 2015; to be published in Acta Physica
Polonica B (2016
Possible eta-mesic 3He states within the finite rank approximation
We extend the method of time delay proposed by Eisenbud and Wigner, to search
for unstable states formed by eta mesons and the 3He nucleus. Using few body
equations to describe eta-3He elastic scattering, we predict resonances and
unstable bound states within different models of the eta-N interaction. The
eta-3He states predicted within this novel approach are in agreement with the
recent claim of the evidence of eta-mesic 3He made by the TAPS collaboration.Comment: 10 pages LaTex, 3 figure
Small eta-N scattering lengths favour eta-d and eta-alpha states
Unstable states of the eta meson and the 3He nucleus predicted using the time
delay method were found to be in agreement with a recent claim of eta-mesic 3He
states made by the TAPS collaboration. Here, we extend this method to a
speculative study of the unstable states occurring in the eta-d and eta-4He
elastic scattering. The T-matrix for eta-4He scattering is evaluated within the
Finite Rank Approximation (FRA) of few body equations. For the evaluation of
time delay in the eta-d case, we use a parameterization of an existing Faddeev
calculation and compare the results with those obtained from FRA. With an eta-N
scattering length, fm, we find an eta-d unstable
bound state around -16 MeV, within the Faddeev calculation. A similar state
within the FRA is found for a low value of , namely, fm. The existence of an eta-4He unstable bound state close to
threshold is hinted by fm, but is ruled out by
large scattering lengths.Comment: 21 pages, LaTex, 7 Figure
Comment on "Hadronic He production near threshold"
Measurements of the differential and total cross sections for the He reaction at five energies were recently reported [Phys. Rev. C
{\bf 75}, 014004 (2007)] and comparisons with theoretical models were made. We
point out that these comparisons involved a model based on ad hoc assumptions
and hence the conclusions regarding the reaction mechanism as well as the role
of the higher partial waves drawn in the above work are misleading. Revised
conclusions based on better model calculations are presented
Evidence of Pentaquark States from K+ N Scattering Data?
Motivated by the recent experimental evidence of the exotic B = S = +1
baryonic state Theta(1540), we examine the older existing data on K+ N elastic
scattering through the time delay method. We find positive peaks in time delay
around 1.545 and 1.6 GeV in the D03 and P01 partial waves of K+ N scattering
respectively, in agreement with experiments. We also find an indication of the
J=3/2 Theta* spin-orbit partner to the Theta, in the P03 partial wave at 1.6
GeV. We discuss the pros and contras of these findings in support of the
interpretation of these peaks as possible exotics.Comment: 10 pages, 4 figure
A study of the reaction
A study of the reaction in the energy range where the
recent data from Uppsala are available, is done in the two-step model of
production including the final state interaction. The final state
interaction is incorporated through the solution of the Lippmann Schwinger
equation using an elastic scattering matrix element, ,
which is required to be half off-shell. It is written in a factorized form,
with an off-shell form factor multiplying an on-shell part given by an
effective range expansion up to the fourth power in momentum. The parameters of
this expansion have been taken from an existing recent relativistic Faddeev
equation solution for the system corresponding to different
scattering amplitudes. Calculations have also been done using few body
equations within a finite rank approximation (FRA) to generate . The final state interaction is included in the spirit of the
Watson-Migdal prescription by multiplying the matrix element by the inverse of
the Jost function. The interaction is found to be dominant in the
region of small invariant mass, . The interaction
enhances the cross section in the whole region of , but is larger
for large . We find nearly isotropic angular distributions of the
proton and the deuteron in the final state. All the above observations are in
agreement with data. The production mechanism for the entire range of the
existing data on the reaction seems to be dominated by the
two-step model of production.Comment: 22 pages, 12 figures, accepted for publication in Phys. Rev.
- …