169 research outputs found
On the close to threshold meson production in neutron-neutron collisions
A method of measuring the close to threshold meson production in
neutron-neutron collisions is described where the momenta of the colliding
neutrons can be determined with the accuracy obtainable for the proton-proton
reaction. The technique is based on the double quasi-free nn --> nn X^0
reaction, where deuterons are used as a source of neutronsComment: 6 pages, 2 figures, to be published in Phys. Lett.
Eta physics at threshold
The production of eta and eta-prime mesons in elementary nucleon-nucleon
collisions has been investigated at the synchrotrons CELSIUS, COSY and SATURNE.
The magnitude and energy dependence of the total cross section as well as the
occupation distribution of the phase space serve as observables for
investigating the mechanisms underlying the production processes and the
interaction of mesons with nucleons. The precise data on the eta and eta-prime
creation via the pp --> pp eta(eta-prime) reactions allowed to settle the
general features of the eta and eta-prime meson production and revealed the
sensitivity of the mentioned observables to the nucleon-nucleon-meson final
state interaction. The particular production properties, like for example the
determination of the dominating exchange processes which lead to the excitation
of the S_11 nucleon isobar in the case of eta creation, must be established by
confrontation with other observables. The present status of this investigation
with an emphasis on the results of the COSY-11 collaboration is briefly
presented. The available data are interpreted in view of the production
mechanism and the meson-nucleon interaction.Comment: 3 pages, 3 figures, Presented at Conference on Quarks and Nuclear
Physics (QNP 2002), Julich, Germany, 9-14 Jun 200
Eta Meson Production in NN Collisions
Eta meson production in both proton-proton and proton-neutron collisions is
investigated within a relativistic meson exchange model of hadronic
interactions. It is found that the available cross section data can be
described equally well by either the vector or pseudoscalar meson exchange
mechanism for exciting the S_{11}(1535) resonance. It is shown that the
analyzing power data can potentially be very useful in distinguishing these two
scenarios for the excitaion of the S_{11}(1535) resonance.Comment: Revtex, 35 pages, 8 figure
Near-Threshold eta Meson Production in Proton-Proton Collisions
The production of eta mesons has been measured in the proton-proton
interaction close to the reaction threshold using the COSY-11 internal facility
at the cooler synchrotron COSY. Total cross sections were determined for eight
different excess energies in the range from 0.5 MeV to 5.4 MeV. The energy
dependence of the total cross section is well described by the available
phase-space volume weighted by FSI factors for the proton-proton and proton-eta
pairs.Comment: 9 pages, 1 table, 5 figure
eta d scattering in the region of the S11 resonance
We have studied the reaction eta d -> eta d close to threshold within a
nonrelativistic three-body formalism. We considered several eta N and NN
models, in particular potentials with separable form, fitted to the low-energy
eta N and NN data to represent the two-body interactions. We found that with
realistic two-body interactions a quasibound state does not exist in this
system, although there is an enhancement of the cross section by one order of
magnitude, in the region near threshold, which is a genuine three-body effect
not predicted within the impulse approximation.Comment: 18 pages Revtex, 2 figure
Incoherent Photoproduction of -mesons from the Deuteron near Threshold
Incoherent photoproduction of the -meson on the deuteron is studied for
photon energies from threshold to 800 MeV. The dominant contribution, the
N-N amplitude, is described within an isobar model. The final
state interaction derived from the CD-Bonn potential is included and found to
be important for the description of the production cross section close to
threshold. Possible effects from the final state interaction are
discussed.Comment: 11 pages, revtex, including 6 figure
Phenomenology of pp->pp eta reaction close to threshold
The recent high statistics measurement of the pp -> pp eta reaction at an
excess energy Q=15.5 MeV has been analysed by means of partial wave
decomposition of the cross section. Guided by the dominance of the final state
1S0 pp interaction (FSI), we keep only terms involving the FSI enhancement
factor. The measured p-p and p-eta effective mass spectra can be well
reproduced by lifting the standard on-shell approximation in the enhancement
factor and by allowing for a linear energy dependence in the leading 3P0->1S0,s
partial wave amplitude. Higher partial waves seem to play only a marginal role
Comparison of the Near-Threshold Production of eta- and K-Mesons in Proton-Proton Collisions
The pp -> pp eta and pp -> pLambda K^+ reactions near threshold are dominated
by the first and second S_11 resonance respectively. It is shown that a
one-pion-exchange model exciting these isobars reproduces well the ratio of the
production cross sections. The consequences for this and other channels are
discussed.Comment: 10 pages, LaTeX2e, 1 eps-figur
S-wave eta'-proton FSI; phenomenological analysis of near-threshold production of pi0, eta, and eta' mesons in proton-proton collisions
We describe a novel technique for comparing total cross sections for the
reactions pp --> pp pi(0), pp --> pp eta, and pp --> pp eta' close to
threshold. The initial and final state proton-proton interactions are factored
out of the total cross section, and the dependence of this reduced cross
section on the volume of phase space is discussed. Different models of the
proton-proton interaction are compared. We argue that the scattering length of
the S-wave eta'-proton interaction is of the order of 0.1 fm.Comment: 10 pages, 5 figure
Higher Partial Waves in p+p->p+p+eta near Threshold
Exclusive measurements of the production of eta mesons in the p+p->p+p+eta
reaction have been carried out at excess energies of 16 and 37 MeV above
threshold. The deviations from phase space are dominated by the proton-proton
final state interaction and this influences particularly the energy
distribution of the eta meson. However, evidence is also presented at the
higher energy for the existence of an anisotropy in the angular distributions
of the eta meson and also of the final proton-proton pair, probably to be
associated with D-waves in this system interfering with the dominant S-wave
term. The sign of the eta angular anisotropy suggests that rho-exchange is
important for this reaction.Comment: 16 pages, LaTeX2e, 3 EPS Figures, Updated version, Accepted for
publication in Phys. Lett.
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