126 research outputs found
Courbes d'excitation des réactions 18O(p,p1γ) 18O* et 18O(p,α1,2,3γ)15N* de 3,2 à 5,4 MeV
Les courbes d'excitation des réactions 18O(p, p1) 18O* et 18O(p, α1,2,3)15N* ont été mesurées pour les énergies incidentes de 3,2 à 5,4 MeV. Les courbes montrent, pour certaines énergies, des anticorrélations entre les voies de sortie proton et alpha. Si cet effet peut être attribué à la conservation du spin isobarique dans les réactions, il détermine le spin isobarique de quelques états excités du noyau composé 19F
SEARCH FOR NARROW ISOVECTOR DIBARYONS CLOSE TO LOW MASSES THRESHOLD
For masses larger than 2 MN + Mπ, narrow peaks in two proton invariant (missing) masses spectra : Mpp (Mx) are now well established. The existence of such narrow peaks is not so unquestionable below 2 MN + Mπ. Tensor analyzing power T20 of the invariant mass Mpp has been studied using the p ([MATH], pp) reaction. Depending on the assumption done for background substraction -a hole or an oscillation may appear at Mpp = 1941 MeV. Additional data are under analysis and will improve the statistics
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
Threshold production in nucleon-nucleon collisions
We analyze production in nucleon-nucleon collisions near threshold
in the framework of a general model independent formalism, which can be applied
to any reaction , where , , or . Such
reactions show large isotopic effects: a large difference for - and
-collisions, which is due to the different spin structure of the
corresponding matrix elements. The analysis of the spin structure and of the
polarization observables is based on symmetry properties of the strong
interaction. Using existing experimental data on the different decays of
meson, we suggest a model for , based on
channel -exchanges. We predict polarization phenomena for the
-reaction and the ratio of cross sections for and
-collisions. For the processes we apply two
different approaches: vector meson exchange and local four-particle
interaction. In both cases we find larger -production in
-collisions, with respect to -collisions.Comment: 17 pages, 6 figure
Near-Threshold Production of omega Mesons in the pp -> pp omega Reaction
The total cross section for omega production in the pp -> pp omega reaction
has been measured at five c.m. excess energies from 3.8 to 30 MeV. The energy
dependence is easily understood in terms of a strong proton-proton final state
interaction combined with a smearing over the width of the state. The ratio of
near-threshold phi and omega production is consistent with the predictions of a
one-pion-exchange model and the degree of violation of the OZI rule is similar
to that found in the pi-p -> n omega/phi reactions.Comment: Report in LaTeX2e. 12 pages with 2 eps figure
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
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.
Energy Dependence of the Near-Threshold Total Cross-Section for the pp --> pp eta' Reaction
Total cross sections for the pp --> pp eta' reaction have been measured in
the excess energy range from Q = 1.53 MeV to Q = 23.64 MeV. The experiment has
been performed at the internal installation COSY-11 using a stochastically
cooled proton beam of the COoler SYnchrotron COSY and a hydrogen cluster
target. The determined energy dependence of the total cross section weakens the
hypothesis of the S-wave repulsive interaction between the eta' meson and the
proton. New data agree well with predictions based on the phase-space
distribution modified by the proton-proton final-state-interaction (FSI) only.Comment: 12 pages, 1 table, 4 figure
Production of Mesons in the Reaction at 3.67 GeV/c
The ratio of the total exclusive production cross sections for
and mesons has been measured in the reaction at
GeV/c. The observed ratio is
from which the exclusive
meson production cross section is determined to be
. Differential cross section
distributions have been measured. Their shape is consistent with isotropic
meson production.Comment: 14 pages, 5 figures, accepted by Phys.Lett.
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