84 research outputs found
Non-equilibrium emission of complex fragments from p+Au collisions at 2.5 GeV proton beam energy
Energy and angular dependence of double differential cross sections
d/ddE was measured for reactions induced by 2.5 GeV protons
on Au target with isotopic identification of light products (H, He, Li, Be, and
B) and with elemental identification of heavier intermediate mass fragments (C,
N, O, F, Ne, Na, Mg, and Al). It was found that two different reaction
mechanisms give comparable contributions to the cross sections. The
intranuclear cascade of nucleon-nucleon collisions followed by evaporation from
an equilibrated residuum describes low energy part of the energy distributions
whereas another reaction mechanism is responsible for high energy part of the
spectra of composite particles. Phenomenological model description of the
differential cross sections by isotropic emission from two moving sources led
to a very good description of all measured data. Values of the extracted
parameters of the emitting sources are compatible with the hypothesis claiming
that the high energy particles emerge from pre-equilibrium processes consisting
in a breakup of the target into three groups of nucleons; small, fast and hot
fireball of 8 nucleons, and two larger, excited prefragments, which
emits the light charged particles and intermediate mass fragments. The smaller
of them contains 20 nucleons and moves with velocity larger than the CM
velocity of the proton projectile and the target. The heavier prefragment
behaves similarly as the heavy residuum of the intranuclear cascade of
nucleon-nucleon collisions. %The mass and charge dependence of the total
production cross %sections was extracted from the above analysis for all
observed %reaction products. This dependence follows the power low behavior
%(A or Z)
Isospin dependence of the eta' meson production in nucleon--nucleon collisions
According to the quark model, the masses of eta and eta' mesons should be
almost equal. However, the empirical values of these masses differ by more than
the factor of two. Similarly, though the almost the same quark-antiquark
content, the total cross section for the creation of these mesons close to the
kinematical thresholds in the pp --> ppX reaction differs significantly. Using
the COSY-11 detection setup we intend to determine whether this difference will
also be so significant in the case of the production of these mesons in the
proton-neutron scattering. Additionally, the comparison of the pp --> pp eta'
and pn --> pn eta' total cross sections will allow to learn about the
production of the eta' meson in the channels of isospin I = 0 and I = 1 and to
investigate aspects of the gluonium component of the eta' meson.Comment: Presented at LEAP05: International conference on Low Energy
Antiproton Physics, Bonn - Juelich, Germany, May 16-22, 200
Eta and eta' mesons production at COSY-11
The low emittance and small momentum spread of the proton and deuteron beams
of the Cooler Synchrotron COSY combined with the high mass resolution of the
COSY-11 detection system permit to study the creation of mesons in the
nucleon-nucleon interaction down to the fraction of MeV with respect to the
kinematical threshold. At such small excess energies, the ejectiles possess low
relative momenta and are predominantly produced with the relative angular
momentum equal to zero. Taking advantage of these conditions we have performed
investigations aiming to determine the mechanism of the production of eta and
eta' mesons in the collision of hadrons as well as the hadronic interaction of
these mesons with nucleons and nuclei. In this proceedings we address the
ongoing studies of the spin and isospin dependence for the production of the
eta and eta' mesons in free and quasi-free nucleon-nucleon collisions. New
results on the spin observables for the vec(p)p --> pp eta reaction, combined
with the previously determined total cross section isospin dependence, reveal a
statistically significant indication that the excitation of the nucleon to the
S11(1535) resonance, the process which intermediates the production of the eta
meson in the nucleon-nucleon interactions, is predominantly due to the exchange
of the pi meson between the colliding nucleons.Comment: Invited talk at MESON 2006: 9th International Workshop on Meson
Production, Properties and Interactions, Cracow, Poland, 9-13 Jun 200
Isospin dependence of the eta prime meson production in nucleon-nucleon collisions
A comparison of the close-to-threshold total cross section for the eta prime
production in pp --> pp eta prime and pn --> pn eta prime reactions constitutes
a tool to investigate the eta prime meson structure and the reaction mechanism
in the channels of isospin I=0 and I=1 and may provide insight into the
flavour-singlet (perhaps also into gluonium) content of the eta prime meson. In
this contribution we present preliminary results of measurement of the
quasi-free production of the eta prime meson in the proton-neutron collisions
conducted using the COSY-11 facility.Comment: Presented at 10th International Workshop on Meson Production,
Properties and Interaction (MESON 2008), Cracow, Poland, 6 - 10 June 200
General thoughts to the Kaon pair production in the threshold region
Simple--minded thoughts about the cross sections for the reactions
pp-->ppK+K- and pp-->ppK0K0 are presented, which certainly do not account for
the complex coupled channel problem but rather provide some ideas into the
mutual reaction dynamics.Comment: Talk given at 9th International Workshop on Meson Production,
Properties and Interaction, Cracow, Poland, 9-13 June 2006. 3 pages, 2
figure
Associated strangeness production in pp collisions near threshold
Motivated by the ongoing discussion concerning the nature of the scalar
resonances f0(980) and a0(980), the COSY-11 collaboration has taken exclusive
data on the pp->ppK+K- reaction near the production threshold. A first total
cross section sigma=(1.80+-0.27+0.28-0.35)nb for the excess energy Q=17 MeV has
been determined. In contrary to the eta, omega and eta' single meson production
studies which clearly show the strong pp final state interaction (FSI), the
cross section values obtained at COSY-11 and DISTO can be both described by a
fit with a four-body phase space including the proton-proton final state
interaction as well as with one-meson exchange calculations neglecting FSI
effects. Therefore, one might think about a compensation of the strong pp
interaction through a pK- FSI effect or an additional degree of freedom caused
by the four-body final state. In the latter case, strong FSI effects can be
expected at Q-values very close to the K+K- production threshold. Such a
motivation triggered -- in combination with the investigation of the
kaon-Antikaon interaction being relevant to the structure of the f0(980) --
further measurements at the excess energies Q=10 and Q=28 MeV at COSY-11.Comment: 5 pages, 4 figures, Presented at X. International Conference On
Hadron Spectroscopy (Hadron 2003), Aschaffenburg, Germany, 31 Aug - 6 Sep
200
Dynamics of the near threshold eta meson production in proton-proton interaction
We present the results of measurements of the analysing power for the p(pol)p
--> pp eta reaction at the excess energies of Q=10 and 36 MeV, and interpret
these results within the framework of the meson exchange models. The determined
values of the analysing power at both excess energies are consistent with zero
implying that the eta meson is produced predominantly in s-wave.Comment: 3 pages, 3 figures, Presented at the Workshop on the physics of
excited nucleons (NSTAR 2007), 5-8 September 2007, Bonn, German
COSY-11: an experimental facility for studying meson production in free and quasi-free nucleon-nucleon collisions
The COSY-11 experimental setup is an internal facility installed at the
COoler SYnchrotron COSY in Juelich. It allows to investigate meson production
in free and quasi-free nucleon-nucleon collisions, eg. pp --> pp meson and pd
--> p_sp np meson reactions. Drift chambers and scintillators permit to measure
outgoing protons, separated in magnetic field of COSY-11 dipole. Neutrons are
registered in the neutron modular detector installed downstream the beam.
Recently, the experimental setup has been extended with spectator detector,
deuteron drift chamber and polarization monitoring system, and since then meson
production can be investigated also as a function of spin and isospin of
colliding nucleons.Comment: Presented at LEAP05: International conference on Low Energy
Antiproton Physics, Bonn - Juelich, Germany, May 16-22, 200
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