217 research outputs found
Isotopic Production Cross Sections in Proton-Nucleus Collisions at 200 MeV
Intermediate mass fragments (IMF) from the interaction of Al,
Co and Au with 200 MeV protons were measured in an angular range
from 20 degree to 120 degree in the laboratory system. The fragments, ranging
from isotopes of helium up to isotopes of carbon, were isotopically resolved.
Double differential cross sections, energy differential cross sections and
total cross sections were extracted.Comment: accepted by Phys. Rev.
Search for He-eta bound states with the WASA-at-COSY facility
The existence of eta-mesic nuclei in which the eta meson is bound in a
nucleus by means of the strong interaction was postulated already in 1986,
albeit not yet confirmed it by experiment. The discovery of this new kind of an
exotic nuclear matter would be very important as it might allow for a better
understanding of the eta meson structure and its interaction with nucleons. The
search for eta-mesic helium 4He-eta is carried out with high statistics and
high acceptance with the WASA detector, installed at the cooler synchrotron
COSY of the Research Center Juelich. The search is conducted via the
measurement of the excitation function for selected decay channels of the
4He-eta system. In the experiment, performed in November 2010, two reactions
dd->(4He-eta)bs ->3He p pi- and dd->(4He-eta)bs ->3He p pi0 were measured with
a beam momentum ramped from 2.127GeV/c to 2.422GeV/c. The report includes the
description of the experimental method and status of the measurement.Comment: Presented at the Erice School on Nuclear Physics 2011. 5 pages, 3
figure
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)
A method to disentangle single- and multi-meson production in missing mass spectra from quasi-free pn --> pn X reactions
The separation of contributions from multi- and single-meson production in
the missing mass spectrum of the quasi-free pn --> pnX reaction constitutes
a~challenging task when the reaction is studied close to threshold. This is
especially true if the resolution of the mass determination is comparable with
the excess energy and if the investigated signal appears close to the
kinematical limit. In this article we outline a method which permits the
extraction of the signal originating from the creation of a single meson
without the necessity of conducting model-dependent simulations. For the pd -->
pnXp(spectator) reactions, the method allows one to combine events
corresponding to multi-meson production at various excess energies with respect
to the pn --> pn meson process, and hence leads to an increase of the
statistics needed for the determination of the shape of the multi-meson
background.
As an example of the application of the method, we demonstrate that the
evaluation of the data from the pd --> pnXp(sp) process according to the
described technique enables one to extract a signal of the pn --> pn eta
reaction whose shape is consistent with expectations, supporting the
correctness and usefulness of the method introduced.Comment: 14 pages, 10 figure
Upper limits for a narrow resonance in the reaction p + p -> K^+ + (Lambda p)
The reaction pp -> K^+ + (Lambda p) has been measured at T_p = 1.953 GeV and
\Theta = 0 deg with a high missing mass resolution in order to study the Lambda
p final state interaction. Narrow S = -1 resonances predicted by bag model
calculations are not visible in the missing mass spectrum. Small structures
observed in a previous experiment are not confirmed. Upper limits for the
production cross section of a narrow resonance are deduced for missing masses
between 2058 and 2105 MeV/c^2.Comment: 8 pages, 5 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.
Detailed comparison of the pp -> \pi^+pn and pp -> \pi^+d reactions at 951 MeV
The positively charged pions produced in proton-proton collisions at a beam
momentum of 1640 MeV/c were measured in the forward direction with a high
resolution magnetic spectrograph. The missing mass distribution shows the bound
state (deuteron) clearly separated from the continuum. Despite the very
good resolution, there is no evidence for any significant production of the
system in the spin-singlet state. However, the cross section ratio is about twice as large as
that predicted from -wave final-state-interaction theory and it is suggested
that this is due to -state effects in the system.Comment: 8 pages, 3 figure
MesonNet 2013 International Workshop. Mini-proceedings
The mini-proceedings of the MesonNet 2013 International Workshop held in
Prague from June 17th to 19th, 2013, are presented. MesonNet is a research
network within EU HadronPhysics3 project (1/2012 -- 12/2014). The web page of
the conference, which contains all talks, can be found at
http://ipnp.mff.cuni.cz/mesonnet13Comment: 106 pages, 53 contributions. Mini-proceedings of the MesonNet 2013
International Workshop. Editors: K. Kampf, A. Kupsc, and P. Masjua
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