1,130 research outputs found
Meson-production experiments at COSY-Juelich
Selected results from experiments at COSY-Juelich are presented: an attempt
to measure the mass of the eta meson with high precision (ANKE facility), first
steps towards the detection of rare eta decays (WASA), and several measurements
of KKbar-pair production (ANKE, COSY-11, MOMO).Comment: Proceedings of QNP2009, Beijing, Sept. 2009; to be published in
Chinese Physics C. 6 pages, 5 figure
The energy dependence of the pp->K+ n Sigma+ reaction close to threshold
The production of the Sigma+ hyperon through the pp->K+nSigma+ reaction has
been investigated at four energies close to threshold, 1.826, 1.920, 1.958, and
2.020 GeV. At low energies, correlated K+pi+ pairs can only originate from
Sigma+ production so that their measurement allows the total cross section for
the reaction to be determined. The results obtained are completely consistent
with the values extracted from the study of the K+-proton correlation spectra
obtained in the same experiment. These spectra, as well as the inclusive K+
momentum distributions, also provide conservative upper limits on the Sigma+
production rates. The measurements show a Sigma+ production cross section that
varies roughly like phase space and, in particular, none of the three
experimental approaches used supports the anomalously high near-threshold
pp->K+ nSigma+ total cross section previously reported [T. Rozek et al., Phys.
Lett. B 643, 251 (2006)].Comment: Submitted to PR
New determination of the mass of the eta meson at COSY-ANKE
A value for the mass of the eta meson has been determined at the COSY-ANKE
facility through the measurement of a set of deuteron laboratory beam momenta
and associated 3He center-of-mass momenta in the d+p -> 3He+X reaction. The eta
was then identified by the missing-mass peak and the production threshold
determined. The individual beam momenta were fixed with a relative precision of
3 x 10^-5 for values around 3 GeV/c by using a polarized deuteron beam and
inducing an artificial depolarizing spin resonance, which occurs at a
well-defined frequency. The final-state momenta in the two-body d+p -> 3He+eta
reaction were investigated in detail by studying the size of the 3He momentum
ellipse with the forward detection system of the ANKE spectrometer. Final
alignment of the spectrometer for this high precision experiment was achieved
through a comprehensive study of the 3He final-state momenta as a function of
the center-of-mass angles, taking advantage of the full geometrical acceptance.
The value obtained for the mass, m(eta)=(547.873 +- 0.005(stat) +- 0.027(syst))
MeV/c^2, is consistent and competitive with other recent measurements, in which
the meson was detected through its decay products.Comment: 11 pages, 11 figures, 3 tables, published versio
High precision beam momentum determination in a synchrotron using a spin resonance method
In order to measure the mass of the eta meson with high accuracy using the
d+p -> 3He+eta reaction, the momentum of the circulating deuteron beam in the
Cooler Synchrotron COSY of the Forschungszentrum Juelich has to be determined
with unprecedented precision. This has been achieved by studying the spin
dynamics of the polarized deuteron beam. By depolarizing the beam through the
use of an artificially induced spin resonance, it was possible to evaluate its
momentum p with a precision of dp/p < 10-4 for a momentum of roughly 3 GeV/c.
Different possible sources of error in the application of the spin resonance
method are discussed in detail and its possible use during a standard
experiment is considered.Comment: 10 pages, 6 figures, 2 tables, published versio
The production of K+K- pairs in proton-proton collisions at 2.83 GeV
Differential and total cross sections for the pp -> ppK+K- reaction have been
measured at a proton beam energy of 2.83 GeV using the COSY-ANKE magnetic
spectrometer. Detailed model descriptions fitted to a variety of
one-dimensional distributions permit the separation of the pp -> pp phi cross
section from that of non-phi production. The differential spectra show that
higher partial waves represent the majority of the pp -> pp phi total cross
section at an excess energy of 76 MeV, whose energy dependence would then seem
to require some s-wave phi-p enhancement near threshold. The non-phi data can
be described in terms of the combined effects of two-body final state
interactions using the same effective scattering parameters determined from
lower energy data.Comment: 12 pages, 12 figures, 3 table
Monitoring of the accelerator beam distributions for internal target facilities
We describe a direct method for monitoring the geometrical dimensions of a
synchrotron beam at the target position for internal target installations. The
method allows for the observation of the proton beam size as well as the
position of the beam relative to the target. As a first demonstration of the
technique, we present results obtained by means of the COSY-11 detection system
installed at the cooler synchrotron COSY. The influence of the stochastic
cooling on the COSY proton beam dimensions is also investigated.Comment: 7 pages, 8 figures, Submitted to Nucl. Inst. & Meth.
Production of the 1S0 diproton in the pp -> pp pi0 reaction at 0.8 GeV
The pp -> pp pi0 differential cross section has been measured with the ANKE
spectrometer at COSY-Juelich for pion cms angles between 0 and 15.4 degrees at
a proton beam energy of 0.8 GeV. The selection of diproton pairs with an
excitation energy E_{pp} < 3 MeV ensures that the final pp system is dominantly
in the spin-singlet 1S0 state. The kinematics are therefore very similar to
those of pp -> d pi+ but with different spin and isospin transitions. The
results will thus provide a crucial extra test of pion production models in
nucleon-nucleon collisions.
The cross sections, which are over two orders of magnitude smaller than those
of pp -> d pi+, show a forward dip, even stronger than that seen at lower
energies. This behaviour is well reproduced in a theoretical model that
includes P-wave Delta-N states.Comment: 10 pages, 5 eps figures, prepared using elsart.cl
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