1,641 research outputs found
Inclusive K^+ meson production in proton-nucleus interactions
The production of K^+ mesons in pA (A = D, C, Cu, Ag, Au) collisions has been
investigated at the COoler SYnchrotron COSY-J\"ulich for beam energies T_p =
1.0 - 2.3 GeV. Double differential inclusive pC cross sections at forward
angles theta < 12 degrees as well as the target-mass dependence of the K^+
momentum spectra have been measured with the ANKE spectrometer. Far below the
free NN threshold at T_{NN}=1.58 GeV the spectra reveal a high degree of
collectivity in the target nucleus. From the target-mass dependence of the
cross sections at higher energies, the repulsive in-medium potential of K^+
mesons can be deduced. Using pN cross-section parameterisations from literature
and our measured pD data we derive a cross-section ratio of sigma(pn -> K^+ X)
/ sigma(pp -> K^+ X) ~ (3-4).Comment: Accepted for publication in EPJ A; 17 pages, 10 figures, 11 table
High density cluster jet target for storage ring experiments
The design and performance of a newly developed cluster jet target
installation for hadron physics experiments are presented which, for the first
time, is able to generate a hydrogen cluster jet beam with a target thickness
of above at a distance of two metres behind the
cluster jet nozzle. The properties of the cluster beam and of individual
clusters themselves are studied at this installation. Special emphasis is
placed on measurements of the target beam density as a function of the relevant
parameters as well as on the cluster beam profiles. By means of a
time-of-flight setup, measurements of the velocity of single clusters and
velocity distributions were possible. The complete installation, which meets
the requirements of future internal fixed target experiments at storage rings,
and the results of the systematic studies on hydrogen cluster jets are
presented and discussed.Comment: 10 pages, 18 figure
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
Spectator detection for the measurement of proton neutron interactions at ANKE
A telescope of three silicon detectors has been installed close to the
internal target position of the ANKE spectrometer, which is situated inside the
ultra-high vacuum of the COSY-Juelich light-ion storage ring. The detection and
identification of slow protons and deuterons emerging from a deuterium
cluster-jet target thus becomes feasible. A good measurement of the energy and
angle of such a spectator proton (p_sp) allows one to identify a reaction as
having taken place on the neutron in the target and then to determine the
kinematical variables of the ion-neutron system on an event-by-event basis over
a range of c.m. energies.
The system has been successfully tested under laboratory conditions. By
measuring the spectator proton in the p d to p_sp d pi^0 reaction in
coincidence with a fast deuteron in the ANKE Forward Detector, values of the p
n to d pi^0 total cross-section have been deduced. Further applications of the
telescope include the determination of the luminosity and beam polarisation
which are required for several experiments.Comment: 16 pages, 9 figure
The fundamental problem of command : plan and compliance in a partially centralised economy
When a principal gives an order to an agent and advances resources for its implementation, the temptations for the agent to shirk or steal from the principal rather than comply constitute the fundamental problem of command. Historically, partially centralised command economies enforced compliance in various ways, assisted by nesting the fundamental problem of exchange within that of command. The Soviet economy provides some relevant data. The Soviet command system combined several enforcement mechanisms in an equilibrium that shifted as agents learned and each mechanism's comparative costs and benefits changed. When the conditions for an equilibrium disappeared, the system collapsed.Comparative Economic Studies (2005) 47, 296–314. doi:10.1057/palgrave.ces.810011
Combined Analysis of Near-Threshold Production of omega and phi Mesons in Nucleon-Nucleon Collisions within an Effective Meson-Nucleon Model
Vector meson () production in near-threshold elementary
nucleon-nucleon collisions , and is studied
within an effective meson-nucleon theory. It is shown that a set of effective
parameters can be established to describe fairly well the available
experimental data of angular distributions and the energy dependence of the
total cross sections without explicit implementation of the Okubo-Zweig-Iisuka
rule violation. Isospin effects are considered in detail and compared with
experimental data whenever available
Primary accumulation in the Soviet transition
The Soviet background to the idea of primary socialist accumulation is presented. The mobilisation of labour power and of products into public sector investment from outside are shown to have been the two original forms of the concept. In Soviet primary accumulation the mobilisation of labour power was apparently more decisive than the mobilisation of products. The primary accumulation process had both intended and unintended results. Intended results included bringing most of the economy into the public sector, and industrialisation of the economy as a whole. Unintended results included substantial economic losses, and the proliferation of coercive institutions damaging to attainment of the ultimate goal - the building of a communist society
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
Lineshape of the Lambda(1405) Hyperon Measured Through its Sigma0 pion0 Decay
The pp -> p K+ Y0 reaction has been studied for hyperon masses m(Y0)<1540
MeV/c2 at COSY-Juelich by using a 3.65 GeV/c circulating proton beam incident
on an internal hydrogen target. Final states comprising two protons, one
positively charged kaon and one negatively charged pion have been identified
with the ANKE spectrometer. Such configurations are sensitive to the production
of the ground state Lambda and Sigma0 hyperons as well as the Sigma0(1385) and
Lambda(1405) resonances. Applying invariant- and missing-mass techniques, the
two overlapping excited states could be well separated, though with limited
statistics. The shape and position of the Lambda(1405) distribution,
reconstructed cleanly in the Sigma0 pion0 channel, are similar to those found
from other decay modes and there is no obvious mass shift. This finding
constitutes a challenging test for models that predict Lambda(1405) to be a
two-state resonance.Comment: 10 pages, 4 figures, accepted for publication in Phys. Lett.
Kaon pair production in proton-nucleus collisions at 2.83 GeV kinetic energy
The production of non-phi K+K- pairs by protons of 2.83 GeV kinetic energy on
C, Cu, Ag, and Au targets has been investigated using the COSY-ANKE magnetic
spectrometer. The K- momentum dependence of the differential cross section has
been measured at small angles over the 0.2--0.9 GeV/c range. The comparison of
the data with detailed model calculations indicates an attractive K- -nucleus
potential of about -60 MeV at normal nuclear matter density at a mean momentum
of 0.5 GeV/c. However, this approach has difficulty in reproducing the
smallness of the observed cross sections at low K- momenta.Comment: 7 pages, 5 figures, 1 tabl
- …