302 research outputs found
A phenomenological analysis of antiproton interactions at low energies
We present an optical potential analysis of the antiproton-proton
interactions at low energies. Our optical potential is purely phenomenological,
and has been parametrized on data recently obtained by the Obelix Collaboration
at momenta below 180 MeV/c. It reasonably fits annihilation and elastic data
below 600 MeV/c, and allows us for an evaluation of the elastic cross section
and rho-parameter down to zero kinetic energy. Moreover we show that the
mechanism that depresses antiproton-nucleus annihilation cross sections at low
energies is present in antiproton-proton interactions too.Comment: 10 pages, 4 figure
On the muon neutrino mass
During the runs of the PS 179 experiment at LEAR of CERN, we photographed an
event of antiproton-Ne absorption, with a complete pi+ -> mu+ ->e+ chain. From
the vertex of the reaction a very slow energy pi+ was emitted. The pi+ decays
into a mu+ and subsequently the mu+ decays into a positron. At the first decay
vertex a muon neutrino was emitted and at the second decay vertex an electron
neutrino and a muon antineutrino. Measuring the pion and muon tracks and
applying the momentum and energy conservation and using a classical statistical
interval estimator, we obtained an experimental upper limit for the muon
neutrino mass: m_nu < 2.2 MeV at a 90% confidence level. A statistical analysis
has been performed of the factors contributing to the square value of the
neutrino mass limit.Comment: 18 pages, 5 eps figure
K Meson Production in the Proton-Proton Reaction at 3.67 GeV/c
The total cross section of the reaction has been determined
for proton--proton reactions with . This represents the
first cross section measurement of the channel near
threshold, and is equivalent to the inclusive cross section at
this beam momentum. The cross section determined at this beam momentum is about
a factor 20 lower than that for inclusive meson production at
the same CM energy above the corresponding threshold. This large difference in
the and meson inclusive production cross sections in proton-proton
reactions is in strong contrast to cross sections measured in sub-threshold
heavy ion collisions, which are similar in magnitude at the same energy per
nucleon below the respective thresholds.Comment: 12 pages, 3 figures Phys. Lett. B in prin
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.
Measurements of the reaction of antiproton annihilation at rest at three hydrogen target densities
The proton-antiproton annihilation at rest into the final state
was measured for three different target densities: liquid hydrogen, gaseous
hydrogen at NTP and at a low pressure of 5 mbar. The yield of this reaction in
the liquid hydrogen target is smaller than in the low-pressure gas target. The
branching ratios of the channel were calculated on the basis of
simultaneous analysis of the three data samples. The branching ratio for
annihilation into from the protonium state turns out to be
about ten times smaller as compared to the one from the state.Comment: 10 pages, 3 Postscript figures. Accepted by Physics Letters
New data on OZI rule violation in bar{p}p annihilation at rest
The results of a measurement of the ratio R = Y(phi pi+ pi-) / Y(omega pi+
pi-) for antiproton annihilation at rest in a gaseous and in a liquid hydrogen
target are presented. It was found that the value of this ratio increases with
the decreasing of the dipion mass, which demonstrates the difference in the phi
and omega production mechanisms. An indication on the momentum transfer
dependence of the apparent OZI rule violation for phi production from the 3S1
initial state was found.Comment: 11 pages, 3 PostScript figures, submitted to Physics Letter
Polarization Effects in Exclusive Hyperon Production Reactions
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
DISTO: a large acceptance multiparticle spectrometer for 1–3 GeV proton beams
Abstract A magnetic spectrometer system has been constructed for the study of reactions with multiple charged particles in the final state, induced by polarized proton beams of few GeV energy. The system is based on a large-gap dipole magnet, with a liquid hydrogen target and scintillating fiber tracking detectors embedded inside the magnet. Multiwire proportional chambers, plastic scintillator hodoscopes, and threshold Cherenkov detectors placed outside the magnet provide additional tracking, triggering and particle identification capabilities. The system has been applied to study exclusive hyperon as well as pseudoscalar and vector meson production reactions at bombarding energies below 3 GeV. Additionally, it has been used to monitor the proton beam polarization at Laboratoire National Saturne. The components and performance of the system are reported
Antiproton stopping power in He in the energy range 1–900 keV and the Barkas effect
AbstractThe p¯ stopping power in helium from 1 keV kinetic energy is evaluated. Contrary to the effect observed around and below the maximum, Obelix data indicate a p¯ stopping power higher than that for proton, the difference being of the order of 15±5% at ≈700 keV. The result contributes to assert the fundamental difference between p¯ stoppings in the simplest gases (He, H2) and in solid targets below some MeV
Spin asymmetry A_1^d and the spin-dependent structure function g_1^d of the deuteron at low values of x and Q^2
We present a precise measurement of the deuteron longitudinal spin asymmetry
A_1^d and of the deuteron spin-dependent structure function g_1^d at Q^2 < 1
GeV^2 and 4*10^-5 < x < 2.5*10^-2 based on the data collected by the COMPASS
experiment at CERN during the years 2002 and 2003. The statistical precision is
tenfold better than that of the previous measurement in this region. The
measured A_1^d and g_1^d are found to be consistent with zero in the whole
range of x.Comment: 17 pages, 10 figure
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