226 research outputs found
Single-Pion Production in pp Collisions at 0.95 GeV/c (II)
The single-pion production reactions , and
were measured at a beam momentum of 0.95 GeV/c (
400 MeV) using the short version of the COSY-TOF spectrometer. The central
calorimeter provided particle identification, energy determination and neutron
detection in addition to time-of-flight and angle measurements from other
detector parts. Thus all pion production channels were recorded with 1-4
overconstraints. Main emphasis is put on the presentation and discussion of the
channel, since the results on the other channels have already been
published previously. The total and differential cross sections obtained are
compared to theoretical calculations. In contrast to the channel we
find in the channel a strong influence of the excitation
already at this energy close to threshold. In particular we find a dependence in the pion angular distribution, typical for a
pure s-channel excitation and identical to that observed in the
channel. Since the latter is understood by a s-channel resonance in
the partial wave, we discuss an analogous scenario for the
channel
Comparison of Isoscalar Vector Meson Production Cross Sections in Proton-Proton Collisions
The reaction was investigated with the TOF
spectrometer, which is an external experiment at the accelerator COSY
(Forschungszentrum J\"ulich, Germany). Total as well as differential cross
sections were determined at an excess energy of (). Using the total cross section of for the
reaction determined here and existing data for the reaction
, the ratio
turns out to be
significantly larger than expected by the Okubo-Zweig-Iizuka (OZI) rule. The
uncertainty of this ratio is considerably smaller than in previous
determinations. The differential distributions show that the
production is still dominated by S-wave production at this excess energy,
however higher partial waves clearly contribute. A comparison of the measured
angular distributions for production to published distributions for
production at shows that the data are consistent with an
identical production mechanism for both vector mesons
Production of mesons in proton-proton collisions
The cross section for the production of mesons in proton-proton
collisions has been measured in a previously unexplored region of incident
energies. Cross sections were extracted at 92 MeV and 173 MeV excess energy,
respectively. The angular distribution of the at =173 MeV is
strongly anisotropic, demonstrating the importance of partial waves beyond pure
s-wave production at this energy.Comment: 12 pages, 4 figures submitted to Physics Letters B v2: figure 1
added, discussion detailing the data analysis, figure 3 (fig. 2 in v1)
modified in line styles and systematic errors displayed on dat
On the Production of Pairs in pp Collisions at 0.8 GeV
Data accumulated recently for the exclusive measurement of the reaction at a beam energy of 0.793 GeV using the COSY-TOF
spectrometer have been analyzed with respect to possible events from the reaction channel. The latter is expected to be the only
production channel, which contains no major contributions from
resonance excitation close to threshold and hence should be a good testing
ground for chiral dynamics in the production process. No single event
has been found, which meets all conditions for being a candidate for the reaction. This gives an upper limit for the cross section of
0.16 b (90% C.L.), which is more than an order of magnitude smaller than
the cross sections of the other two-pion production channels at the same
incident energy
Systematic study of the pp -> pp omega reaction
A systematic study of the production of omega-mesons in
proton-proton-collisions was carried out in a kinematically complete experiment
at three excess energies(epsilon= 92, 128, 173MeV). Both protons were detected
using the large-acceptance COSY-TOF spectrometer at an external beam line at
the Cooler Synchrotron COSY at Forschungszentrum J\"ulich. The total cross
section, angular distributions of both omega-mesons and protons were measured
and presented in various reference frames such as the overall CMS, helicity and
Jackson frame. In addition, the orientation of the omega-spin and invariant
mass spectra were determined. We observe omega-production to take place
dominantly in Ss and Sp final states at epsilon = 92, 128 MeV and,
additionally, in Sd at epsilon= 173 MeV. No obvious indication of resonant
omega-production via N^*-resonances was found, as proton angular distributions
are almost isotropic and invariant mass spectra are compatible with phase space
distributions. A dominant role of ^3P_1 and ^1S_0 initial partial waves for
omega-production was concluded from the orientation of the decay plane of the
omega-meson. Although the Jackson angle distributions in the omega-p-Jackson
frame are anisotropic we argue that this is not an indication of a resonance
but rather a kinematical effect reflecting the anisotropy of the omega angular
distribution. The helicity angle distribution in the omega-p-helicity frame
shows an anisotropy which probably reflects effects of the omega angular
momenta in the final state; this observable may be, in addition to the
orientation of the omega decay plane, the most sensitive one to judge the
validity of theoretical descriptions of the production process.Comment: 17 pages, 16 figures, accepted for publication in EPJ
Production of Lambda and Sigma^0 hyperons in proton-proton collisions
This paper reports results on simultaneous measurements of the reaction
channels pp -> pK+\Lambda and pp -> pK+\Sigma^0 at excess energies of 204, 239,
and 284 MeV (\Lambda) and 127, 162, and 207 MeV (\Sigma^0). Total and
differential cross sections are given for both reactions. It is concluded from
the measured total cross sections that the high energy limit of the cross
section ratio is almost reached at an excess energy of only about 200 MeV. From
the differential distributions observed in the overall CMS as well as in the
Jackson and helicity frames, a significant contribution of interfering nucleon
resonances to the \Lambda production mechanism is concluded while resonant
\Sigma^0-production seems to be of lesser importance and takes place only
through specific partial waves of the entrance channel. The data also indicate
that kaon exchange plays a minor role in the case of \Lambda- but an important
role for \Sigma^0-production. Thus the peculiar energy dependence of the
\Lambda-to-\Sigma^0 cross section ratio appears in a new light as its
explanation requires more than mere differences between the p\Lambda and the
p\Sigma^0 final state interaction. The data provide a benchmark for theoretical
models already available or yet to come.Comment: 18 pages, 10 figures; accepted by The European Physical Journal A
(EPJ A
Acoustic and optical variations during rapid downward motion episodes in the deep north-western Mediterranean Sea
An Acoustic Doppler Current Profiler (ADCP) was moored at the deep-sea site
of the ANTARES neutrino telescope near Toulon, France, thus providing a unique
opportunity to compare high-resolution acoustic and optical observations
between 70 and 170 m above the sea bed at 2475 m. The ADCP measured downward
vertical currents of magnitudes up to 0.03 m s-1 in late winter and early
spring 2006. In the same period, observations were made of enhanced levels of
acoustic reflection, interpreted as suspended particles including zooplankton,
by a factor of about 10 and of horizontal currents reaching 0.35 m s-1. These
observations coincided with high light levels detected by the telescope,
interpreted as increased bioluminescence. During winter 2006 deep dense-water
formation occurred in the Ligurian subbasin, thus providing a possible
explanation for these observations. However, the 10-20 days quasi-periodic
episodes of high levels of acoustic reflection, light and large vertical
currents continuing into the summer are not direct evidence of this process. It
is hypothesized that the main process allowing for suspended material to be
moved vertically later in the year is local advection, linked with topographic
boundary current instabilities along the rim of the 'Northern Current'.Comment: 30 pages, 7 figure
Status and Recent Results of the Acoustic Neutrino Detection Test System AMADEUS
The AMADEUS system is an integral part of the ANTARES neutrino telescope in
the Mediterranean Sea. The project aims at the investigation of techniques for
acoustic neutrino detection in the deep sea. Installed at a depth of more than
2000m, the acoustic sensors of AMADEUS are based on piezo-ceramics elements for
the broad-band recording of signals with frequencies ranging up to 125kHz.
AMADEUS was completed in May 2008 and comprises six "acoustic clusters", each
one holding six acoustic sensors that are arranged at distances of roughly 1m
from each other. The clusters are installed with inter-spacings ranging from
15m to 340m. Acoustic data are continuously acquired and processed at a
computer cluster where online filter algorithms are applied to select a
high-purity sample of neutrino-like signals. 1.6 TB of data were recorded in
2008 and 3.2 TB in 2009. In order to assess the background of neutrino-like
signals in the deep sea, the characteristics of ambient noise and transient
signals have been investigated. In this article, the AMADEUS system will be
described and recent results will be presented.Comment: 7 pages, 8 figures. Proceedings of ARENA 2010, the 4th International
Workshop on Acoustic and Radio EeV Neutrino Detection Activitie
The ANTARES Telescope Neutrino Alert System
The ANTARES telescope has the capability to detect neutrinos produced in
astrophysical transient sources. Potential sources include gamma-ray bursts,
core collapse supernovae, and flaring active galactic nuclei. To enhance the
sensitivity of ANTARES to such sources, a new detection method based on
coincident observations of neutrinos and optical signals has been developed. A
fast online muon track reconstruction is used to trigger a network of small
automatic optical telescopes. Such alerts are generated for special events,
such as two or more neutrinos, coincident in time and direction, or single
neutrinos of very high energy.Comment: 17 pages, 9 figures submitted to Astroparticle Physic
Measurement of Atmospheric Neutrino Oscillations with the ANTARES Neutrino Telescope
The data taken with the ANTARES neutrino telescope from 2007 to 2010, a total
live time of 863 days, are used to measure the oscillation parameters of
atmospheric neutrinos. Muon tracks are reconstructed with energies as low as 20
GeV. Neutrino oscillations will cause a suppression of vertical upgoing muon
neutrinos of such energies crossing the Earth. The parameters determining the
oscillation of atmospheric neutrinos are extracted by fitting the event rate as
a function of the ratio of the estimated neutrino energy and reconstructed
flight path through the Earth. Measurement contours of the oscillation
parameters in a two-flavour approximation are derived. Assuming maximum mixing,
a mass difference of eV is
obtained, in good agreement with the world average value.Comment: 9 pages, 5 figure
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