6,126 research outputs found
Electron impact excitation cross sections for allowed transitions in atoms
We present a semiempirical Gaunt factor for widely used Van Regemorter
formula [Astrophys. J. 136, 906 (1962)] for the case of allowed transitions in
atoms with the LS coupling scheme. Cross sections calculated using this Gaunt
factor agree with measured cross sections to within the experimental error.Comment: RevTeX, 3 pages, 10 PS figures, 2 PS tables, submitted to Phys. Rev.
An upper limit on hypertriton production in collisions of Ar(1.76 AGeV)+KCl
A high-statistic data sample of Ar(1.76 AGeV)+KCl events recorded with HADES
is used to search for a hypertriton signal. An upper production limit per
centrality-triggered event of x on the level is
derived. Comparing this value with the number of successfully reconstructed
hyperons allows to determine an upper limit on the ratio
, which is confronted with statistical and
coalescence-type model calculations
Inclusive dielectron production in proton-proton collisions at 2.2 GeV beam energy
Data on inclusive dielectron production are presented for the reaction p+p at
2.2 GeV measured with the High Acceptance DiElectron Spectrometer (HADES). Our
results supplement data obtained earlier in this bombarding energy regime by
DLS and HADES. The comparison with the 2.09 GeV DLS data is discussed. The
reconstructed e+e- distributions are confronted with simulated pair cocktails,
revealing an excess yield at invariant masses around 0.5 GeV/c2. Inclusive
cross sections of neutral pion and eta production are obtained
Deep sub-threshold production in Ar+KCl reactions at 1.76A GeV
We report first results on a deep sub-threshold production of the doubly
strange hyperon in a heavy-ion reaction. At a beam energy of 1.76A GeV
the reaction Ar+KCl was studied with the High Acceptance Di-Electron
Spectrometer (HADES) at SIS18/GSI. A high-statistics and high-purity
sample was collected, allowing for the investigation of the decay channel
. The deduced production
ratio of is significantly larger
than available model predictions.Comment: 4 pages, including 4 figure
Study of the quasi-free reaction with a deuterium beam at 1.25 GeV/nucleon
The tagged quasi-free reaction has been studied
experimentally with the High Acceptance Di-Electron Spectrometer (HADES) at GSI
at a deuteron incident beam energy of 1.25 GeV/nucleon ( 2.42
GeV/c for the quasi-free collision). For the first time, differential
distributions for production in collisions have been
collected in the region corresponding to the large transverse momenta of the
secondary particles. The invariant mass and angular distributions for the
reaction are compared with different models.
This comparison confirms the dominance of the -channel with
contribution. It also validates the changes previously introduced in the
Valencia model to describe two-pion production data in other isospin channels,
although some deviations are observed, especially for the
invariant mass spectrum. The extracted total cross section is also in much
better agreement with this model. Our new measurement puts useful constraints
for the existence of the conjectured dibaryon resonance at mass M 2.38
GeV and with width 70 MeV
The High-Acceptance Dielectron Spectrometer HADES
HADES is a versatile magnetic spectrometer aimed at studying dielectron
production in pion, proton and heavy-ion induced collisions. Its main features
include a ring imaging gas Cherenkov detector for electron-hadron
discrimination, a tracking system consisting of a set of 6 superconducting
coils producing a toroidal field and drift chambers and a multiplicity and
electron trigger array for additional electron-hadron discrimination and event
characterization. A two-stage trigger system enhances events containing
electrons. The physics program is focused on the investigation of hadron
properties in nuclei and in the hot and dense hadronic matter. The detector
system is characterized by an 85% azimuthal coverage over a polar angle
interval from 18 to 85 degree, a single electron efficiency of 50% and a vector
meson mass resolution of 2.5%. Identification of pions, kaons and protons is
achieved combining time-of-flight and energy loss measurements over a large
momentum range. This paper describes the main features and the performance of
the detector system
In-Medium Effects on K0 Mesons in Relativistic Heavy-Ion Collisions
We present the transverse momentum spectra and rapidity distributions of
and K in Ar+KCl reactions at a beam kinetic energy of 1.756 A
GeV measured with the spectrometer HADES. The reconstructed K sample is
characterized by good event statistics for a wide range in momentum and
rapidity. We compare the experimental and K distributions to
predictions by the IQMD model. The model calculations show that K at low
tranverse momenta constitute a particularly well suited tool to investigate the
kaon in-medium potential. Our K data suggest a strong repulsive in-medium
K potential of about 40 MeV strength.Comment: 10 pages, 10 figures, accepted by Phys. Rev.
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