1,492 research outputs found
Dielectron Production in C+C Collisions at 1 GeV/u and the Solution to the DLS Puzzle
The production of e+e- pairs in C+C collisions at 1 GeV/u was investigated
with the HADES experiment at GSI, Darmstadt. In the invariant-mass region the measured pair yield
shows a strong excess above the contribution expected from hadron decays after
freeze-out. The data are in good agreement with the results of the former DLS
experiment for the same system and energy.Comment: 6 pages, 3 figures, conference proceedings: Quark Matter 2008, Jaipur
(India), 4-10 February 2008, submitted to J. Phys. G: Nuclear and Particle
Physic
The HADES Tracking System
The tracking system of the dielectron spectrometer HADES at GSI Darmstadt is
formed out of 24 low-mass, trapezoidal multi-layer drift chambers providing in
total about 30 square meter of active area. Low multiple scattering in the in
total four planes of drift chambers before and after the magnetic field is
ensured by using helium-based gas mixtures and aluminum cathode and field
wires. First in-beam performance results are contrasted with expectations from
simulations. Emphasis is placed on the energy loss information, exploring its
relevance regarding track recognition.Comment: 6 pages, 4 figures, presented at the 10th Vienna Conference on
Instrumentation, Vienna, February 2004, to be published in NIM A (special
issue
Inclusive pion and eta production in p+Nb collisions at 3.5 GeV beam energy
Data on inclusive pion and eta production measured with the dielectron
spectrometer HADES in the reaction p+93Nb at a kinetic beam energy of 3.5 GeV
are presented. Our results, obtained with the photon conversion method,
supplement the rather sparse information on neutral meson production in
proton-nucleus reactions existing for this bombarding energy regime. The
reconstructed e+e-e+e- transverse-momentum and rapidity distributions are
confronted with transport model calculations, which account fairly well for
both pi0 and eta production.Comment: 12 pages, 9 figures, submitted to Physical Review
A versatile method for simulating pp -> ppe+e- and dp -> pne+e-p_spec reactions
We have developed a versatile software package for the simulation of
di-electron production in and collisions at SIS energies. Particular
attention has been paid to incorporate different descriptions of the Dalitz
decay via a common interface. In addition, suitable
parameterizations for the virtual bremsstrahlung process
based on one-boson exchange models have been implemented. Such simulation tools
with high flexibility of the framework are important for the interpretation of
the di-electron data taken with the HADES spectrometer and the design of
forthcoming experiments
Searching a Dark Photon with HADES
We present a search for the e+e- decay of a hypothetical dark photon, also
names U vector boson, in inclusive dielectron spectra measured by HADES in the
p (3.5 GeV) + p, Nb reactions, as well as the Ar (1.756 GeV/u) + KCl reaction.
An upper limit on the kinetic mixing parameter squared epsilon^{2} at 90% CL
has been obtained for the mass range M(U) = 0.02 - 0.55 GeV/c2 and is compared
with the present world data set. For masses 0.03 - 0.1 GeV/c^2, the limit has
been lowered with respect to previous results, allowing now to exclude a large
part of the parameter region favoured by the muon g-2 anomaly. Furthermore, an
improved upper limit on the branching ratio of 2.3 * 10^{-6} has been set on
the helicity-suppressed direct decay of the eta meson, eta-> e+e-, at 90% CL
Lambda hyperon production and polarization in collisions of p(3.5 GeV) + Nb
Results on hyperon production are reported for collisions of p(3.5
GeV) + Nb, studied with the High Acceptance Di-Electron Spectrometer (HADES) at
SIS18 at GSI Helmholtzzentrum for Heavy-Ion Research, Darmstadt. The transverse
mass distributions in rapidity bins are well described by Boltzmann shapes with
a maximum inverse slope parameter of about MeV at a rapidity of ,
i.e. slightly below the center-of-mass rapidity for nucleon-nucleon collisions,
. The rapidity density decreases monotonically with increasing
rapidity within a rapidity window ranging from 0.3 to 1.3. The
phase-space distribution is compared with results of other experiments and with
predictions of two transport approaches which are available publicly. None of
the present versions of the employed models is able to fully reproduce the
experimental distributions, i.e. in absolute yield and in shape. Presumably,
this finding results from an insufficient modelling in the transport models of
the elementary processes being relevant for production, rescattering
and absorption. The present high-statistics data allow for a genuine
two-dimensional investigation as a function of phase space of the
self-analyzing polarization in the weak decay . Finite negative values of the polarization in the order of
are observed over the entire phase space studied. The absolute value of the
polarization increases almost linearly with increasing transverse momentum for
MeV/c and increases with decreasing rapidity for .Comment: accepted by Eur. Phys. J.
Subthreshold Xi- Production in Collisions of p(3.5 GeV)+Nb
Results on the production of the double-strange cascade hyperon
are reported for collisions of p\,(3.5~GeV)\,+\,Nb, studied
with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18 at GSI
Helmholtzzentrum for Heavy-Ion Research, Darmstadt. For the first time,
subthreshold production is observed in proton-nucleus
interactions. Assuming a phase-space distribution similar to
that of hyperons, the production probability amounts to
resulting in a
ratio of $P_{\mathrm{\Xi^-}}/\
P_{\mathrm{\Lambda+\Sigma^0}}=(1.2\pm
0.3\,\mathrm{(stat)}\pm0.4\,\mathrm{(syst)})\times10^{-2}\mathrm{\Xi^-}$ yield.Comment: 6 pages, 3 figure
Medium effects in proton-induced production at 3.5 GeV
We present the analysis of the inclusive production in p+p and p+Nb
collisions measured with the HADES detector at a beam kinetic energy of 3.5
GeV. Data are compared to the GiBUU transport model. The data suggest the
presence of a repulsive momentum-dependent kaon potential as predicted by the
Chiral Perturbation Theory (ChPT). For the kaon at rest and at normal nuclear
density, the ChPT potential amounts to MeV. A detailed tuning of
the kaon production cross sections implemented in the model has been carried
out to reproduce the experimental data measured in p+p collisions. The
uncertainties in the parameters of the model were examined with respect to the
sensitivity of the experimental results from p+Nb collisions to the in-medium
kaon potential.Comment: 13 pages, 14 figure
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