177 research outputs found
Baryon stopping in 40 and 158 GeV/nucleon Pb+Pb collisions
Proton rapidity distributions have been measured by the NA49 collaboration in
40 and 158 GeV/nucleon Pb+Pb collisions as function of collision centrality. We
find that the shape and the yield per wounded nucleon in the mid-rapidity
region vary little with centrality and are similar to the distributions
obtained from inelastic p+p interactions. This observation is satisfactorily
described by the transport models HSD and UrQMD, although there are significant
differences in the details of the spectral shape between the experimental data
and the models as well as between the models. The approximate invariance of the
normalized proton spectrum in the vicinity of mid-rapidity suggests that
multiple nucleon-nucleon interactions in nuclear collisions at SPS energies
have little effect on the spectra of those final state protons which are slowed
down the most.Comment: CPOD 2009 Proceedings, NA49 Collaboration, 10 page
The RHIC Zero Degree Calorimeter
High Energy collisions of nuclei usually lead to the emission of evaporation
neutrons from both ``beam'' and ``target'' nuclei. At the RHIC heavy ion
collider with 100GeV/u beam energy, evaporation neutrons diverge by less than
milliradians from the beam axis Neutral beam fragments can be detected
downstream of RHIC ion collisions (and a large aperture Accelerator dipole
magnet) if 4 mr but charged fragments in the same angular range
are usually too close to the beam trajectory.
In this 'zero degree' region produced particles and other secondaries deposit
negligible energy when compared with that of beam fragmentation neutrons.
The purpose of the RHIC zero degree calorimeters (ZDC's) is to detect
neutrons emitted within this cone along both beam directions and measure their
total energy (from which we calculate multiplicity). The ZDC coincidence of the
2 beam directions is a minimal bias selection of heavy ion collisions. This
makes it useful as an event trigger and a luminosity monitor\cite{baltz} and
for this reason we built identical detectors for all 4 RHIC experiments.
The neutron multiplicity is also known to be correlated with event geometry
\cite{appel} and will be used to measure collision centrality in mutual beam
int eractions.Comment: 18 pages, 12 figure
Evidence for a Soft Nuclear Equation-of-State from Kaon Production in Heavy Ion Collisions
The production of pions and kaons has been measured in Au+Au collisions at
beam energies from 0.6 to 1.5 AGeV with the Kaon Spectrometer at SIS/GSI. The
K+ meson multiplicity per nucleon is enhanced in Au+Au collisions by factors up
to 6 relative to C+C reactions whereas the corresponding pion ratio is reduced.
The ratio of the K+ meson excitation functions for Au+Au and C+C collisions
increases with decreasing beam energy. This behavior is expected for a soft
nuclear equation-of-state.Comment: 14 pages, 2 figures, accepted for publication in Phys. Rev. Let
Production of Charged Pions, Kaons and Antikaons in Relativistic C+C and C+Au Collisions
Production cross sections of charged pions, kaons and antikaons have been
measured in C+C and C+Au collisions at beam energies of 1.0 and 1.8 AGeV for
different polar emission angles. The kaon and antikaon energy spectra can be
described by Boltzmann distributions whereas the pion spectra exhibit an
additional enhancement at low energies. The pion multiplicity per participating
nucleon M(pi+)/A_part is a factor of about 3 smaller in C+Au than in C+C
collisions at 1.0 AGeV whereas it differs only little for the C and the Au
target at a beam energy of 1.8 AGeV. The K+ multiplicities per participating
nucleon M(K+)/A_part are independent of the target size at 1 AGeV and at 1.8
AGeV. The K- multiplicity per participating nucleon M(K-)/A_part is reduced by
a factor of about 2 in C+Au as compared to C+C collisions at 1.8 AGeV. This
effect might be caused by the absorption of antikaons in the heavy target
nucleus. Transport model calculations underestimate the K-/K+ ratio for C+C
collisions at 1.8 AGeV by a factor of about 4 if in-medium modifications of K
mesons are neglected.Comment: 19 pages, 14 figures, accepted for publication in Eur. Phys. J.
Enhanced Out-of-plane Emission of K+ Mesons observed in Au+Au Collisions at 1 AGeV
The azimuthal angular distribution of K+ mesons has been measured in Au + Au
collisions at 1 AGeV. In peripheral and semi-central collisions, K+ mesons
preferentially are emitted perpendicular to the reaction plane. The strength of
the azimuthal anisotropy of K+ emission is comparable to the one of pions. No
in-plane flow was found for K+ mesons near projectile and target rapidity.Comment: Accepted for publication in Phys. Rev.Let
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
SINFONI - Integral Field Spectroscopy at 50 milli-arcsecond resolution with the ESO VLT
SINFONI is an adaptive optics assisted near-infrared integral field
spectrometer for the ESO VLT. The Adaptive Optics Module (built by the ESO
Adaptive Optics Group) is a 60-elements curvature-sensor based system, designed
for operations with natural or sodium laser guide stars. The near-infrared
integral field spectrometer SPIFFI (built by the Infrared Group of MPE)
provides simultaneous spectroscopy of 32 x 32 spatial pixels, and a spectral
resolving power of up to 3300. The adaptive optics module is in the phase of
integration; the spectrometer is presently tested in the laboratory. We provide
an overview of the project, with particular emphasis on the problems
encountered in designing and building an adaptive optics assisted spectrometer.Comment: This paper was published in Proc. SPIE, 4841, pp. 1548-1561 (2003),
and is made available as an electronic reprint with permission of SPIE.
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