80 research outputs found
Exotic dense-matter states pumped by a relativistic laser plasma in the radiation-dominated regime
In high-spectral resolution experiments with the petawatt Vulcan laser, strong x-ray radiation of KK hollow atoms (atoms without n = 1 electrons) from thin Al foils was observed at pulse intensities of 3 x 10(20) W/cm(2). The observations of spectra from these exotic states of matter are supported by detailed kinetics calculations, and are consistent with a picture in which an intense polychromatic x-ray field, formed from Thomson scattering and bremsstrahlung in the electrostatic fields at the target surface, drives the KK hollow atom production. We estimate that this x-ray field has an intensity of >5 x 10(18) W/cm(2) and is in the 3 keV range
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
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
Inclusive Dielectron Production in Ar+KCl Collisions at 1.76 AGeV studied with HADES
Results of the HADES measurement of inclusive dielectron production in Ar+KCl
collisions at a kinetic beam energy of 1.76 AGeV are presented. For the first
time, high mass resolution spectroscopy was performed. The invariant mass
spectrum of dielectrons is compared with predictions of UrQMD and HSD transport
codes.Comment: 4 pages, 3 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse
Future perspectives at SIS-100 with HADES-at-FAIR
Currently, the HADES spectrometer undergoes un upgrade program to be prepared
for measurements at the upcoming SIS-100 synchrotron at FAIR. We describe the
current status of the HADES di-electron measurements at the SIS-18 and our
future plans for SIS-100.Comment: Invited contribution presented at the XLVII International Winter
Meeting on Nuclear Physics, Bormio (Italy), Jan. 26-30, 200
Measurement of the Spin-Dependence of the pbar-p Interaction at the AD-Ring
We propose to use an internal polarized hydrogen storage cell gas target in
the AD ring to determine for the first time the two total spin-dependent pbar-p
cross sections sigma_1 and sigma_2 at antiproton beam energies in the range
from 50 to 450 MeV. The data obtained are of interest by themselves for the
general theory of pbar-p interactions since they will provide a first
experimental constraint of the spin-spin dependence of the nucleon-antinucleon
potential in the energy range of interest. In addition, measurements of the
polarization buildup of stored antiprotons are required to define the optimum
parameters of a future, dedicated Antiproton Polarizer Ring (APR), intended to
feed a double-polarized asymmetric pbar-p collider with polarized antiprotons.
Such a machine has recently been proposed by the PAX collaboration for the new
Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt, Germany.
The availability of an intense stored beam of polarized antiprotons will
provide access to a wealth of single- and double-spin observables, thereby
opening a new window on QCD spin physics.Comment: 51 pages, 23 figures, proposal submitted to the SPS committee of CER
Binding of Superantigen Toxins into the CD28 Homodimer Interface Is Essential for Induction of Cytokine Genes That Mediate Lethal Shock
Bacterial superantigen toxins bind directly to the dimer interface of CD28, the principal co-stimulatory receptor, to induce a lethal cytokine storm, and peptides that prevent this binding can suppress superantigen lethality
Measurement of charged pions in 12C + 12C collisions at 1A GeV and 2A GeV with HADES
We present the results of a study of charged pion production in 12C + 12C
collisions at incident beam energies of 1A GeV and 2A GeV using the HADES
spectrometer at GSI. The main emphasis of the HADES program is on the
dielectron signal from the early phase of the collision. Here, however, we
discuss the data with respect to the emission of charged hadrons, specifically
the production of pi+- mesons, which are related to neutral pions representing
a dominant contribution to the dielectron yield. We have performed the first
large-angular range measurement of the distribution of pi+- mesons for the 12C
+ 12C collision system covering a fairly large rapidity interval. The pion
yields, transverse-mass and angular distributions are compared with
calculations done within a transport model, as well as with existing data from
other experiments. The anisotropy of pion production is systematically
analyzed.Comment: 15 pages, 13 figures, v2 - the text unchanged, only full author list
added to METADATA (in v1 only the first author and collaboration name),
reference to published paper adde
Charged pion production in C+C and Ar+KCl collisions measured with HADES
Results of a study of charged pion production in 12C+12C collisions at
incident beam energies of 1A GeV and 2A GeV, and 40Ar+natKCl at 1.76AGeV, using
the spectrometer HADES at GSI, are presented. We have performed a measurement
of the transverse momentum distributions of pi+- mesons covering a fairly large
rapidity interval, in case of the C+C collision system for the first time. The
yields, transverse mass and angular distributions are compared with a transport
model as well as with existing data from other experiments.Comment: 7 pages, 2 figures Contribution presented at the XLVII International
Winter Meeting on Nuclear Physics, Bormio (Italy), Jan. 26-30, 200
Phi decay: a relevant source for K- production at SIS energies?
We present phase space distributions and multiplicities of K+, K- and phi
mesons produced in Ar+KCl reactions at a kinetic beam energy of 1.756 AGeV and
measured with the HADES spectrometer. The inverse slope parameters and yields
of kaons supplement the systematics of previous measurements. The percentage of
K- mesons coming fromphi decay is found to be 18+- 7%
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