1,655 research outputs found
Dilepton production in proton-proton collisions at top RHIC energy
We study dielectron production in proton-proton collisions at top RHIC beam
energy within an extended statistical hadronization model. The invariant mass
spectrum of correlated dielectron pairs is evaluated in the low invariant mass
region and calculated results are compared with the PHENIX experiment. The
model is found to be able to describe the data very well up to invariant masses
of 1 GeV with few adjustable parameters.Comment: Proceedings of Hot Quarks 201
Dilepton production in p+p, Cu+Cu and Au+Au collisions at 200 AGeV
We study dilepton production in proton-proton, Cu+Cu as well as in Au+Au
collisions at the center-of-mass energy 200 GeV per participating nucleon pair
within an extended statistical hadronization model. In extension to earlier
studies we incorporate transport calculations for an estimate of uncorrelated
e+e- -pairs from semileptonic D meson decays. While the invariant mass spectrum
of dielectrons is well understood in the p+p collisions, severe discrepancies
among different model scenarios based on hadronic degrees of freedom and recent
data from the PHENIX Collaboration are found in heavy-ion collisions in the low
mass region from 0.15 to 0.6 GeV as well as in the intermediate mass regime
from 1.1 to 3 GeV when employing the standard dilepton sources. We investigate,
furthermore, the background from correlated dileptons that are not emitted as a
pair from a parent hadron but emerge from semileptonic decays of two correlated
daughter hadrons. Our calculations suggest a sizeable contribution of such
sources in central heavy-ion collisions in the low mass region. However, even
the upper limits of our calculations are found to be far below the dilepton
mass spectra of the PHENIX Collaboration.Comment: revised version, 17 pages, 13 figure
Chemical equilibrium study in nucleus-nucleus collisions at relativistic energies
We present a detailed study of chemical freeze-out in nucleus-nucleus
collisions at beam energies of 11.6, 30, 40, 80 and 158A GeV. By analyzing
hadronic multiplicities within the statistical hadronization approach, we have
studied the strangeness production as a function of centre of mass energy and
of the parameters of the source. We have tested and compared different versions
of the statistical model, with special emphasis on possible explanations of the
observed strangeness hadronic phase space under-saturation. We show that, in
this energy range, the use of hadron yields at midrapidity instead of in full
phase space artificially enhances strangeness production and could lead to
incorrect conclusions as far as the occurrence of full chemical equilibrium is
concerned. In addition to the basic model with an extra strange quark
non-equilibrium parameter, we have tested three more schemes: a two-component
model superimposing hadrons coming out of single nucleon-nucleon interactions
to those emerging from large fireballs at equilibrium, a model with local
strangeness neutrality and a model with strange and light quark non-equilibrium
parameters. The behaviour of the source parameters as a function of colliding
system and collision energy is studied. The description of strangeness
production entails a non-monotonic energy dependence of strangeness saturation
parameter gamma_S with a maximum around 30A GeV. We also present predictions of
the production rates of still unmeasured hadrons including the newly discovered
Theta^+(1540) pentaquark baryon.Comment: 36 pages, 14 figures. Revised version published in Phys. Rev. C:
title changed, one paragraph added in section 2, other typos correcte
Superconducting MoSi nanowires
We have fabricated disordered superconducting nanowires of molybdenium
silicide. A molybdenium nanowire is first deposited on top of silicon, and the
alloy is formed by rapid thermal annealing. The method allows tuning of the
crystal growth to optimise, e.g., the resistivity of the alloy for potential
applications in quantum phase slip devices and superconducting nanowire
single-photon detectors. The wires have effective diameters from 42 to 79 nm,
enabling the observation of crossover from conventional superconductivity to
regimes affected by thermal and quantum fluctuations. In the smallest diameter
wire and at temperatures well below the superconducting critical temperature,
we observe residual resistance and negative magnetoresistance, which can be
considered as fingerprints of quantum phase slips
Chemical equilibrium study at SPS 158A GeV
A detailed study of chemical freeze-out in nucleus-nucleus collisions at beam
energy 158A GeV is presented. By analyzing hadronic multiplicities within the
statistical hadronization approach, the chemical equilibration of p-p, C-C,
Si-Si and Pb-Pb systems is studied as a function of the number of participating
nucleons in the system. Additionally, Two Component statistical hadronization
model is applied to the data and is found to be able to explain the observed
strangeness hadronic phase space under-saturation.Comment: 4 pages, 3 figures to appear in the proceedings of the ''Strangeness
in Quark Matter 2004'' conferenc
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