1,193 research outputs found
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
Energy and system size dependence of chemical freeze-out in relativistic nuclear collisions
We present a detailed study of chemical freeze-out in p-p, C-C, Si-Si and
Pb-Pb collisions at beam momenta of 158A GeV as well as Pb-Pb collisions at
beam momenta of 20A, 30A, 40A and 80A GeV. By analyzing hadronic multiplicities
within the statistical hadronization model, we have studied the parameters of
the source as a function of the number of the participating nucleons and the
beam energy. We observe a nice smooth behaviour of temperature, baryon chemical
potential and strangeness under-saturation parameter as a function of energy
and nucleus size. Interpolating formulas are provided which allow to predict
the chemical freeze-out parameters in central collisions at centre-of-mass
energies > 4.5 GeV and for any colliding ions. Specific discrepancies between
data and model emerge in particle ratios in Pb-Pb collisions at SPS between 20A
and 40A GeV of beam energy which cannot be accounted for in the considered
model schemes.Comment: 22 pages, 10 figures. References added and updated. Table correcte
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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