Fluctuations in statistical models

Proceedings of 4th International Workshop "Critical Point and Onset of Deconfinement", July 9-13, 2007, Darmstadt, Germany: The multiplicity fluctuations of hadrons are studied within the statistical hadron-resonance gas model in the large volume limit. The role of quantum statistics and resonance decay effects are discussed. The microscopic correlator method is used to enforce conservation of three charges - baryon number, electric charge, and strangeness - in the canonical ensemble. In addition, in the micro-canonical ensemble energy conservation is included. An analytical method is used to account for resonance decays. The multiplicity distributions and the scaled variances for negatively and positively charged hadrons are calculated for the sets of thermodynamical parameters along the chemical freeze-out line of central Pb+Pb (Au+Au) collisions from SIS to LHC energies. Predictions obtained within different statistical ensembles are compared with the preliminary NA49 experimental results on central Pb+Pb collisions in the SPS energy range. The measured fluctuations are significantly narrower than the Poisson ones and clearly favor expectations for the micro-canonical ensemble. Thus, this is a first observation of the recently predicted suppression of the multiplicity fluctuations in relativistic gases in the thermodynamical limit due to conservation laws

Research relative to high energy astrophysics

Various parameters which affect the design of the proposed large area modular array of reflectors (LAMAR) are considered, including thermal control, high resolution X-ray spectroscopy, pointing control, and mirror performance. The LAMAR instrument is to be a shuttle-launched X-ray observatory to carry out cosmic X-ray investigations. The capabilities of LAMAR are enumerated. Angular resolution performance of the mirror module prototype was measured to be 30 sec of ARC for 50% of the power. The LAMAR thermal pre-collimator design concepts and test configurations are discussed in detail

Thermodynamical Consistency of Excluded Volume Hadron Gas Models

The new excluded volume hadron gas model by Singh et al. [1-7] is critically discussed. We demonstrate that in this model the results obtained from relations between thermodynamical quantities disagree with the corresponding results obtained by statistical ensemble averaging. Thus, the model does not satisfy the requirements of thermodynamical consistency

Development of high throughput X-ray telescopes for X-ray imaging and dispersive spectrometers

During the past year the technical approach to the realization of a high throughput Kirkpatrick-Baez X-ray mirror became better defined in terms of construction methodology and factors which affect maximum size. More progress was made than anticipated in the area of automatic figure formation. However, effort to improve the resolution of float glass by simple techniques were not successful. Mirror development, spectroscopy, all sky telescope, and explorer concept studies are discussed

Statistical hadronization of charmed quarks at SPS and RHIC

Production of open and hidden charm hadrons in heavy ion collisions is considered within the statistical coalescence model. The charmed quark-antiquark pairs are assumed to be created at the initial stage of the reaction in hard parton collisions. The number of these pairs is conserved during the evolution of the system. At the hadronization stage, the charmed (anti)quarks are distributed among open and hidden charm hadrons in accordance with the laws of statistical mechanics. The model is in agreement with the experimental data on J/psi to Drell-Yan ratio in Pb+Pb collisions at SPS. This agreement can be reached only if a rather strong enhancement of the open charm production in central Pb+Pb collisions is assumed. A possible mechanism of the charm enhancement is discussed. At the top RHIC energy, the model predicts an increase of J/psi to Drell-Yan ratio in more central nucleus-nucleus collisions with respect to less central ones.Comment: Presented at 16th International Conference "Quark Matter", Nantes (France), July 18-24, 2002; 4 pages, LaTeX, 2 PS-figure

On the early stage of nucleus-nucleus collisions

A statistical model of the early stage of central nucleus--nucleus (A+A) collisions is developed. We suggest a description of the confined state with several free parameters fitted to a compilation of A+A data at the AGS. For the deconfined state a simple Bag model equation of state is assumed. The model leads to the conclusion that a Quark Gluon Plasma is created in central nucleus--nucleus collisions at the SPS. This result is in quantitative agreement with existing SPS data on pion and strangeness production and gives a natural explanation for their scaling behaviour. The localization and the properties of the transition region are discussed. It is shown that the deconfinement transition can be detected by observation of the characteristic energy dependence of pion and strangeness multiplicities, and by an increase of the event--by--event fluctuations. An attempt to understand the data on J/psi production in Pb+Pb collisions at the SPS within the same approach is presented

Cumulative production of pions by heavy baryonic resonances in proton-nucleus collisions

Pion production in proton-nucleus (p+A) collisions outside the kinematical boundary of proton-nucleon (p+N) reactions, the so-called cumulative effect, is studied. Restrictions from energy-momentum conservation on the energy of pions emitted in the backward direction in the target rest frame are analyzed. It is assumed that the cumulative pions are produced in p+A reactions by heavy baryonic resonances. The baryonic resonances are first created in p+N reactions. Due to successive collisions with nuclear nucleons the masses of these resonances may then increase and, simultaneously, their longitudinal velocities decrease. We also use the Ultra relativistic Quantum Molecular Dynamics model to reveal the key role of successive collisions of baryonic resonances with nuclear nucleons for cumulative pion production in p+A reactions. Further experimental studies of cumulative hadron production in p+A reactions at high collision energies are needed to search for heavy hadron-like objects and investigate their properties.Comment: 21 pages, 36 figure

Charm estimate from the dilepton spectra in nuclear collisions

A validity of a recent estimate of an upper limit of charm production in central Pb+Pb collisions at 158 AGeV is critically discussed. Within a simple model we study properties of the background subtraction procedure used for an extraction of the charm signal from the analysis of dilepton spectra. We demonstrate that a production asymmetry between positively and negatively charged background muons and a large multiplicity of signal pairs leads to biased results. Therefore the applicability of this procedure for the analysis of nucleus-nucleus data should be reconsidered before final conclusions on the upper limit estimate of charm production could be drawn

Evidence for statistical production of J/psi mesons in nuclear collisions at the CERN SPS

The hypothesis of statistical production of J/psi mesons at hadronization is formulated and checked against experimental data. It explains in the natural way the observed scaling behavior of the J/psi to pion ratio at the CERN SPS energies. Using the multiplicities of J/psi and eta mesons the hadronization temperature T_H = 175 MeV is found, which agrees with the previous estimates of the temperature parameter based on the analysis of the hadron yield systematics