Chemical Equilibrium in Collisions of Small Systems

The system-size dependence of particle production in heavy-ion collisions at the top SPS energy is analyzed in terms of the statistical model. A systematic comparison is made of two suppression mechanisms that quantify strange particle yields in ultra-relativistic heavy-ion collisions: the canonical model with strangeness correlation radius determined from the data and the model formulated in the canonical ensemble using chemical off-equilibrium strangeness suppression factor. The system-size dependence of the correlation radius and the thermal parameters are obtained for p-p, C-C, Si-Si and Pb-Pb collisions at sqrt(s_NN) = 17.3 AGeV. It is shown that on the basis of a consistent set of data there is no clear difference between the two suppression patterns. In the present study the strangeness correlation radius was found to exhibit a rather weak dependence on the system size.Comment: 9 pages, 8 figures, submitted to Physical Review

Quantum Mechanical Localization Effects for Bose-Einstein Correlations

For a set of N identical massive boson wavepackets with optimal initial quantum mechanical localization, we derive the Hanbury-Brown/Twiss (HBT) two-particle correlation function. Our result provides finite multiplicity corrections to the coherent state formalism and allows to trace back an error in the so-called cos-prescription. It suggests that what the HBT radius parameters in very small boson emitting systems (e.g. Z_0-decays, p-pbar annihilation) measure is essentially the initial spatial wavepacket width. Both one- and two-particle spectra depend explicitly on this width. Our derivation gives an algorithm for calculating one-particle spectra and two-particle correlations from an arbitrary phase space occupation (q_i,p_i,t_i) as e.g. returned by event generators of heavy ion collisions

Status of Chemical Equilibrium in Relativistic Heavy Ion Collisions

Recent work on chemical equilibrium in heavy ion collisions is reviewed. The energy dependence of thermal parameters is discussed. The centrality dependence of thermal parameters at SPS energies is presented.Comment: 7 pages, 7 Postscript figure

Thermal analysis of hadron multiplicities from relativistic quantum molecular dynamics

Some questions arising in the application of the thermal model to hadron production in heavy ion collisions are studied. We do so by applying the thermal model of hadron production to particle yields calculated by the microscopic transport model RQMD(v2.3). We study the bias of incomplete information about the final hadronic state on the extraction of thermal parameters.It is found that the subset of particles measured typically in the experiments looks more thermal than the complete set of stable particles. The hadrons which show the largest deviations from thermal behaviour in RQMD(v2.3) are the multistrange baryons and antibaryons. We also looked at the influence of rapidity cuts on the extraction of thermal parameters and found that they lead to different thermal parameters and larger disagreement between the RQMD yields and the thermal model.Comment: 12 pages, 2 figures, uses REVTEX, only misprint and stylistic corrections, to appear in Physical Review

Gluon Radiation and Coherent States in Ultrarelativistic Nuclear Collisions

We explore the correspondence between classical gluon radiation and quantum radiation in a coherent state for gluons produced in ultrarelativistic nuclear collisions. The expectation value of the invariant momentum distribution of gluons in the coherent state is found to agree with the gluon number distribution obtained classically from the solution of the Yang-Mills equations. A criterion for the applicability of the coherent state formalism to the problem of radiation in ultrarelativistic nucleus-nucleus collisions is discussed. This criterion is found to be fulfilled for midrapidity gluons with perturbative transverse momenta larger than about 1-2 GeV and produced in collisions between valence partons.Comment: 15 pages, 6 figures, RevTeX (with epsf, psfig style files

Using conceptual metaphor and functional grammar to explore how language used in physics affects student learning

This paper introduces a theory about the role of language in learning physics. The theory is developed in the context of physics students' and physicists' talking and writing about the subject of quantum mechanics. We found that physicists' language encodes different varieties of analogical models through the use of grammar and conceptual metaphor. We hypothesize that students categorize concepts into ontological categories based on the grammatical structure of physicists' language. We also hypothesize that students over-extend and misapply conceptual metaphors in physicists' speech and writing. Using our theory, we will show how, in some cases, we can explain student difficulties in quantum mechanics as difficulties with language.Comment: Accepted for publication in Phys. Rev. ST:PE

Strange Messages: Chemical and Thermal Freeze-out in Nuclear Collisions

Thermal models are commonly used to interpret heavy-ion data on particle yields and spectra and to extract the conditions of chemical and thermal freeze-out in heavy-ion collisions. I discuss the usefulness and limitations of such thermal model analyses and review the experimental and theoretical evidence for thermalization in nuclear collisions. The crucial role of correlating strangeness production data with single particle spectra and two-particle correlation measurements is pointed out. A consistent dynamical picture for the heavy-ion data from the CERN SPS involves an initial prehadronic stage with deconfined color and with an appreciable isotropic pressure component. This requires an early onset of thermalization.Comment: 15 pages, 2 figures, talk given at Strange Quark Matter '98, Padova, Italy, 20-24 July 1998, to be published in J. Phys. G 25; final version with updated reference

Quantum radiation in external background fields

A canonical formalism is presented which allows for investigations of quantum radiation induced by localized, smooth disturbances of classical background fields by means of a perturbation theory approach. For massless, non-selfinteracting quantum fields at zero temperature we demonstrate that the low-energy part of the spectrum of created particles exhibits a non-thermal character. Applied to QED in varying dielectrics the response theory approach facilitates to study two distinct processes contributing to the production of photons: the squeezing effect due to space-time varying properties of the medium and of the velocity effect due to its motion. The generalization of this approach to finite temperatures as well as the relation to sonoluminescence is indicated.Comment: 20 page

PRIDE: Quality control in a proteomics data repository

The PRoteomics IDEntifications (PRIDE) database is a large public proteomics data repository, containing over 270 million mass spectra (by November 2011). PRIDE is an archival database, providing the proteomics data supporting specific scientific publications in a computationally accessible manner. While PRIDE faces rapid increases in data deposition size as well as number of depositions, the major challenge is to ensure a high quality of data depositions in the context of highly diverse proteomics work flows and data representations. Here, we describe the PRIDE curation pipeline and its practical application in quality control of complex data depositions