György Wolf

Existence of the critical endpoint in the vector meson extended linear sigma model

The chiral phase transition of the strongly interacting matter is investigated at nonzero temperature and baryon chemical potential (μB) within an extended (2+1) flavor Polyakov constituent quark-meson model that incorporates the effect of the vector and axial vector mesons. The effect of the fermionic vacuum and thermal fluctuations computed from the grand potential of the model is taken into account in the curvature masses of the scalar and pseudoscalar mesons. The parameters of the model are determined by comparing masses and tree-level decay widths with experimental values in a χ2-minimization procedure that selects between various possible assignments of scalar nonet states to physical particles. We examine the restoration of the chiral symmetry by monitoring the temperature evolution of condensates and the chiral partners’ masses and of the mixing angles for the pseudoscalar η-η′ and the corresponding scalar complex. We calculate the pressure and various thermodynamical observables derived from it and compare them to the continuum extrapolated lattice results of the Wuppertal-Budapest collaboration. We study the T-μB phase diagram of the model and find that a critical endpoint exists for parameters of the model, which give acceptable values of χ2.

A LINEAR SIGMA MODEL WITH THREE FLAVORS AND VECTOR AND AXIAL-VECTOR MESONS

We outline the extension of the globally chirally invariant Nf = 2 linear sigma model with vector and axial-vector degrees of freedom to Nf = 3. We present preliminary results concerning the scalar meson masses.

Dilepton production in pion-nucleon collisions in an effective field theory approach

We present a model of electron-positron pair production in pion-nucleon collisions in the exclusive reaction \pi N -> Ne^+e^-. The model is based on an effective field theory approach, incorporating 16 baryon resonances below 2 GeV. Parameters of the model are fitted to pion photoproduction data. We present the resulting dilepton invariant mass spectra for \pi^- p collisions up to sqrt(s)=1.9 GeV center-of-mass collision energy. These results are meant to give predictions for the planned experiments at the HADES spectrometer in GSI, Darmstadt.

Zero temperature properties of mesons in a vector meson extended linear sigma model

A three flavor linear sigma model with vector and axial-vector mesons is discussed. Preliminary results concerning on the symmetry breaking pattern, the question of parameterization, as well as the resulting meson masses are presented.

Mass shift of charmonium states in p¯A collision

Abstract The masses of the low lying charmonium states, namely, the J / Ψ , Ψ ( 3686 ) , and Ψ ( 3770 ) are shifted downwards due to the second order Stark effect. In p ¯ + Au collisions at 6–10 GeV we study their in-medium propagation. The time evolution of the spectral functions of these charmonium states is studied with a Boltzmann–Uehling–Uhlenbeck (BUU) type transport model. We show that their in-medium mass shift can be observed in the dilepton spectrum. Therefore, by observing the dileptonic decay channel of these low lying charmonium states, especially for Ψ ( 3686 ) , we can gain information about the magnitude of the gluon condensate in nuclear matter. This measurement could be performed at the upcoming PANDA experiment at FAIR.

A statistical method to estimate low-energy hadronic cross sections

Abstract.In this article we propose a model based on the Statistical Bootstrap approach to estimate the cross sections of different hadronic reactions up to a few GeV in c.m.s. energy. The method is based on the idea, when two particles collide a so-called fireball is formed, which after a short time period decays statistically into a specific final state. To calculate the probabilities we use a phase space description extended with quark combinatorial factors and the possibility of more than one fireball formation. In a few simple cases the probability of a specific final state can be calculated analytically, where we show that the model is able to reproduce the ratios of the considered cross sections. We also show that the model is able to describe proton-antiproton annihilation at rest. In the latter case we used a numerical method to calculate the more complicated final state probabilities. Additionally, we examined the formation of strange and charmed mesons as well, where we used existing data to fit the relevant model parameters.

Baryonic channels of dilepton production

A calculation of the Dalitz-decay width of baryon resonances is presented and applied to dilepton production in proton-proton collisions in the BEVALAC/SIS energy range. The results indicate, that for these energies the contribution of Dalitz decay of higher baryon resonances (i.e. other that the δ(1232)) are negligible.

Influence of anisotropic Λ/Σ creation on the Ξ− multiplicity in subthreshold proton–nucleus collisions

Abstract We present an analysis of Ξ − baryon production in subthreshold proton–nucleus ( p + A ) collisions in the framework of a BUU type transport model. We propose a new mechanism for Ξ production in the collision of a secondary Λ or Σ hyperon and a nucleon from the target nucleus. We find that the Ξ − multiplicity in p + A collisions is sensitive to the angular distribution of hyperon production in the primary N + N collision. Using reasonable assumptions on the unknown elementary cross sections we are able to reproduce the Ξ − multiplicity and the Ξ − / ( Λ + Σ 0 ) ratio obtained in the HADES experiment in p+Nb collisions at s N N = 3.2 GeV energy.

Dilepton and

Abstract.We argue that the NICA fixed-target experiment will be able to provide very important new experimental data on dilepton and

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