arXiv subjects

B. Tomasik

Publications and source records attributed to B. Tomasik.

13 recordsLinked to original sources

arXiv2015

Multistrangeness in Heavy-Ion Collisions

We discuss strangeness production in heavy-ion collisions in the broad energy range --- from SIS energies through AGS-SPS-RHIC and upto LHC energies. On several examples we demonstrate how the strange particle production can reveal information about the collision dynamics and about possible modifications of particle properties in medium. In particular the production of hadrons containing two and more strange quarks, like $Ξ$ and $Ω$ baryons, or a $ϕ$ meson is of interest. We conduct our discussion in the framework of the minimal statistical model, in which the total strangeness yield is fixed by the $K^+$ multiplicity. It is emphasized that in collisions with a small number of produced strange particles, the exact strangeness conservation in each collision event must be explicitly preserved.

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arXiv2012

Strangeness Balance in HADES Experiments and the Xi- Enhancement

HADES data on a strangeness production in Ar+KCl collisions at 1.76A GeV are analyzed within a minimal statistical model. The total negative strangeness content is fixed by the observed K^+ multiplicities on event-by-event basis. Particles with negative strangeness are assumed to remain in chemical equilibrium with themselves and in thermal equilibrium with the environment until a common freeze-out. Exact strangeness conservation in each collision event is explicitly preserved. This implies that Xi baryons can be released only in events where two or more kaons are produced. An increase of the fireball volume due to application of a centrality trigger in HADES experiments is taken into account. We find that experimental ratios of K-/K+, Lambda/K+ and Sigma/K+ can be satisfactorily described provided in-medium potentials are taken into account. However, the calculated Xi-/Lambda/K+ ratio proves to be significantly smaller compared to the measured value (8 times lower than the experimental median value and 3 times lower than the lower error bar). Various scenarios to explain observed Xi enhancement are discussed. Arguments are given in favor of the Xi production in direct reactions. The rates of the possible production processes are estimated and compared.

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arXiv2011

Oscillating HBT radii and the time evolution of the source - sqrt(s_NN) = 200 GeV Au+Au data analyzed with azimuthally sensitive Buda-Lund hydro model

Identified particle spectra of pions, kaons and (anti)protons, and elliptic flow and azimuthal dependence of Bose-Einstein or HBT correlations of identified pions in sqrt(s_NN) = 200 GeV Au+Au collisions is analyzed simultaneously using an ellipsoidally symmetric generalization of the Buda-Lund hydrodynamical model. The transverse flow is found to be faster in the reaction plane than out of plane, which results in a reaction zone that gets slightly more elongated in-plane than out of plane.

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arXiv2011

Catalytic Reactions in Heavy-ion Collisions

We discuss a new type of reactions of a phi meson production on hyperons, pi Y--> phi Y and anti-kaons bar-K N --> phi Y. These reactions are not suppressed according to Okubo-Zweig-Iizuka rule and can be a new efficient source of phi mesons in a nucleus-nucleus collision. We discuss how these reactions can affect the centrality dependence and the rapidity distributions of the phi yield.

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arXiv2010

Spectra, elliptic flow and azimuthally sensitive HBT radii from Buda-Lund model for sqrt(s(NN)) = 200 GeV Au+Au collisions

We present calculations of elliptic flow and azimuthal dependence of correlation radii in the ellipsoidally symmetric generalization of the Buda-Lund hydrodynamic model of hadron production in high-energy nuclear collisions. We compare them to data from RHIC by simultaneous fits to azimuthally integrated invariant spectra of pions, kaons and protons-antiprotons measured by PHENIX in Au+Au reactions at center of mass energy of 200 AGeV. STAR data were used for azimuthally sensitive two-particle correlation function radii and for the transverse momentum dependence of the elliptic flow parameter v2. We have found that the transverse flow is faster in the reaction plane then out of plane, which results in a reaction zone that gets slightly more elongated in-plane than out of plane. The model parameters extracted from the fits are shown and discussed.

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arXiv2009

Catalytic phi meson production in heavy-ion collisions

The phi meson production on hyperons, pi Y --> phi Y and anti-kaons bar-K N--> phi Y is argued to be a new efficient source of phi mesons in a nucleus-nucleus collision. These reactions are not suppressed according to Okubo-Zweig-Izuka rule in contrast to the processes with non-strange particles in the entrance channels, pi B and BB with B=N,Delta. A rough estimate of the cross sections within a simple hadronic model shows that the cross sections of pi Y-->phi Y and bar-K N-->phi Y reactions can exceed that of the pi N--> phi N reaction by factors 50 and 60, respectively. In the hadrochemical model for nucleus-nucleus collisions at SIS and lower AGS energies we calculate the evolution of strange particle populations and phi meson production rate due to the new processes. It is found that the catalytic reactions can be operative if the maximal temperature in nucleus-nucleus collisions is larger than 130 MeV and the collision time is larger than 10 fm. A possible influence of the catalytic reactions on the centrality dependence of the phi yield at AGS energies and the phi rapidity distributions at SPS energies is discussed.

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arXiv2007

Non-equilibrium Phase Transitions in Ultrarelativistic Nuclear Collisions

Highly excited nuclear matter created in ultrarelativistic heavy-ion collisions possibly reaches the phase of quark deconfinement. It quickly cools down and hadronises. We explain that the process of hadronisation may likely be connected with disintegration into fragments. Observable signals of such a scenario are proposed.

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arXiv2007

Study of event-by-event fluctuations in heavy ion collisions

We propose Kolmogorov-Smirnov test as a means for recognising event-by-event fluctuations of rapidity distributions in relativistic heavy ion collisions. Such fluctuations may be induced by the spinodal decomposition of the rapidly expanding system during the 1st order quark-hadron phase transition.

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arXiv1999

Universal pion freeze-out phase-space density

Results on the pion phase-space density at freeze-out in sulphur-nucleus, Pb-Pb and pi-p collisions at the CERN SPS are presented. All heavy-ion reactions are consistent with the thermal Bose-Einstein distribution f=1/[exp(E/T)-1] at T ~ 120 MeV, modified for radial expansion. pi-p data are also consistent with f, but at T ~ 180 MeV and without radial flow.

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arXiv1997

Yano-Koonin-Podgoretskii Parametrisation of the Hanbury Brown-Twiss Correlator

The Yano-Koonin-Podgoretskii (YKP) parametrisation of Hanbury Brown-Twiss (HBT) two-particle correlation functions opens new strategies for extracting the emission duration and testing the longitudinal expansion in heavy-ion collisions. Based on the recently derived model-independent expressions, we present a detailed parameter study of the YKP parameters for a finite, hydrodynamically expanding source model of heavy-ion collisions. For the class of models studied here, we show that the three YKP radius parameters have an interpretation as longitudinal extension, transverse extension and emission duration of the source in the YKP frame. This frame is specified by the fourth fit parameter, the Yano-Koonin velocity which describes to a good approximation the velocity of the fluid element with highest emissivity and allows to test for the longitudinal expansion of the source. Deviations from this interpretation of the YKP parameters are discussed quantitatively.

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arXiv1997

Space-time Characteristics of the Fireball from HBT Interferometry

We present the Yano-Koonin-Podgoretskii parametrisation of the correlation function. Compared to the conventionally used Cartesian parametrisation, this one provides more straightforward measurement of the duration of the emission process in the fireball and a clearer signal of the longitudinal expansion, which is expected in ulrarelativistic heavy ion collisions.

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arXiv1996

Kaon Interferometry

Two-kaon and two-pion correlation functions for an expanding thermalized source are compared. In the Yano-Koonin-Podgoretskii parametrization of the correlation function, the HBT radius parameters are shown to obey M_\bot- scaling in the absence of collective transverse flow. This scaling is broken by transverse flow. An accurate comparison of pion and kaon correlations can thus resolve issue whether the observed M_\bot-dependence of the transverse radius parameter is due to transverse collective flow or other transverse gradients. Effects from resonance decays are shortly discussed.

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arXiv1996

Lifetimes and Sizes from Two-Particle Correlation Functions

We discuss the Yano-Koonin-Podgoretskii (YKP) parametrization of the two-particle correlation function for azimuthally symmetric expanding sources. We derive model-independent expressions for the YKP fit parameters and discuss their physical interpretation. We use them to evaluate the YKP fit parameters and their momentum dependence for a simple model for the emission function and propose new strategies for extracting the source lifetime. Longitudinal expansion of the source can be seen directly in the rapidity dependence of the Yano-Koonin velocity.

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