arXiv subjects

Boris Tomasik

Publications and source records attributed to Boris Tomasik.

At least 19 recordsLinked to original sources

arXiv2026

$S$-matrix calculation of $BQ$ correlation at finite baryon density

We calculate the baryon number--electric charge susceptibility at non-vanishing baryo-chemical potential within the model of hadron gas where pion-nucleon interaction is accounted for by the $S$-matrix formalism. The susceptibility is largely increased when the chemical potential grows within a phenomenologically relevant interval. The results are then evaluated along the chemical freeze-out line. We also calculate the evolution of the susceptibility in a cooling fireball by making use of the Partial Chemical Equilibrium model.

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arXiv2025

Elliptic flow of deuterons from simulations with hybrid model

Elliptic flow of deuterons is measured on simulated collisions events of Pb+Pb at CMS energy of 2.76 TeV per colliding nucleon pair. We use hybrid model that includes hydrodynamics for the deconfined phase and hadron transport as an afterburner. For deuterons, two production mechanisms are examined: coalescence, and direct thermal production during hadronisation and subsequent transport through the hadronic phase. Differential elliptic flow of deuterons in different centrality bins is evaluated for both implemented production models. In this approach, coalescence describes the experimental data better than direct deuteron production.

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arXiv2024

Excited cluster states: A new source for proton number fluctuations in the high baryon density regime

We calculate the contribution of the decay products of excited nuclear cluster states to the event-by-event fluctuations of protons in the energy range from $\sqrt{s_{NN}}=2-5$~GeV within the statistical model. We find that the inclusion of the excited nuclear clusters yields corrections to all cumulant ratios, ranging from 1\% for ratio of second to first-order cumulant to 100\% for the sixth to second order cumulant towards the lowest inspected energy. As expected the contribution of excited cluster states is most important at low energies $\sqrt{s_{NN}}<3.5$~GeV and becomes negligible at higher collision energies. Especially in light of the expected ultra-high precision data from CBM at FAIR, this new contribution is important to allow for a quantitative comparison with (potentially later available) lattice QCD or effective model results.

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arXiv2024

Simulating collectivity in dense baryon matter with multiple fluids

We report on construction of a modern multi-fluid approach to heavy-ion collisions at FAIR/BES energies (MUFFIN) and show the reproduction of basic experimental observables in Au-Au collisions in the RHIC Beam Energy Scan program. We also show the $p_T$-differential and $p_T$-integrated polarization of (anti-)$\Lambda$ hyperons. In MUFFIN simulations, we observe a strong splitting between polarizations of $\Lambda$ and anti-$\Lambda$. The splitting is driven purely by a finite baryon chemical potential.

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arXiv2024

On elliptic flow and the blast-wave model

Extensions of the blast-wave model for the description of non-central collisions are reviewed and the physics behind them is explained and illustrated. It is shown how the second-order anisotropy in expansion velocity together with the anisotropy in the shape or the density profile of the fireball determine the elliptic flow of the produced hadrons. Ambiguities and limitations of the models are discussed and different models are compared among themselves and with example data. It is concluded that model results should always be compared to $v_2(p_t)$ from several identified species in order to receive meaningful results about the freeze-out stage of the fireball and that even such a comparison may not be conclusive as the models may not be able to reproduce all relevant data.

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arXiv2024

Elliptic flow of deuterons in ultrarelativistic heavy-ion collisions

We calculate the elliptic flow of deuterons in Pb+Pb collisions at 2.76 TeV per colliding nucleon-nucleon pair and show that it can be used to discriminate between direct statistical production and coalescence. The emission from the fireball is parametrized and tuned to reproduce transverse momentum spectra and the elliptic flow of protons and pions. Coalescence leads to higher deuteron elliptic flow than statistical production and agrees better with experimental data. We attribute this observation to the varying size of the nucleon-producing region for the emission in different azimuthal angles.

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arXiv2024

Production of Resonances in Partial Chemical Equilibrium

Within the model of partial chemical equilibrium (PCE) we calculate the multiplicity ratios of selected unstable resonances to given stable species. We focus on those ratios that have been measured either in Pb+Pb collisions at the LHC or in Au+Au collisions at the top RHIC energy. The model provides an interpretation how in an expanding hadronic fireball with decreasing temperature the final numbers of stable hadrons after decays of all resonances remain unchanged. Each stable species acquires its own chemical potential and the resonances are kept in equilibrium with them. Multiplicities of unstable resonances provide a test of this scenario. We observe that the ratios of $K^{*}/K$ and $\rho^0/\pi$ fit reasonably well into the picture of single kinetic freeze-out of the single-particle spectra, but the $\phi$-meson and hyperon resonances are not reproduced by this model.

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arXiv2024

Bridging the gap between cutting-edge science and school: non-formal education in high-energy physics

We report mainly on the global flagship outreach activity in particle physics: the International Particle Physics Masterclasses. It is illustrated on the example of Slovakia and the Czech Republic. The Masterclasses are described and their long-term impact is studied with the help of a survey among former participants. The positive effect of Masterclasses in shifting the attitude towards science is shown. We also discuss the modification of Masterclasses for a pandemic situation. Finally, we present CASCADE projects as a way to foster the interest in a field which has been strongly enhanced by previous experience, e.g., at Masterclasses.

physics.ed-ph↗

arXiv2023

Simulating collectivity in dense baryon matter with multiple fluids

A novel three-fluid dynamical model for simulations of heavy-ion collisions at RHIC Beam Energy Scan programme, called MUFFIN, has been developed. The novelty consists of modular inclusion of the Equation of State, use of hyperbolic coordinates that allow to simulate higher collision energies, and fluctuating initial conditions. The model reproduces rapidity and $p_t$ spectra of collisions from $\sqrt{s_{NN}}$=7.7 to 62.4 GeV. Ideal fluid is assumed, and the elliptic flow is over-predicted, particularly at lower collision energies.

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arXiv2023

On the long-term impact of non-formal learning in particle physics

Since 2005, the global flagship of outreach activities in high-energy physics have been the International Particle Physics Masterclasses. We report on a survey performed among the participants from Slovakia and the Czech Republic, where we have studied the impact of Masterclasses on their further careers and their attitude towards science and especially particle physics. More than a half of our respondents does not work in science or research and development. However, most of them report positive shift in their attitude towards science. A positive nudge to physics career is indicated among those being open to such a possibility.

physics.ed-ph↗

arXiv2023

Next-generation multi-fluid hydrodynamic model for RHIC BES

We have developed a next-generation hybrid event-by-event three-fluid hydrodynamic model, suitable for simulations of heavy-ion collisions in the energy range from few up to tens of GeV per colliding NN pair. At such energies the interpenetration time of the nuclei is of the same order as the lifetime of the system, however this model treats the initial phase hydrodynamically. Thanks to that it is more sensitive to the Equation of State than 1-fluid models with initial states being parametrised or generated by transport approach. Hence, our model is well designed for simulations at collision energies, at which matter in vicinity of the QCD critical endpoint is expected. The construction of the model is explained and basic observables like hadron spectra in rapidity and transverse momentum, as well as elliptic flow are calculated.

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arXiv2022

Resonance production in partial chemical equilibrium

In high energy collisions, a dense, strongly interacting medium could be created, the quark gluon plasma. In rapid expansion, from the soup of quarks and gluons a gas of resonance and stable particles is formed at the chemical freeze-out and after that, as the system cools down, the kinetic freeze-out takes place and interaction between particles ceases. By measuring resonance ratios one could get information about the dominant physical processes in the intermediate temperature ranges, i.e. between the chemical and kinetic freeze-out. These quantities are measured at RHIC and LHC energies. In the present analysis we employ the hadron resonance gas model assuming partial chemical equilibrium to characterize these measured data. We calculate the ratios of several resonances to their stable counterpart and compare these model calculations to available experimental data.

hep-ph↗

arXiv2022

Flow decorrelation in heavy-ion collisions at $\sqrt{s_{_{\rm NN}}}$=27 and 200 GeV with 3D event-by-event viscous hydrodynamics

We present the first calculation of longitudinal decorrelation of anisotropic flow at RHIC Beam Energy Scan (BES) energies using event-by-event viscous hydrodynamic model (vHLLE), with two different initial states (GLISSANDO2 and UrQMD) and hadronic cascade. We investigate the origin of the observed decorrelation by checking separately flow angle and flow magnitude decorrelation and by calculating decorrelation in the initial state eccentricity.

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arXiv2021

Anisotropic flow decorrelation in heavy-ion collisions at RHIC-BES energies with 3D event-by-event viscous hydrodynamics

In the RHIC Beam Energy Scan program, gold nuclei are collided with different collision energies in the range from few to 62.4 GeV. The goals of the program are to explore the onset of QGP creation, locate the critical point of QCD and study dense baryon matter. We report on the first application of Monte Carlo Glauber (GLISSANDO2) and T$_{\rm R}$ENTo $p=0$ initial states extended to 3D for event-by-event viscous fluid dynamic (vHLLE) with hadronic cascade modelling of Au+Au collisions at $\sqrt{s_{_{\rm NN}}}=27$ and 62.4 GeV, which is the upper region of RHIC BES energies. The initial states are extended into both the longitudinal direction and for finite baryon density using simple ansätze. The full energy and baryon charge counting in the initial states is implemented. We show the reproduction of elliptic flow, at both collision energies and with both initial states. We compare it also to the results obtained with UrQMD initial state. Furthermore, we show the results for rapidity decorrelation of elliptic flow $r_2$ at $\sqrt{s_{_{\rm NN}}}=27$ and 200 GeV from the same setup of hydrodynamic calculations with the 3D Monte Carlo Glauber and UrQMD initial states. We discuss the features of the initial states responsible for the magnitude of the observed flow decorrelation.

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arXiv2021

Proton number fluctuations in partial chemical equilibrium

We calculate volume-independent ratios of cumulants of the net-proton number distribution up to sixth order in a fireball that cools down after the chemical freeze-out. A hadron resonance gas model is used together with the assumption of partial chemical equilibrium, which fixes the number of observed stable hadrons after the chemical freeze-out. It is shown that due to only weak departure from the statistical Boltzmann distribution, also the volume-independent ratios of higher-order cumulants of the net-proton number show only weak dependence on the temperature. This observation supports the possibility to measure non-critical cumulants at chemical freeze-out even after subsequent cooling in the hadronic phase. Cumulants of the net-baryon number behave similarly, while those for the kaon number vary more strongly with the temperature. Our results are relevant for the current fluctuation studies of the RHIC-BES runs.

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arXiv2019

Prospects of Event Shape Sorting

Event Shape Sorting is a novel method which is devised to organise a sample of collision events in such a way, that events with similar final state distribution of hadrons end up sorted close to each other. Such events are likely to have evolved similarly. Thus the method allows to focus at finer features of the collision evolution because it would allow for averages over similar events that do not wash away these features. The algorithm is shortly explained. We also point out the distinction of Event Shape Sorting from the well established technique of Event Shape Engineering.

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arXiv2019

Kinetic freeze-out in central heavy-ion collisions between 7.7 and 2760 GeV per nucleon pair

We fit the single-particle $p_t$ spectra of identified pions, kaons, and (anti)protons from central collisions of gold or lead nuclei at energies between 7.7 and 2760~GeV per nucleon pair. Blast wave model with included resonance production and with an assumption of partial chemical equilibrium is used and the fits are performed with the help of a Gaussian emulator process. A kinetic freeze-out temperature is found about 100~MeV for the lowest collision energies and 80~MeV at the LHC. The average transverse expansion velocity grows with increasing $\sqrt{s_{NN}}$ from 0.45 to 0.65. Due to partial chemical equilibrium, the influence of resonance decays on the shape of the $p_t$ spectra for $\sqrt{s_{NN}}$ above 27~GeV is small.

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arXiv2019

Benchmark values for the net proton number fluctuations

We formulate a baseline model for the net-proton number fluctuations in ultrarelativistic heavy-ion collisions. Our model includes total baryon number conservation, fluctuations of the participating nucleon number, limited acceptance, and a possibility that isospin is remembered by the participating wounded nucleons. Most importantly, we formulated the model as consisting of two components: wounded nucleons and the produced nucleon-antinucleon pairs. Those two components have different rapidity distributions. Owing to this feature we obtain also predictions for the rapidity dependence of the cumulants of the net-proton number distribution and their ratios.

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