arXiv subjects

Boris Tomášik

Publications and source records attributed to Boris Tomášik.

14 recordsLinked to original sources

arXiv2021

Anisotropic flow decorrelation in heavy-ion collisions with event-by-event viscous hydrodynamics

Decorrelation of the elliptic flow in rapidity is calculated within a hybrid approach which includes event-by-event viscous fluid dynamics and final state hadronic cascade model. The simulations are performed for Au+Au collisions at center-of-mass collision energies of 27 and 200 GeV per nucleon pair, as well as various colliding systems at 72 GeV per nucleon pair. Initial conditions determined by an extended Monte Carlo Glauber model show better agreement with experimental data than initial conditions from the UrQMD transport model. We show how the observed decorrelation is connected with the decorrelation of initial state spatial anisotropies. We also study how the effect is increased by the final state hadronic cascade.

nucl-th↗

arXiv2021

A benchmark of initial state models for heavy-ion collisions at $\sqrt{s_{_{\rm NN}}}=$ 27 and 62 GeV

Description of relativistic heavy-ion collisions at the energies of RHIC Beam Energy Scan program with fluid dynamic approach poses several challenges, one of which being a complex geometry and a longer duration of the pre-hydrodynamic stage. Therefore, existing fluid dynamic models for heavy-ion collisions at the RHIC Beam Energy Scan energies rely on rather complex initial states, such as UrQMD cascade or multi-fluid dynamics. In this study, we show that functionally simpler, non-dynamical initial states can be employed for the fluid dynamical simulations of Au-Au collisions at $\mbox{$\sqrt{s_{_{\rm NN}}}$}=27$ and 62.4~GeV. We adapt the initial states based on Monte Carlo Glauber model (GLISSANDO 2) and $\sqrt{T_A T_B}$ ansatz based on reduced thickness (T$_{\rm R}$ENTo $p=0$), extended into the longitudinal direction and finite baryon density. We find that both initial states, when coupled to a 3D event-by-event viscous fluid dynamic + cascade model, result in an overall fair reproduction of basic experimental data: pseudorapidity distributions, transverse momentum spectra and elliptic flow, at both collision energies. This is a rather surprising, given that the $\sqrt{T_A T_B}$ ansatz is functionally similar to the EKRT and IP-Glasma models, which are successful at much larger energies and rely on a partonic picture of the initial state.

nucl-th↗

arXiv2021

The Shape of the Correlation Function

The correlation function measured in ultrarelativistic nuclear collisions is strongly non-Gaussian. Using two different models we study which effects can influence its shape and how much. In particular, we focus on the parametrizations expressed with the help of Lévy-stable distributions. We show that the Lévy index may deviate substantially from 2 due to non-critical effects such as resonance decays, event-by-event fluctuations and functional dependence on $Q_{LI}$ or similar. We also study the corrections including the first-order Lévy expansion.

nucl-th↗

arXiv2019

Temperatures and chemical potentials at kinetic freeze-out in relativistic heavy ion collisions from coarse grained transport simulations

Using the UrQMD/coarse graining approach we explore the kinetic freeze-out stage in central Au + Au collisions at various energies. These studies allow us to obtain detailed information on the thermodynamic properties (e.g. temperature and chemical potential) of the system during the kinetic decoupling stage. We explore five relevant collision energies in detail, ranging from $\sqrt{s_{NN}}=2.4\,\mathrm{GeV}$ (GSI-SIS) to $\sqrt{s_{NN}}=200\,\mathrm{GeV}$ (RHIC). By adopting a standard Hadron Resonance Gas equation of state, we determine the average temperature $\langle T \rangle$ and the average baryon chemical potential $\langleμ_{\mathrm{B}}\rangle$ on the space-time hyper-surface of last interaction. The results highlight the nature of the kinetic freeze-out as a continuous process. This differential decoupling is an important aspect often missed when summarizing data as single points in the phase diagram as e.g. done in Blast-Wave fits. We compare the key properties of the system derived by using our approach with other models and we briefly review similarities and differences.

hep-ph↗

arXiv2019

The Shape of the Correlation Function

The two-particle correlation function employed in Hanbury-Brown Twiss interferometry and femtoscopy is traditionally parameterized by a Gaussian form. Other forms, however, have also been used, including the somewhat more general Lévy form. Here we consider a variety of effects present in realistic femtoscopic studies which may modify the shape of the correlation function and thereby influence the physical interpretation of a given parameterization.

nucl-th↗

arXiv2019

The Shape of the Correlation Function

The correlation function measured in ultrarelativistic nuclear collisions is non-Gaussian. By making use of models we discuss and assess how much various effects can influence its shape. In particular, we focus on the parametrisations expressed with the help of Lévy-stable distributions. We show that the Lévy index may deviate substantially from 2 due to non-critical effects such as non-spherical shape, resonance decays, event-by-event fluctuations and functional dependence on $Q_{inv}$ or similar.

nucl-th↗

arXiv2019

Event Shape Sorting: prospects and femtoscopy applications

We demonstrate the use of Event Shape Sorting in femtoscopy. The method allows to select events with similar distributions if hadrons in azimuthal angle. We show that also their correlation radii exhibit interesting dependence on azimuthal angle with anisotropies of different orders visible at the same time. We further demonstrate such features of the hadron distribution which can be hardly recognised by Event Shape Engineering, but shows up in Event Shape Sorting. Finally, the influence of statistical fluctuations on sorting is investigated.

nucl-th↗

arXiv2018

Bringing particle physics into classrooms

Exciting scientific results such as the discovery of the Higgs boson offer a great opportunity to engage young people in particle physics. International Particle Physics Masterclasses highlight how high school students across the world can be exposed to real data from CERN's LHC accelerator in a stimulating and productive atmosphere in just a single day.

physics.ed-ph↗

arXiv2016

Higher order anisotropies in the Buda-Lund model: Disentangling flow and density field anisotropies

The Buda-Lund hydro model describes an expanding ellipsoidal fireball, and fits the observed elliptic flow and oscillating HBT radii successfully. Due to fluctuations in energy depositions, the fireball shape however fluctuates on an event-by-event basis. The transverse plane asymmetry can be translated into a series of multipole anisotropy coefficients. These anisotropies then result in measurable momentum-space anisotropies, to be measured with respect to their respective symmetry planes. In this paper we detail an extension of the Buda-Lund model to multipole anisotropies and investigate the resulting flow coefficients and oscillations of HBT radii.

nucl-th↗

arXiv2016

HBT radii from the multipole Buda-Lund model

The Buda-Lund model describes an expanding hydrodynamical system with ellipsoidal symmetry and fits the observed elliptic flow and oscillating HBT radii successfully. The ellipsoidal symmetry can be characterized by the second order harmonics of the transverse momentum distribution, and it can be also observed in the azimuthal oscillation of the HBT radii measured versus the second order reaction plane. The model may have to be changed to describe the experimentally indicated higher order asymmetries. In this paper we detail an extension of the Buda-Lund hydro model to investigate higher order flow harmonics and the triangular dependence of the azimuthally sensitive HBT radii.

hep-ph↗

arXiv2016

Generation of random deviates for relativistic quantum-statistical distributions

We provide an algorithm for generation of momenta (or energies) of relativistic particles according to the relativistic Bose-Einstein or Fermi-Dirac distributions. The algorithm uses rejection method with effectively selected comparison function so that the acceptance rate of the generated values is always better than 0.9. It might find its use in Monte-Carlo generators of particles from reactions in high-energy physics.

physics.comp-ph↗

arXiv2012

Influence of momentum and charge conservation on azimuthally sensitive correlations

Charge neutralisation procedure based on a Markov chain Monte Carlo algorithm is applied to a system of generated hadrons. The algorithm changes the charge of a randomly picked particle by shifting it within its isomultiplet. For baryons changes in both electric charge and baryon number are applied and the algorithm leads to charge and baryon number neutralisation. The procedure can thus be used to study the effects of the local charge and baryon number conservation. We attempt to study these together with the local momentum conservation and their effect on azimuthal correlator observable sensitive to local C and CP violation in quark-gluon plasma.

nucl-th↗

arXiv2009

Bulk viscosity-driven freeze-out in heavy ion collisions

We give an review the HBT puzzle, and argue that its resolution requires the introduction of new physics close to the phase transition scale. We argue that a candidate for this new physics is bulk viscosity, recently postulated to peak, and even diverge, close to the phase transition temperature. We show that such a viscosity peak can force the system created in heavy ion collisions to become unstable, and filament into fragments whose size is weakly dependent on the global size of the system, thereby triggering freeze-out.

nucl-th↗

arXiv2008

Freeze-out by bulk viscosity driven instabilities

We describe a new scenario (first introduced in [G. Torrieri, B. Tomášik and I. Mishustin, Phys. Rev. C \textbf{77}, 034903 (2008)]) for freezeout in heavy ion collisions that could solve the lingering problems associated with the so-called HBT puzzle. We argue that bulk viscosity increases as $T$ approaches $T_c$. The fluid {then} becomes unstable against small perturbations, and fragments into clusters of a size much smaller than the total size of the system. These clusters maintain the pre-existing outward-going flow, as a spray of droplets, but develop no flow of their own, and hadronize by evaporation. We show that this scenario can explain HBT data and suggest how it can be experimentally tested.

hep-ph↗