arXiv subjects

Elena Bratkovskaya

Publications and source records attributed to Elena Bratkovskaya.

At least 37 records · Page 2Linked to original sources

arXiv2025

Transport coefficients of heavy quarks by elastic and radiative scatterings in the strongly interacting quark-gluon plasma

We extend our investigation of heavy quark transport coefficients in the effective dynamical quasiparticle model (DQPM) -- which reproduces nonperturbative QCD phenomena in the strongly interacting quark-gluon plasma (sQGP) according to lattice QCD data -- by including inelastic $2 \to 3$ processes with massive gluon radiation, in addition to elastic $2 \to 2$ parton scattering. Both elastic and inelastic reactions are evaluated at leading order using DQPM-based effective propagators and vertices, accounting for all channels and their interferences. Based on the obtained matrix elements, we calculate various observables connected to a charm quark. First, we calculate the total cross section of a charm quark with the medium partons as functions of temperature and collision energy. Second, we obtain the drag $\mathcal{A}$ coefficient and $\hat{q}$ coefficient of a charm quark as functions of temperature and momentum and also compare our results with those obtained using the Zakharov model for the momentum-dependent strong coupling for the elastic and radiative vertices with a heavy quark, highlighting the importance of the choice of the strong coupling in the determination of transport coefficients. Third, we calculate the spatial diffusion coefficient of a charm quark and compare our results with those obtained using other approaches. Finally, we explore the mass dependence of the diffusion coefficient by comparing the results for charm quark, bottom quark, and infinitely-heavy quark. We found that inelastic processes can play a significant role in the determination of the transport coefficients at large transverse momenta, but are strongly suppressed at low transverse momenta.

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arXiv2025

Electromagnetic emission from strongly interacting hadronic and partonic matter created in heavy-ion collisions

We investigate dilepton production in heavy-ion, proton-proton, and proton-nucleus collisions from low energies of 1 AGeV (SIS) to ultra-relativistic energies (LHC) using the Parton-Hadron-String Dynamics (PHSD) transport approach. PHSD is a microscopic, non-equilibrium approach that integrates hadronic and partonic degrees of freedom, providing a comprehensive description of relativistic heavy-ion collisions from initial nucleon-nucleon interactions to quark-gluon plasma (QGP) formation, hadronization, and final-state interactions. Key dilepton sources in PHSD include hadronic decays, bremsstrahlung, QGP radiation ($q+\bar q \to e^+e^-$, \ $q+\bar q \to g+ e^+e^-$, \ $q+g \to q+ e^+e^-$), primary Drell-Yan production, and semileptonic decays of correlated charm and bottom pairs. PHSD well describes dilepton data from HADES, STAR, and ALICE experiments. We examine in-medium effects, such as the vector meson spectral function broadening, and present the excitation function for the dilepton "excess" in the invariant mass range $0.4<M_{ee}<0.75$ GeV/c$^2$. For the first time we report on the baryon chemical potential $μ_B$-dependence of the QGP radiation calculated on a basis of the Dynamical-Quasi-Particle Model (DQPM) in PHSD. The influence of $μ_B$ on the QGP yield grows at lower collision energies, where $μ_B$ becomes large, however, its impact on the total dilepton spectra is small due to the lowering of the QGP volume with decreasing energy. The excitation function of QGP dileptons, is presented versus correlated charm, confirming that the QGP radiation overshines charm contributions at $\sqrt{s} \simeq 25-30$ GeV in central Au+Au collisions, providing access to thermal QGP dileptons at BES RHIC and FAIR.

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arXiv2025

The quest for the quark-gluon plasma from the perspective of dynamical models of relativistic heavy-ion collisions

The physics of heavy-ion collisions is one of the most exciting and challenging directions of science for the last four decades. On the theoretical side one deals with a non-abelian field theory, while on the experimental side today's largest accelerators are needed to enable these studies. The discovery of a new stage of matter - called the quark-gluon plasma (QGP) - and the study of its properties is one of the major achievements of modern physics. In this contribution we briefly review the history of theoretical descriptions of heavy-ion collisions based on dynamical models, focusing on the personal experiences in this inspiring field.

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arXiv2025

Exploring jet transport coefficients by elastic scattering in the strongly interacting quark-gluon plasma

We study the interaction of leading jet partons in a strongly interacting quark-gluon plasma (sQGP) medium based on the effective dynamical quasi-particle model (DQPM). The DQPM describes the non-perturbative nature of the sQGP at finite temperature $T$ and baryon chemical potential $μ_B$ based on a propagator representation of massive off-shell partons (quarks and gluons) whose properties (characterized by spectral functions with $T,μ_B$ dependent masses and widths) are adjusted to reproduce the lQCD EoS for the QGP in thermodynamic equilibrium. We present the results for the jet transport coefficients, i.e. the transverse momentum transfer squared per unit length $\hat{q}$ as well as the energy loss per unit length $ΔE =dE/dx$, in the QGP and investigate their dependence on the temperature $T$ and baryon chemical potential $μ_B$ as well as on jet properties such as the leading jet parton momentum, mass, flavor, and the choice of the strong coupling constant. In this first study only elastic scattering processes of a leading jet parton with the sQGP partons are explored discarding presently the radiative processes (such as gluon Bremsstrahlung). We present a comparison of our results for the elastic energy loss in the sQGP medium with the pQCD results obtained by the BAMPS and LBT models as well as with other theoretical approaches such as lattice QCD and the LO-HTL and also with estimates of $\hat{q}/T^3$ by the color string percolation model (CSPM) and the JET and JETSCAPE Collaborations based on a comparison of hydrodynamical calculations with experimental heavy-ion data.

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arXiv2025

Exploring jet transport coefficients by elastic and radiative scatterings in the strongly interacting quark-gluon plasma

We investigate the interaction of leading jet partons within a strongly interacting quark-gluon plasma (sQGP) medium, using the effective dynamical quasiparticle model (DQPM). The DQPM offers a description of the sQGP's non-perturbative nature at finite temperature $T$ and baryon chemical potential $μ_B$ through a propagator representation of massive off-shell partons (quarks and gluons). These partons are characterized by spectral functions with $T,μ_B$ dependent masses and widths, adjusted to reproduce the lattice Quantum Chromodynamics (lQCD) equation-of-state (EoS) for the QGP in thermodynamic equilibrium. Our focus lies on examining the jet transport coefficients by elastic scattering in sQGP, specifically the transverse momentum transfer squared per unit length denoted as $\hat{q}$, within the QGP. Furthermore, we investigate the dependence of these coefficients on both the medium temperature $T$ and the jet parton energy. By studying the jet transport coefficients and their relationship to temperature and parton energy, we aim to gain insights into the dynamics of jet propagation in the strongly interacting quark-gluon plasma medium.

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arXiv2025

Transport properties of the strongly interacting quark-gluon plasma

We investigate the transport properties of the strongly interacting quark-gluon plasma (sQGP) by comparing the role of elastic and inelastic (radiative) processes in the sQGP medium within the effective dynamical quasi-particle model (DQPM), constructed for the description of non-perturbative quantum chromodynamic (QCD) phenomena of the sQGP in line with the lattice QCD (lQCD) equation of state. First, we present the results for the energy and temperature dependencies of the total radiative cross sections and compare them to the corresponding elastic cross sections. Second, we perform a calculation of the interaction rate and relaxation time of radiative versus elastic scatterings. Finally, we obtain the jet transport coefficient $\hat{q}$ and investigate its dependence on the choice of the strong coupling in thermal, jet parton and radiative vertices.

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arXiv2025

Inelastic and elastic parton scatterings in the strongly interacting quark-gluon plasma

We investigate the role of inelastic processes in the strongly interacting quark-gluon plasma (sQGP) based on the effective dynamical quasi-particle model (DQPM). In the DQPM the non-perturbative properties of the sQGP at finite temperature $T$ and baryon chemical potential $μ_B$ are described in terms of strongly interacting off-shell partons (quarks and gluons) with dynamically generated spectral functions whose properties are adjusted to reproduce the lQCD EoS for the QGP in thermodynamic equilibrium. For the first time the massive gluon radiation processes from the off-shell quark-quark ($q+q$) and quark-gluon ($q+g$) scatterings are calculated explicitly within leading order Feynman diagrams with effective propagators and vertices from the DQPM without any further approximations. We present the results for the energy and temperature dependencies of the total and differential radiative cross sections and compare them to the corresponding elastic cross sections. We show that our results reproduce the pQCD calculations in the limit of zero masses and widths of quasiparticles. Also we study the $μ_B$ dependence of the inelastic cross sections. Moreover, we present estimates for the transition rate and relaxation time of radiative versus elastic scatterings in the sQGP.

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arXiv2025

Hadronization of Heavy Quarks

Heavy-flavor hadrons produced in ultra-relativistic heavy-ion collisions are a sensitive probe for studying hadronization mechanisms of the quark-gluon-plasma. In this work, we survey how different transport models for the simulation of heavy-quark diffusion through a quark-gluon plasma in heavy-ion collisions implement hadronization and how this affects final-state observables. Utilizing the same input charm-quark distribution in all models at the hadronization transition, we find that the transverse-momentum dependence of the nuclear modification factor of various charm hadron species has significant sensitivity to the hadronization scheme. In addition, the charm-hadron elliptic flow exhibits a nontrivial dependence on the elliptic flow of the hadronizing partonic medium.

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arXiv2025

Thermal production of charm quarks in relativistic heavy-ion collisions

We investigate the thermal production of charm quarks in the strongly interacting quark-gluon plasma (sQGP) created in heavy-ion collisions at relativistic energies. Our study is based on the off-shell parton-hadron-string dynamics (PHSD) transport approach describing the full time evolution of heavy-ion collisions on a microscopic basis with hadronic and partonic degrees of freedom. The sQGP is realized within the effective dynamical quasi-particle model (DQPM) which is adjusted to reproduce the lattice QCD results for the thermodynamic observables of the sQGP. Relying on the fact that the DQPM successfully describes the spatial diffusion coefficients $D_s$ from the lQCD, which control the interaction of charm quarks with thermal partons (expressed in terms of strongly interacting off-shell quasiparticles), we evaluate the production of charm quark pairs through the rotation of Feynman diagrams such that the incoming charm quark and outgoing light parton in elastic scattering diagrams are exchanged. The charm quark annihilation is realized by detailed balance. We find that the number of produced thermal charm quark pairs strongly depends on the charm quark mass in the QGP. While for the heavy charm quarks of mass $m_c=1.8$ GeV it is subdominant compared to the primary charm production by binary nucleon-nucleon collisions at RHIC and LHC energies, the numbers of primary and thermal charm quarks become comparable for a smaller (bare) $m_c=1.2$ GeV. Compared with the experimental data on the $R_{\rm AA}$ of $D$-mesons in heavy-ion collisions at RHIC and LHC energies, it is more favorable for charm quarks in the QGP to gain additional mass due to thermal effects rather than to have a low bare mass.

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arXiv2025

Jet transport coefficients by elastic and radiative scatterings in the strongly interacting quark-gluon plasma

We extend the investigation on jet transport coefficients within the effective Dynamical QuasiParticle Model (DQPM) -- constructed for the description of non-perturbative QCD phenomena of the strongly interacting quark-gluon plasma (sQGP) in line with the lattice QCD equation-of-state -- by accounting for inelastic $2\to 3$ reactions with gluon radiation additionally to the elastic scattering of partons. The elastic and inelastic reactions are calculated explicitly within leading-order Feynman diagrams with effective propagators and vertices from the DQPM by accounting for all channels and their interferences. We present the results for the jet transport coefficients such as the transverse momentum transfer squared $\hat{q}$ per unit length as well as the energy loss $ΔE = dE/dx$ per unit length in the sQGP and investigate their dependence on the temperature $T$ and momentum of the jet parton depending on the choice of the strong coupling constant $α_s$ in thermal, jet parton and radiative vertices. For the latter we consider different scenarios used in the literature and find a very strong dependence of $\hat q$ and $ΔE$ on the choice of $α_s$. Moreover, we explore the relation of $\hat{q}/T^3$ to the ratio of specific shear viscosity to entropy density $η/s$ and show that the ratio $T^3/\hat{q}$ to $η/s$ has a strong $T$ dependence -- especially when approaching to $T_c$ -- on the choice of $α_s$ in scattering vertices.

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arXiv2024

Exploring Dark Photon Production and Kinetic Mixing Constraints in Heavy-Ion Collisions

Vector $U$-bosons, often referred to as 'dark photons', are potential candidates for mediating dark matter interactions. In this study, we outline a procedure to derive theoretical constraints on the upper bound of the kinetic mixing parameter $ε^2(M_U)$ using dilepton data from heavy-ion from SIS to RHIC energies. The analysis is based on the microscopic Parton-Hadron-String Dynamics (PHSD) transport model, which successfully reproduces the measured dilepton spectra in $p+p$, $p+A$, and $A+A$ collisions. Besides the dilepton channels resulting from interactions and decays of Standard Model particles (such as mesons and baryons), we extend the PHSD approach to include the decay of hypothetical $U$-bosons into dileptons, $U \to e^+ e^-$. The production of these $U$-bosons occurs via Dalitz decays of pions, $η$-mesons, $ω$-mesons, Delta resonances, as well as from the decays of vector mesons and $K^+$ mesons. This analysis provides an upper limit on $ε^2(M_U)$ and offers insights into the accuracy required for future experimental searches for dark photons through dilepton experiments.

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arXiv2024

Cluster and anti-cluster production in heavy-ion collisions and pA reactions

We investigate light cluster and anti-cluster production in heavy-ion collisions from SIS to RHIC energies within the Parton-Hadron-Quantum-Molecular Dynamics (PHQMD) microscopic transport approach which propagates (anti-)baryons using n-body QMD dynamics. In PHQMD the clusters are formed dynamically by potential interactions between baryons - and recognized by the Minimum Spanning Tree (MST) algorithm - as well as by kinetic reactions in case of deuterons. We present the novel PHQMD results for different observables such as excitation functions of the multiplicity of deuterons, anti-deuterons and tritons, as well as their transverse momentum spectra. Moreover, we investigate the system size dependence of proton and deuteron production in p+A collisions and show the PHQMD results for p+A collisions (A = Be, Al, Cu, Au) at 14 AGeV/c, as well as for asymmetric Au+A collisions (A = Al, Cu, Pb) at a bombarding energy of about 10 AGeV.

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arXiv2024

Search for dark photons in heavy-ion collisions

The vector $U$-bosons, or so called 'dark photons', are one of the possible candidates for the dark matter mediators. We present a procedure to derive theoretical constraints on the upper limit of kinetic mixing parameter $ε^2(M_U)$ from heavy-ion as well as $p+p$ and $p+A$ dilepton data from SIS to LHC energies. Our study is based on the microscopic Parton-Hadron-String Dynamics (PHSD) transport approach which reproduces the measured dilepton spectra in $p+p$, $p+A$ and $A+A$ collisions well. In addition to the different dilepton channels originating from interactions and decays of ordinary Standard Model matter particles (mesons and baryons), we incorporate in the PHSD the decay of hypothetical $U$-bosons to dileptons, $U \to e^+ e^-$, where the $U$-bosons themselves are produced by the Dalitz decay of pions, $η$-mesons, Delta resonances as well as by vector meson and $K^+$ decays. This analysis provides the upper limit on the $ε^2(M_U)$ and can also help to estimate the requested accuracy for future experimental searches of 'light' dark photons by dilepton experiments.

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arXiv2024

Quarkonium production in pp and heavy-ion collisions

We describe bottomonium production not only in pp collisions but also in heavy-ion collisions by using the Remler's formalism where quarkonium density operator is applied to all possible combination of heavy quark and heavy antiquark pairs. In pp collisions heavy (anti)quark momentum is provided by the PYTHIA event generator after rescaling $p_T$ and rapidity to imitate the FONLL calculations. Then spatial separation between heavy quark and heavy antiquark is introduced based on the uncertainty principle. In heavy-ion collisions quarkonium wavefunction changes with temperature assuming heavy quark potential equals the free energy of heavy quark and heavy antiquark system in heat bath. The density operator is updated whenever heavy quark or heavy antiquark scatters in QGP produced in heavy-ion collisions. Our results are consistent with the experimental data from ALICE and CMS Collaborations assuming that the interaction rate of heavy (anti)quark in quarkonium is suppressed to 10 \% that of unbound heavy (anti)quark. We also find that off-diagonal recombination of bottomonium barely happens even in Pb+Pb collisions at $\sqrt{s}=5.02$ TeV.

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arXiv2024

Production and in-medium modification of $ϕ$ mesons in proton-nucleus reactions from a transport approach

Production and in-medium modification of hidden strange $ϕ$ mesons are studied in proton-nucleus reactions - p+C, p+Cu and p+Pb - at 12 GeV/c, partially measured by the KEK E325 collaboration via the dilepton decay mode. This work is based on the off-shell microscopic Parton-Hadron-String Dynamics (PHSD) transport approach, which provides the dynamical description of strongly interacting hadronic and partonic degrees of freedom in dense matter, and especially makes it possible to simulate in-medium off-shell dynamics of the $ϕ$ meson in the reactions studied. Different in-medium scenarios for the modification of the $ϕ$ meson spectral function in nuclear matter are investigated: i) dropping pole mass, ii) collisional broadening and iii) simultaneous dropping pole mass and collisional broadening. Even though the $ϕ$ meson production in p+A reactions occurs only at densities around or below normal nuclear matter density $ρ_0$, we find visible modifications of the generated dilepton spectra for the in-medium scenarios compared to the vacuum distribution.

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arXiv2024

Finite density QCD equation of state: critical point and lattice-based $T'$-expansion

We present a novel construction of the QCD equation of state (EoS) at finite baryon density. Our work combines a recently proposed resummation scheme for lattice QCD results with the universal critical behavior at the QCD critical point. This allows us to obtain a family of equations of state in the range $0 \leq μ_B \leq 700$ MeV and 25 MeV $\leq T \leq 800$ MeV, which match lattice QCD results near $μ_B=0$ while featuring a critical point in the 3D Ising model universality class. The position of the critical point can be chosen within the range accessible to beam-energy scan heavy-ion collision experiments. The strength of the singularity and the shape of the critical region are parameterized using a standard parameter set. We impose stability and causality constraints and discuss the available ranges of critical point parameter choices, finding that they extend beyond earlier parametric QCD EoS proposals. We present thermodynamic observables, including baryon density, pressure, entropy density, energy density, baryon susceptibility and speed of sound, that cover a wide range in the QCD phase diagram relevant for experimental exploration.

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arXiv2024

Lattice-based equation of state with 3D Ising critical point

The BEST Collaboration equation of state combining lattice data with the 3D Ising critical point encounters limitations due to the truncated Taylor expansion up to $\frac{μ_B}{T} \sim 2.5$. This truncation consequently restricts its applicability at high densities. Through a resummation scheme, the lattice results have been extended to $\frac{μ_B}{T} = 3.5$. In this article, we amalgamate these ideas with the 3D-Ising model, yielding a family of equations of state valid up to $μ_B=700 \text{MeV}$ with the correct critical behavior. Our equations of state feature tunable parameters, providing a stable and causal framework-a crucial tool for hydrodynamics simulations.

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arXiv2024

Dense Nuclear Matter Equation of State from Heavy-Ion Collisions

The nuclear equation of state (EOS) is at the center of numerous theoretical and experimental efforts in nuclear physics. With advances in microscopic theories for nuclear interactions, the availability of experiments probing nuclear matter under conditions not reached before, endeavors to develop sophisticated and reliable transport simulations to interpret these experiments, and the advent of multi-messenger astronomy, the next decade will bring new opportunities for determining the nuclear matter EOS, elucidating its dependence on density, temperature, and isospin asymmetry. Among controlled terrestrial experiments, collisions of heavy nuclei at intermediate beam energies (from a few tens of MeV/nucleon to about 25 GeV/nucleon in the fixed-target frame) probe the widest ranges of baryon density and temperature, enabling studies of nuclear matter from a few tenths to about 5 times the nuclear saturation density and for temperatures from a few to well above a hundred MeV, respectively. Collisions of neutron-rich isotopes further bring the opportunity to probe effects due to the isospin asymmetry. However, capitalizing on the enormous scientific effort aimed at uncovering the dense nuclear matter EOS, both at RHIC and at FRIB as well as at other international facilities, depends on the continued development of state-of-the-art hadronic transport simulations. This white paper highlights the essential role that heavy-ion collision experiments and hadronic transport simulations play in understanding strong interactions in dense nuclear matter, with an emphasis on how these efforts can be used together with microscopic approaches and neutron star studies to uncover the nuclear EOS.

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