arXiv subjects

Elena Bratkovskaya

Publications and source records attributed to Elena Bratkovskaya.

At least 55 records · Page 3Linked to original sources

arXiv2024

Bottomonium production in pp and heavy-ion collisions

We study bottomonium $b\bar b$ production in pp collisions as well as in heavy-ion collisions, using a quantal density matrix approach. The initial bottom (anti)quarks are provided by the PYTHIA event generator. We solve the Schrödinger equation for the $b\bar b$ pair, identifying the potential with the free energy, calculated with lattice QCD, to obtain the temperature dependent $b\bar b$ density matrix as well as the dissociation temperature. The formation of bottomonium is given by projection of the bottomonium density matrix onto the density matrix of the system. With this approach we describe the rapidity and transverse momentum distribution of the $Υ$(nS) in pp collisions at $\sqrt{s_{\rm NN}}=$ 5.02 TeV extending a similar calculation for the charmonium states \cite{Song:2017phm}. We employ the Remler formalism to study the $b\bar b$ production in heavy ion collisions in which the heavy quarks scatter elastically with partons from the quark gluon plasma (QGP). The elastic scattering of heavy (anti)quark in QGP is realized by the dynamical quasi-particle model (DQPM) and the expanding QGP is modeled by PHSD. We find that a reduction to 10 \% of the scattering cross section for a (anti)bottom quark with a QGP parton reproduces the experimental data. This suggests that due to color neutrality the scattering cross section of the small $b\bar b$ system with a parton is considerably smaller than twice the bottom-parton scattering cross section.

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arXiv2023

Quarkonium production in high energy $pp$ collisions

We investigate the charmonium and bottomonium production in $pp$ collisions using the Wigner densities formalism. The Wigner density of the quarkonia is approximated by analytical 3-D isotropic harmonic oscillator Wigner densities with the same root-mean-square radius given by the solution of the Schrödinger equation. This approach reproduces quite well the available experimental transverse momentum and rapidity distributions.

hep-ph↗

arXiv2023

Extraction of the microscopic properties of quasi-particles using deep neural networks

We use deep neural networks (DNN) to obtain the microscopic characteristics of partons in terms of dynamical degrees of freedom on the basis of an off-shell quasiparticle description. We aim to infer masses and widths of quasi-gluons, up/down, and strange quarks using constraints on the macroscopic thermodynamic observables obtained by the first-principles calculations lattice QCD. In this work, we use 3 independent dimensionless thermodynamic observables from lQCD for minimization. First, we train our DNN using the DQPM (Dynamical QuasiParticle Model) Ansatz for the masses and widths. Furthermore, we use the DNN capabilities to generalize this Ansatz, to evaluate which quasiparticle characteristics are desirable to describe different thermodynamic functions simultaneously. To evaluate consistently the microscopic properties obtained by the DNN in the case of off-shell quarks and gluons, we compute transport coefficients using the spectral function within Kubo-Zubarev formalism in different setups. In particular, we make a comprehensive comparison in the case of the dimensionless ratios of shear viscosity over entropy density $η/s$ and electric conductivity over temperature $σ_Q/T$, which provide additional constraints for the parameter generalization of the considered models.

hep-ph↗

arXiv2023

Heavy flavor production in the Parton-Hadron-String Dynamics (PHSD)

Relativistic heavy-ion collisions produce a hot and dense nuclear matter, through which one can study the phase diagram of QCD. Open and hidden heavy flavors are promising probes to search for the properties of the hot and dense nuclear matter under extreme conditions. We present how the production and interactions of open and hidden heavy flavors in heavy-ion collisions are realized in the Parton-Hadron-String Dynamics, which is a non-equilibrium microscopic transport approach for the description of the dynamics of strongly interacting hadronic and partonic matter.

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arXiv2023

Radiative energy loss of heavy quark through soft gluon emission in QGP

The Low's theorem is applied to the soft gluon emission from heavy quark scattering in quark-gluon plasma (QGP). The QGP is described by the dynamical quasi-particle model (DQPM) which reproduces the EoS from lQCD at finite temperature and chemical potential. We show that if the emitted gluon is soft and of long wavelength, the scattering amplitude can be factorized into the scattering part and the emission part and the Slavnov-Taylor identities are satisfied in the leading order. Imposing a proper upper limit on the emitted gluon energy, we obtain the scattering cross sections of charm quark as well as the transport coefficients (momentum drag and diffusion) in the QGP with and without gluon emission.

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arXiv2023

Phase Transitions in Particle Physics -- Results and Perspectives from Lattice Quantum Chromo-Dynamics

Phase transitions in a non-perturbative regime can be studied by ab initio Lattice Field Theory methods. The status and future research directions for LFT investigations of Quantum Chromo-Dynamics under extreme conditions are reviewed, including properties of hadrons and of the hypothesized QCD axion as inferred from QCD topology in different phases. We discuss phase transitions in strong interactions in an extended parameter space, and the possibility of model building for Dark Matter and Electro-Weak Symmetry Breaking. Methodological challenges are addressed as well, including new developments in Artificial Intelligence geared towards the identification of different phases and transitions.

hep-lat↗

arXiv2023

Dynamical mechanisms for deuteron production at mid-rapidity in relativistic heavy-ion collisions from SIS to RHIC energies

The understanding of the mechanisms for the production of weakly bound clusters, such as a deuteron $d$, in heavy-ion reactions at mid-rapidity is presently one of the challenging problems which is also known as the "ice in a fire" puzzle. In this study we investigate the dynamical formation of deuterons within the Parton-Hadron-Quantum-Molecular Dynamics (PHQMD) microscopic transport approach and advance two microscopic production mechanisms to describe deuterons in heavy-ion collisions from SIS to RHIC energies: kinetic production by hadronic reactions and potential production by the attractive potential between nucleons. Differently to other studies, for the "kinetic" deuterons we employ the full isospin decomposition of the various $πNN\leftrightarrow πd$, $NNN\leftrightarrow N d$ channels and take into account the finite size properties of the deuteron by means of an excluded volume condition in coordinate space and by the projection onto the deuteron wave function in momentum space. We find that considering the quantum nature of the deuteron in coordinate and momentum space reduces substantially the kinetic deuteron production in a dense medium as encountered in heavy-ion collisions. If we add the "potential" deuterons by applying an advanced Minimum Spanning Tree (aMST) procedure, we obtain good agreement with the available experimental data from SIS energies up to the top RHIC energy.

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arXiv2023

Charmonium production in a thermalizing heat bath

Using the Remler formalism for the creation of composed particles, we study charmonium production both in thermalized and thermalizing boxes, which contain charm and anticharm quarks. The thermalizing box studies include the lowering of the box temperature, the spatial diffusion of charm and anticharm quarks, which are initially confined in the central region, as well as the combination of both, what imitates heavy-ion collisions. Comparing numerical and analytical results we demonstrate that the rate of the original Remler formalism has to be supplemented by two rates to obtain, for $t\to \infty$, results, which are consistent with the statistical model predictions: i) a rate, which takes into account the temperature dependence of the Wigner density of the quarkonium during the expansion and, in the case that a heavy quark potential is not implemented in the Monte Carlo approach, ii) a rate which comes from the change of the relative distance between the heavy quark and antiquark. These results provide the basis for future applications of the Remler formalism to heavy-ion collisions.

hep-ph↗

arXiv2023

Opportunities for new physics searches with heavy ions at colliders

Opportunities for searches for phenomena beyond the Standard Model (BSM) using heavy-ions beams at high energies are outlined. Different BSM searches proposed in the last years in collisions of heavy ions, mostly at the Large Hadron Collider, are summarized. A few concrete selected cases are reviewed including searches for axion-like particles, anomalous $τ$ electromagnetic moments, magnetic monopoles, and dark photons. Expectations for the achievable sensitivities of these searches in the coming years are given. Studies of CP violation in hot and dense QCD matter and connections to ultrahigh-energy cosmic rays physics are also mentioned.

hep-ph↗

arXiv2022

Nonequilibrium effects and transverse spherocity in ultra-relativistic proton-nucleus collisions

We investigate the effects of nonequilibrium dynamics in small colliding systems by comparing a nonequilibrium transport approach, the Parton-Hadron-String-Dynamics (PHSD), with a (2+1)D viscous hydrodynamic model, VISHNew. Focusing on p+Pb collisions at LHC energy, we extract the initial conditions for the hydrodynamic model from PHSD, in order to reduce the impact of the early out-of-equilibrium dynamics and focus on the traces of nonequilibiurm in the ensuing medium evolution. We find that in the transport approach quantities like energy density and bulk viscous pressure are highly inhomogeneous on the transverse plane during the whole evolution, whereas the hydrodynamic simulations dissolve more efficiently the initial spatial irregularities, still keeping a high degree of inhomogeneity due to the smaller size and lifetime of the medium produced in p+Pb collisions with respect to heavy-ion reactions. As a first step that will help to identify the impact of these nonequilibrium effects on final observables in proton-nucleus collisions, we perform an analysis of the transverse spherocity, an event-shape observable able to distinguish between jetty and isotropic configurations of transverse momenta. We found that the spherocity distribution in PHSD is slightly shifted towards the isotropic limit with respect to the hydrodynamic result. Even though this dissimilarity is partially due to the difference in the final charged particle production, it mainly comes from the different description within the two frameworks of the medium produced in small colliding systems. This finding supports the idea that multi-differential measurements, such as those based on event categorization according to multiplicity and spherocity, are useful to study final-state observables in ultrarelativistic proton-nucleus collisions.

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arXiv2022

Midrapidity cluster formation in heavy-ion collisions

We study the production of clusters and hypernuclei at midrapidity employing the Parton-Hadron-Quantum-Molecular-Dynamics (PHQMD) approach, a microscopic n-body transport model based on the QMD propagation of the baryonic degrees of freedom with density dependent 2-body potential interactions. In PHQMD the cluster formation occurs dynamically, caused by the interactions. The clusters are recognized by the Minimum Spanning Tree (MST) algorithm. We present the PHQMD results for cluster and hypernuclei formation in comparison with the available experimental data at relativistic energies. PHQMD allows to study the time evolution of formed clusters and the origin of their production, which helps to understand how such weakly bound objects are formed and survive in the rather dense and hot environment created in heavy-ion collisions. It offers therefore an explanation of the 'ice in the fire' puzzle. To investigate whether this explanation of the 'ice in the fire' puzzle applies only to the MST results we study also the deuterons production by coalescence. We embed MST and coalescence in the PHQMD and UrQMD transport approaches in order to obtain model independent results. We find that both clustering procedures give very similar results for the deuteron observables in the UrQMD as well as in the PHQMD environment. This confirms that our solution for the 'ice in the fire' puzzle is common to MST and coalescence and independent of the transport approach.

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arXiv2022

In-medium effects in $ϕ$ meson production in heavy-ion collisions from subthreshold to relativistic energies

We investigate the hidden strange $ϕ$ meson production in heavy-ion collisions from subthreshold ($E_{kin}\approx 1$ A GeV) to relativistic ($E_{kin}\approx 21$ A TeV) energies as well as its coupling to the open strange mesons (kaons, antikaons) and their productions. Our study is based on the off-shell microscopic Parton-Hadron-String Dynamics (PHSD) transport approach which is applicable for the dynamical description of strongly interacting hadronic and partonic degrees-of-freedom created in heavy-ion collisions. Implementing novel meson-baryon and meson-hyperon production channels for $ϕ$ mesons, calculated within a T-matrix coupled channel approach based on the extended SU(6) chiral effective Lagrangian model, along with the collisional broadening of the $ϕ$-meson in-medium spectral function, we find a substantial enhancement of $ϕ$ meson production in heavy-ion collisions, especially at sub- and near-thresholds. This allows to describe the experimentally observed strong enhancement of the $ϕ/K^-$ ratio at low energies without including hypothetical decays of heavy baryonic resonances to $ϕ$ as in alternative approaches. Moreover, we show that in spite of a stronger contribution from enhanced $ϕ$ to $K^-$ production, the majority of the experimental data for different A+A systems at low energies favor the scenario with in-medium modifications of the kaon and antikaon properties in the hot and dense environment. Moreover, we study the influence of the final state interactions of $K, \bar K$ mesons on the reconstruction of $ϕ$'s by the by invariant mass method.

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arXiv2022

Transport Model Comparison Studies of Intermediate-Energy Heavy-Ion Collisions

Transport models are the main method to obtain physics information from low to relativistic-energy heavy-ion collisions. The Transport Model Evaluation Project (TMEP) has been pursued to test the robustness of transport model predictions in reaching consistent conclusions from the same type of physical model. Calculations under controlled conditions of physical input and set-up were performed with various participating codes. These included both calculations of nuclear matter in a box with periodic boundary conditions, and more realistic calculations of heavy-ion collisions. In this intermediate review, we summarize and discuss the present status of the project. We also provide condensed descriptions of the 26 participating codes, which contributed to some part of the project. These include the major codes in use today. We review the main results of the studies completed so far. They show, that in box calculations the differences between the codes can be well understood and a convergence of the results can be reached. These studies also highlight the systematic differences between the two families of transport codes, known as BUU and QMD type codes. However, when the codes were compared in full heavy-ion collisions using different physical models, as recently for pion production, they still yielded substantially different results. This calls for further comparisons of heavy-ion collisions with controlled models and of box comparisons of important ingredients, like momentum-dependent fields, which are currently underway. We often indicate improved strategies in performing transport simulations and thus provide guidance to code developers. Results of transport simulations of heavy-ion collisions from a given code will have more significance if the code can be validated against benchmark calculations such as the ones summarized in this review.

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arXiv2022

Transport properties and equation-of-state of hot and dense QGP matter near the critical end-point in the phenomenological dynamical quasi-particle model

We extend the effective dynamical quasiparticle model (DQPM) - constructed for the description of non-perturbative QCD phenomena of the strongly interacting quark-gluon plasma (QGP) - to large baryon chemical potentials, $μ_B$, including a critical end-point and a 1st order phase transition. The DQPM description of quarks and gluons is based on partonic propagators with complex selfenergies where the real part of the selfenergies is related to the quasiparticle mass and the imaginary part to a finite width of their spectral functions. In DQPM the determination of complex selfenergies for the partonic degrees of freedom at zero and finite $μ_B$ has been performed by adjusting the entropy density to the lQCD data. The temperature-dependent effective coupling (squared) $g^2(T/T_c)$, as well as the parton effective masses and widths are based on this adjustment. The novel extended dynamical quasiparticle model, named "DQPM-CP", makes it possible to describe thermodynamical and transport properties of quarks and gluons in a wide range of $T$ and $μ_B$, and reproduces the equation-of-state (EoS) of lQCD calculations in the crossover region of finite $T, μ_B$. We apply a scaling ansatz for the strong coupling constant near the CEP, located at ($T^{CEP}$, $μ^{CEP}_B) = (0.100, 0.960)$ GeV. We show the EoS as well as the speed of sound for $T>T_c$ and for a wide range of $μ_B$, which can be of interest for hydrodynamical simulations. Furthermore, we consider two settings for the strange quark chemical potentials (I) $μ_s=μ_B/3$ and (II) $μ_s=0$. The isentropic trajectories of the QGP matter are compared for these two cases. The phase diagram of DQPM-CP is close to PNJL calculations. The leading order pQCD transport coefficients of both approaches differ. This elucidates that the knowledge of the phase diagram alone is not sufficient to describe the dynamical evolution of QGP.

hep-ph↗

arXiv2022

Deuteron Production in Ultra-Relativistic Heavy-Ion Collisions: A Comparison of the Coalescence and the Minimum Spanning Tree Procedure

The formation of deuterons in heavy-ion collisions at relativistic energies is investigated by employing two recently advanced models -- the Minimum Spanning Tree (MST) method and the coalescence model by embedding them in the PHQMD and the UrQMD transport approaches. While the coalescence mechanism combines nucleons into deuterons at the kinetic freeze-out hypersurface, the MST identifies the clusters during the different stages of time evolution. We find that both clustering procedures give very similar results for the deuteron observables in the UrQMD as well as in the PHQMD environment. Moreover, the results agree well with the experimental data on deuteron production in Pb+Pb collisions at $\sqrt{s_{NN}} = 8.8$ GeV (selected for the comparison of the methods and models in this study). A detailed investigation shows that the coordinate space distribution of the produced deuterons differs from that of the free nucleons and other hadrons. Thus, deuterons are not destroyed by additional rescattering.

nucl-th↗

arXiv2021

Cluster and hyper-cluster production in relativistic heavy-ion collisions within the Parton-Hadron-Quantum-Molecular-Dynamics approach

We study cluster and hypernuclei production in heavy-ion collisions at relativistic energies employing the Parton-Hadron-Quantum-Molecular-Dynamics (PHQMD) approach, a microscopic n-body transport model based on the QMD propagation of the baryonic degrees of freedom with density dependent 2-body potential interactions. All other ingredients of PHQMD, including the collision integral and the treatment of the quark-gluon plasma (QGP) phase, are adopted from the Parton-Hadron-String Dynamics (PHSD) approach. In PHQMD the cluster formation occurs dynamically, caused by the interactions. The clusters are recognized by the Minimum Spanning Tree (MST) algorithm. We present the PHQMD results for cluster and hypernuclei formation in comparison with the available experimental data at AGS, SPS, RHIC-BES and RHIC fixed target energies. We also provide predictions on cluster production for the upcoming FAIR and NICA experiments. PHQMD allows to study the time evolution of formed clusters and the origin of their production, which helps to understand how such weakly bound objects are formed and survive in the rather dense and hot environment created in heavy-ion collisions. It offers therefore an explanation of the 'ice in the fire' puzzle.

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arXiv2021

Comparison of heavy ion transport simulations: Ag+Ag collisions at Elab = 1.58 AGeV

We compare the microscopic transport models UrQMD, PHSD, PHQMD, and SMASH to make predictions for the upcoming Ag+Ag data at $E_\mathrm{lab}=1.58$~$A$GeV ($\sqrt{s_\mathrm{NN}}=2.55$~GeV) by the HADES collaboration. We study multiplicities, spectra and effective source temperatures of protons, $π^{\pm,0}$, $K^\pm$, the $η$, $Λ+Σ^0$ and the $Ξ^-$ within these models. Despite variations in the detailed implementation of the dynamics in the different models, the employed transport approaches all show consistent multiplicities of the bulk of investigated hadrons. The main differences are in the $Ξ^-$ production, which is treated differently between UrQMD/SMASH on one side employing high mass resonance states with explicit decays to $\mathrm{Resonance}\rightarrow Ξ+K+K$ in contrast to PHSD/PHQMD which account only non-resonant $Ξ$ production channels. A comparison of the spectra, summarized by effective source temperatures, shows that all models provide similar source temperatures around $T_\mathrm{source}=80-95$~MeV, and show substantial radial flow on the order of $\langle v_T\rangle=0.22c-0.3c$ even for such a small system.

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arXiv2021

Constraints on the kinetic mixing parameter $ε^2$ for the light dark photons from dilepton production in heavy-ion collisions in the few-GeV energy range

The vector $U$-bosons, or so called 'dark photons', are one of the possible candidates for the dark matter mediators. They are supposed to interact with the standard matter via a 'vector portal' due to the $U(1)-U(1)^\prime$ symmetry group mixing which might make them visible in particle and heavy-ion experiments. While there is no confirmed observation of dark photons, the detailed analysis of different experimental data allows to estimate the upper limit for the kinetic mixing parameter $ε^2$ depending on the mass $M_U$ of $U$-bosons which is also unknown. In this study we present theoretical constraints on the upper limit of $ε^2(M_U)$ in the mass range $M_U \le 0.6$ GeV from the comparison of the calculated dilepton spectra with the experimental data from the HADES Collaboration at SIS18 energies where the dark photons are not observed. Our analysis is based on the microscopic Parton-Hadron-String Dynamics (PHSD) transport approach which reproduces well the measured dilepton spectra in $p+p$, $p+A$ and $A+A$ collisions. Additionally to the different dilepton channels originating from interactions and decays of ordinary matter particles (mesons and baryons), we incorporate 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 $π^0\to γU$, $η$-mesons $η\to γU$ and Delta resonances $Δ\to N U$. Our analysis can help to estimate the requested accuracy for future experimental searches of 'light' dark photons by dilepton experiments.

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