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Time evolution of hot and dense nuclear matter produced in central gold-gold collisions at energies between E lab = 10 and 160 AGeV is studied within two transport string models, UrQMD and QGSM. In contrast to the previous studies, here we investigate the macroscopic characteristics of the system before the state of chemical and thermal equilibrium is attained. For all energies in question two interesting observations are made for times starting already from t ≥ 1 fm/c. (1) The matter in the cell expands almost isentropically with nearly constant entropy per baryon. (2) Pressure in the cell appears to be very close to the pressure calculated for equilibrated hadron gas with the same values of energy density, baryon density and strangeness density. The pressure linearly depends on the energy density, P = a (s) ε . Therefore, both observations endorses the formal application of relativistic hydrodynamics from the very early stages of heavy-ion collisions, despite of the fact that the matter in the fireball is out of equilibrium. [ABSTRACT FROM AUTHOR]

The contributions of various effects to correlations of the average multiplicity of particles emitted in the forward hemisphere of heavy-ion collisions with the multiplicity of particles emitted in the backward hemisphere (forward–backward correlations) have been comparatively analyzed. It has been shown that the experimentally observed dependence of the strength of such correlations on the centrality of lead–lead ion collisions at the Large Hadron Collider energy = 2.76 TeV can be reproduced by the HYDJET++ model if the hydrodynamic particle flow, decay of resonances, and production and suppression of high-energy quarks and gluons in hot matter are taken into account. The dominant mechanism of forward–backward correlations for the most central collisions involves the production and fragmentation of quark–gluon jets. [ABSTRACT FROM AUTHOR]

The data on charge balance function in Pb+Pb collisions at center-of-mass energy 2.76 TeV per nucleon pair are analyzed with the HYDJET++ model. For central collisions, the width of the charge balance function at low transverse momentum intervals is larger in the model than in data. An approach, which takes into account the event-by-event charge conservation, has been implemented into the thermal part of the model at the stage of hadron production. This approach implies two particle charge correlations with a certain length and allows to reproduce experimental widths. [ABSTRACT FROM AUTHOR]

The model analysis of particle production in heavy ion collisions depending on number of emission sources (wounded nucleons or partons) at different centralities is performed in a wide collision energy range from RHIC to LHC. The model of wounded partons based on Glauber calculations gives better scaling for the ratio of charged particle multiplicity to the number of wounded constituent partons depending on collision centrality for all considered energies and colliding systems. Also, the eccentricity density distribution in Glauber Monte Carlo framework has been fulfilled for several centrality intervals. Assuming linear dependence between eccentricity and elliptic flow, the eccentricity density distribution is compared with CMS data on flow fluctuations for PbPb collisions at TeV data. For centralities less than 35 the probability density distribution with wounded partons better describes experimental data. For more peripheral collisions () both models describe data satisfactorily. [ABSTRACT FROM AUTHOR]

The HYDJET event generator is a phenomenological model of heavy-ion collisions that treats the collision process as a combination of a soft hydro-type state and a hard state resulting from hard parton scattering. On the one hand, it allows one to quickly simulate relativistic heavy-ion collisions, and on the other hand, it reproduces and describes a number of experimental phenomena in the soft and hard sector. It also allows you to study many features of the interaction as interplay of soft and hard processes. Here we present some selected results of recent studies. Basically, new results on the correlation of elliptical flows at small and large transverse momenta at LHC energies are described. Current studies of the charge balance function at LHC energies and the A-dependence of the flow in heavy-ion collisions are also discussed. [ABSTRACT FROM AUTHOR]

Two microscopic models, UrQMD and QGSM, are used to extract the effective equation of state (EOS) of locally equilibrated nuclear matter produced in heavy-ion collisions at energies from 11.6 A GeV to 160 A GeV. Analysis is performed for the fixed central cubic cell of volume V = 125 fm3 and for the expanding cell that followed the growth of the central area with uniformly distributed energy. For all reactions the state of local equilibrium is nearly approached in both models after a certain relaxation period. The EOS has a simple linear dependence P = c2se with 0.12 [?] c2s [?] 0.145. Heavy resonances are shown to be responsible for deviations of the c2s(T) and c2s(mB) from linear behavior. In the T-mB and T-mS planes the EOS has also almost linear dependence and demonstrates kinks related not to the deconfinement phase transition but to inelastic freeze-out in the system. [ABSTRACT FROM AUTHOR]

We propose an entirely new method to study the phase diagram of strongly interacting matter by means of scattering the two colliding beams at the fixed target. Here we present the results of simulations of the most central triple nuclear collisions with the UrQMD 3.4 model for the beam center-of-mass collision energies s NN = 2.76 TeV and s NN = 200 GeV . The main outcome of our modeling is that even at these very high collision energies the initial baryonic charge densities are about 3 times higher than the ones achieved in the ordinary binary nuclear collisions. As a result, for instance, the yields of protons and Λ -hyperons are strongly enhanced in the triple nuclear collisions. The other prospective applications of this method are briefly discussed. Among them we consider the low energy collisions of three nuclei of lead, passing through an intermediate system with an electric charge of 246 units which exceeds essentially the critical value of 173 and, hence, this may be of crucial importance to study the spontaneous emission of positron-electron pairs from the vacuum. We present the convincing arguments that the triple nuclear collisions method will allow the high energy nuclear physics community to create a new frontier in the studies of the QCD phase diagram and to lift up these studies to an entirely new level. [ABSTRACT FROM AUTHOR]

Partial contributions of elliptic ν2 and triangular ν3 flows to the hexagonal ν6 flow are studied within the hydjet++ model for Pb+Pb collisions at sv = 2.76 TeV. Scaling of the ratio ν1/66{ψ2}/ν1/22{ψ2} in the elliptic flow plane, 2, is predicted in the range 1 ≤ pt ≤ 4 GeV/c for semicentral and semiperipheral collisions. Jets increase this ratio by about 10% and also cause its rise at pt ≥ 3.5 GeV/c. The part of ν6 coming from ν2 is instantly increasing as the reaction becomes more peripheral, whereas the contribution of ν3 to ν6 drops. This behavior explains the experimentally observed increase of correlations between second and sixth harmonics and the decrease of correlations between third and sixth harmonics with rising impact parameter b. Our study favors the idea that basic features of the hexagonal flow can be understood in terms of the interplay of elliptic and triangular flows. [ABSTRACT FROM AUTHOR]

Here, we develop an original approach to investigate the grand canonical partition function of the multicomponent mixtures of Boltzmann particles with hard-core interaction in finite and even small systems of the volumes above 20 fm3. The derived expressions of the induced surface tension equation of state (EoS) are analyzed in detail. It is shown that the metastable states, which can emerge in the finite systems with realistic interaction, appear at very high pressures at which the hadron resonance gas, most probably, is not applicable at all. It is shown how and under what conditions the obtained results for finite systems can be generalized to include into a formalism the equation for curvature tension. The applicability range of the obtained equations of induced surface and curvature tensions for finite systems is discussed and their close relations to the equations of the morphological thermodynamics are established. The hadron resonance gas model on the basis of the obtained advanced EoS is worked out. Also, this model is applied to analyze the chemical freeze-out of hadrons and light nuclei with the number of (anti-) baryons not exceeding 4. Their multiplicities were measured by the ALICE Collaboration in the central lead–lead collisions at the center-of-mass energy s NN = 2. 7 6 TeV. [ABSTRACT FROM AUTHOR]

A simple geometrical model with event-by-event fluctuations is suggested to study elliptical and triangular eccentricities in the initial state of relativistic heavy-ion collisions. This model describes rather well the ALICE and ATLAS data for Pb + Pb collisions at center-of-mass energy TeV per nucleon pair, assuming that the second, v2, and third, v3, harmonics of the anisotropic flow are simply linearly proportional to the eccentricities ɛ2 and ɛ3, respectively. We show that the eccentricity ɛ3 has a pure fluctuation origin and is substantially dependent on the size of the overlap area only, while the eccentricity ɛ2 is mainly related to the average collision geometry. Elliptic flow, therefore, is weakly dependent on the event-by-event fluctuations everywhere except of the very central collisions 0%–2%, whereas triangular flow is mostly determined by the fluctuations. The scaling dependence of the magnitude of the flow harmonics on atomic number, vn ∝ A−1/3, is predicted for this centrality interval. [ABSTRACT FROM AUTHOR]

The recently developed hadron resonance gas model with multicomponent hard-core repulsion is used to address and resolve the long standing problem to describe the light nuclear cluster multiplicities including the hyper-triton measured by the STAR Collaboration, known as the hyper-triton chemical freeze-out puzzle. An improved description for the hadronic and light nuclear cluster data measured by STAR at the collision energy s NN = 200 GeV and by ALICE at s NN = 2.76 TeV is obtained. This is achieved by applying a new strategy of analyzing the light nuclear cluster data and by using the value for the hard-core radius of the (anti-) Λ hyperons found in earlier work. One of the most striking results of the present work is that for the most probable scenario of chemical freeze-out for the STAR energy the obtained parameters allow to simultaneously reproduce the values of the experimental ratios S 3 and S ¯ 3 which were not included in the fit. [ABSTRACT FROM AUTHOR]

Here we develop a new strategy to analyze the chemical freeze-out of light (anti)nuclei produced in high energy collisions of heavy atomic nuclei within an advanced version of the hadron resonance gas model. It is based on two different, but complementary approaches to model the hard-core repulsion between the light nuclei and hadrons. The first approach is based on an approximate treatment of the equivalent hard-core radius of a roomy nuclear cluster and pions, while the second approach is rigorously derived here using a self-consistent treatment of classical excluded volumes of light (anti)nuclei and hadrons. By construction, in a hadronic medium dominated by pions, both approaches should give the same results. Employing this strategy to the analysis of hadronic and light (anti)nuclei multiplicities measured by ALICE at s NN = 2.76 TeV and by STAR at s NN = 200 GeV, we got rid of the existing ambiguity in the description of light (anti)nuclei data and determined the chemical freeze-out parameters of nuclei with high accuracy and confidence. At ALICE energy the nuclei are frozen prior to the hadrons at the temperature T = 175. 1 - 3.9 + 2.3 MeV, while at STAR energy there is a single freeze-out of hadrons and nuclei at the temperature T = 167.2 ± 3.9 MeV. We argue that the found chemical freeze-out volumes of nuclei can be considered as the volumes of quark-gluon bags that produce the nuclei at the moment of hadronization. [ABSTRACT FROM AUTHOR]

The hybrid model HYDJET++, which considers soft and hard processes, is employed for the analysis of dihadron angular correlations measured in Pb+Pb collisions at center-of-mass energy √sNN = 2.76 TeV. The model allows the study of both individual and mutual influence of lower flow harmonics, v2 and v3, on higher harmonics and dihadron angular correlations. It is shown that the typical structure called a ridge in dihadron angular correlations in a broad pseudorapidity range could appear just as the interplay of v2 and v3. Central, semi-central, and semi-peripheral collisions were investigated. Comparison of model results with the experimental data on dihadron angular correlations is presented for different centralities and transverse momenta pT. [ABSTRACT FROM AUTHOR]

Publisher Erratum: Eur. Phys. The original article can be found online at https://doi.org/10.1140/epja/s10050-022-00793-9. [Extracted from the article]

We propose a novel family of equations of state for symmetric nuclear matter based on the induced surface tension concept for the hard-core repulsion. It is shown that having only four adjustable parameters the suggested equations of state can, simultaneously, reproduce not only the main properties of the nuclear matter ground state, but the proton flow constraint up its maximal particle number densities. Varying the model parameters we carefully examine the range of values of incompressibility constant of normal nuclear matter and its critical temperature, which are consistent with the proton flow constraint. This analysis allows us to show that the physically most justified value of nuclear matter critical temperature is 15.5-18 MeV, the incompressibility constant is 270-315 MeV and the hard-core radius of nucleons is less than 0.4 fm. [ABSTRACT FROM AUTHOR]

Experiments with gold-gold collisions at the RHIC have revealed (i) stronger suppression of charmonium production at forward rapidity than at mid-rapidity and (ii) the similarity between the suppression degrees at RHIC and SPS energies. To describe these findings we employ the model that includes nuclear shadowing effects, calculated within the Glauber-Gribov theory, rapidity-dependent absorptive mechanism, caused by energy-momentum conservation, and dissociation and recombination of the charmonium due to interaction with co-moving matter. The free parameters of the model are tuned and fixed by comparison with experimental data at lower energies. A good agreement with the RHIC results concerning the rapidity and centrality distributions is obtained for both heavy Au+Au and light Cu+Cu colliding systems. For pA and A+A collisions at the LHC the model predicts stronger suppression of the charmonium and bottomonium yields in stark contrast to thermal model predictions. [ABSTRACT FROM AUTHOR]