International Journal of Modern Physics E

The future gold beams with energies of up to 3.8AGeV from the Nuclotron at JINR in Dubna are well suited to study the equation of state of dense baryonic matter, and to explore the microscopic degrees-of-freedom emerging at neutron star densities. The relevant observables in heavy-ion collisions at these energies include yield and multidifferential distributions of (multi-) strange particles, collective flow of identified particles, fluctuation of conserved quantities and hypernuclei. In order to measure these observables in Au $+$ Au collisions with rates of up to 50kHz, the Baryonic Matter@Nuclotron setup will be upgraded with a highly granulated and fast hybrid tracking system, and a forward calorimeter for event plane determination. The physics program, the detector upgrades and physics performance studies will be presented.

In this paper, we present systematic measurements of azimuthal anisotropy for strange hadrons ($K_s^0$, $\varphi$ and $\mathrm{\Lambda }$) and multi-strange hadrons ($\mathrm{\Xi }$ and $\mathrm{\Omega }$) at mid-rapidity ($\left|y\right|<1.0$) in U$+$U collisions at $\sqrt{s_{NN}}=193$ GeV using the STAR detector at the Relativistic Heavy Ion Collider (RHIC). Flow coefficients ($v_2$, $v_3$ and $v_4$) are presented as a function of transverse momentum ($p_T$) for minimum bias and three different centrality intervals. The $\eta$ sub-event plane method is used to obtain the results. These measurements are compared with the published results from Au$+$Au collisions at $\sqrt{s_{NN}}=200$ GeV. Number of Constituent Quark (NCQ) scaling of the measured flow coefficients in U$+$U collisions is discussed. We also present the ratio of $v_n$ scaled by the participant eccentricity (${𝜀}_n\{2\}$) to explore system size dependence and collectivity in U$+$U collisions. The measured flow coefficients are compared with hydrodynamic and transport model calculations.

A radiopure cadmium tungstate scintillator enriched in ${}^{106}$Cd to 66% (${}^{106}$CdWO₄) operates in coincidence (anticoincidence) with two CdWO₄ scintillation counters to search for double-beta processes in ${}^{106}$Cd. After 26033 h of data taking, no effects were observed. The half-life limits on the different channels of ${}^{106}$Cd double-beta decay were set at the level of $T_{1/2}\sim 10^{20}-10^{22}$ yr. A new stage of the experiment is running with an improved sensitivity to all the decay channels thanks to reduction of the background and improvement of the energy resolution.

Here, we report on the results and prospects of the LHCb experiment at CERN as well as the upgrades of the LHCb detector within the scope of heavy-ion physics. A particular attention will be given to the extension of the fixed-target program and to the performance of the detector in high-occupancy nucleus–nucleus collisions. The technical description will be followed by a discussion of the results and the prospects for heavy-ion physics in fixed-target and collider mode.

In this paper, we put our focus towards describing the nonperturbative effects in the properties of hadrons made from the light-heavy and the heavy–heavy quarks in the framework of Instanton Liquid Model (ILM) of QCD vacuum. The main features of ILM and its applicability in the heavy quark sector are briefly discussed. The properties of gluonic systems, the light and heavy quark correlators in the instanton background are also analyzed. We demonstrate that the consideration of both, perturbative and nonperturbative, gluon effects in the instanton background for a single heavy quark leads to the mass shift due to the direct-instanton nonperturbative and ILM modified perturbative contributions, respectively. For the interacting heavy quark and heavy anti-quark, the potential consists of the direct instanton-induced part and the one-gluon exchange (OGE) perturbative part. OGE interactions are screened at large distances due to the nonperturbative dynamics. The estimation of instanton contributions in the phenomenological Cornell-type potential model is presented. In relation to the experimental data, the charmonium properties, the role of instanton effects in their spectra and transitions are discussed. The main features of heavy-light quark systems in the instanton generated background are also discussed. As an example, we consider the process of pion emissions by the exited heavy quarkonium. We show that there is a sizable correction ($\sim 20\%$) to the dipole approximation for the process $\psi (2S)\to J/\psi {\pi }^{+}{\pi }^{-}$.

In this paper, we analyzed charged particle transverse momentum spectra in high multiplicity events in proton–proton and nucleus–nucleus collisions at LHC energies from the ALICE experiment using the color string percolation model (CSPM). The color reduction factor and associated string density parameters are extracted for various multiplicity classes in $pp$ collisions and centrality classes for heavy-ion collisions at various LHC energies to study the effect of collision geometry and collision energy. These parameters are used to extract the thermodynamical quantities temperature and the energy density of the hot nuclear matter. A universal scaling is observed in initial temperature when studied as a function of charged particle multiplicity scaled by transverse overlap area. From the measured initial energy density $𝜀$ and the initial temperature T, a dimensionless quantity $𝜀/T^4$ is constructed which is used to obtain the degrees of freedom (DOF) of the deconfined phase. A two-step behavior and a sudden increase in DOF of $\sim$47 for the ideal gas, above the hadronization temperature (T $\approx$ 210MeV), are observed in case of heavy-ion collisions at LHC energies.

The scarce knowledge of the initial stages of quark-gluon plasma before the thermalization is mostly inferred through the low-$p_{\perp }$ sector. We propose a complementary approach in this report — the use of high-$p_{\perp }$ probes’ energy loss. We study the effects of four commonly assumed initial stages, whose temperature profiles differ only before the thermalization, on high-$p_{\perp }$$R_{\mathrm{\text{AA}}}$ and $v_2$ predictions. The predictions are based on our Dynamical Radiative and Elastic ENergy-loss Approach (DREENA) framework. We report insensitivity of $v_2$ to the initial stages, making it unable to distinguish between different cases. $R_{\mathrm{\text{AA}}}$ displays sensitivity to the presumed initial stages, but current experimental precision does not allow resolution between these cases. We further revise the commonly accepted procedure of fitting the energy loss parameters, for each individual initial stage, to the measured $R_{\mathrm{\text{AA}}}$. We show that the sensitivity of $v_2$ to various initial stages obtained through such procedure is mostly a consequence of fitting procedure, which may obscure the physical interpretations. Overall, the simultaneous study of high-$p_{\perp }$ observables, with unchanged energy loss parametrization and restrained temperature profiles, is crucial for future constraints on initial stages.