Time evolution of shear viscosity η, entropy density s, and their ratio η/s in the central area of central gold-gold collisions at NICA energy range is studied within the UrQMD transport model. The extracted values of energy density, net baryon density and net strangeness density are used as input to (i) statistical model of ideal hadron gas to define temperature, baryo-chemical potential and strangeness chemical potential, and to (ii) UrQMD box with periodic boundary conditions to study the relaxation process of highly excited matter. During the relaxation stage, the shear viscosity is determined in the framework of Green-Kubo approach. The procedure is performed for each of 20 time slices, corresponding to conditions in the central area of the fireball at times from 1 fm/c to 20 fm/c. For all tested energies the ratio η/s reaches minimum, (η/s) min ≈ 0.3 at t ≈ 5 fm/c. Then it increases up to the late stages of the system evolution. This rise is accompanied by the drop of both, temperature and strangeness chemical potential, and increase of baryo-chemical potential.

The production of $$K^{0}_{S}$$ K S 0 mesons in inelastic p+p collisions at beam momentum 158 $$\text{ GeV }/c$$ GeV / c ($$\sqrt{s_{NN}}=17.3$$ s NN = 17.3  $$\text{ GeV }$$ GeV ) was measured with the NA61/SHINE spectrometer at the CERN Super Proton Synchrotron. Double-differential distributions were obtained in transverse momentum and rapidity. The mean multiplicity of $$K^{0}_{S}$$ K S 0 was determined to be $$0.162 \pm 0.001 (stat.) \pm 0.011 (sys.)$$ 0.162 ± 0.001 ( s t a t . ) ± 0.011 ( s y s . ) . The results on $$K^{0}_{S}$$ K S 0 production are compared with model predictions (EPOS 1.99, SMASH 2.0, PHSD and UrQMD 3.4 models) as well as with published world data.

NA61/SHINE is an experiment at the CERN Super Proton Synchrotron. The main goals of the experiment are the search for the critical point of strongly interacting matter and the study of the properties of the onset of deconfinement. To reach these goals, the two-dimensional scan in beam momentum (13A − 150A GeV/c) and system size (p+p, Be+Be, Ar+Sc, Xe+La, Pb+Pb) was performed. In the final stage of the collision, the spectra of protons are only weakly affected by the effects of resonance decays and rescattering due to their large mass. Thus, proton rapidity distribution is particularly sensitive to the onset of deconfinement. This article presents experimental results on proton production in the collision energy range, which is most relevant to the onset of deconfinement. The procedure of measuring the proton rapidity spectra by NA61/SHINE is described, as well as Collaboration’s recent results from reactions of p+p, Be+Be and Ar+Sc. Presented experimental results are confronted with existing data and models.

The production of backward nucleons, N (180 • ), at 180 • in the nuclear target rest frame in protonnucleus (p + A) collisions is studied. The backward nucleons appearing outside of the kinematically allowed range of proton-nucleon (p + N ) reactions are shown to be due to secondary reactions of heavy baryonic resonances produced inside the nucleus. Baryonic resonances R created in primary p + N reactions can change their masses and momenta due to successive collisions R + N → R + N with other nuclear nucleons. Two distinct mechanisms and kinematic restrictions are studied: the reaction R + N → N (180 • ) + N and the resonance decay R → N (180 • ) + π. Simulations of p + A collisions using the Ultra-relativistic Quantum Molecular Dynamics model support these mechanisms and are consistent with available data on proton backward production.

Measurements of $$K^{*}(892)^0$$ K ∗ ( 892 ) 0 resonance production via its $$K^{+}\pi ^{-}$$ K + π - decay mode in inelastic p+p collisions at beam momenta 40 and 80 $$\text{ GeV }\!/\!c$$ GeV / c ($$\sqrt{s_{NN}}=8.8$$ s NN = 8.8 and 12.3 $$\text{ GeV }$$ GeV ) are presented. The data were recorded by the NA61/SHINE hadron spectrometer at the CERN Super Proton Synchrotron. The template method was used to extract the $$K^{*}(892)^0$$ K ∗ ( 892 ) 0 signal. Transverse momentum and rapidity spectra were obtained. The mean multiplicities of $$K^{*}(892)^0$$ K ∗ ( 892 ) 0 mesons were found to be $$(35.1 \pm 1.3 \mathrm {(stat)} \pm 3.6 \mathrm {(sys))} \cdot 10^{-3}$$ ( 35.1 ± 1.3 ( stat ) ± 3.6 ( sys ) ) · 10 - 3 at 40 $$\text{ GeV }\!/\!c$$ GeV / c and $$(58.3 \pm 1.9 \mathrm {(stat)} \pm 4.9 \mathrm {(sys))} \cdot 10^{-3}$$ ( 58.3 ± 1.9 ( stat ) ± 4.9 ( sys ) ) · 10 - 3 at 80 $$\text{ GeV }\!/\!c$$ GeV / c . The NA61/SHINE results are compared with the Epos1.99 and Hadron Resonance Gas models as well as with world data. The transverse mass spectra of $$K^{*}(892)^0$$ K ∗ ( 892 ) 0 mesons and other particles previously reported by NA61/SHINE were fitted within the Blast-Wave model. The transverse flow velocities are close to 0.1–0.2 of the speed of light and are significantly smaller than the ones determined in heavy nucleus-nucleus interactions at the same beam momenta.