arXiv subjects

A. A. Soldatov

Publications and source records attributed to A. A. Soldatov.

35 records · Page 2Linked to original sources

arXiv2018

Estimates of the baryon densities attainable in heavy-ion collisions from the beam energy scan program

The baryon and energy densities attained in fragmentation regions in central Au+Au collisions in the energy range of the Beam Energy Scan (BES) program at the Relativistic Heavy-Ion Collider (RHIC) are estimated within the model of the three-fluid dynamics. It is shown that a considerable part of the baryon charge is stopped in the central fireball. Even at 39 GeV, approximately 70% of the total baryon charge turns out to be stopped. The fraction of this stopped baryon charge decreases with collision energy rise, from 100% at 7.7 GeV to $\sim$40% at 62 GeV. The highest initial baryon densities of the thermalized matter, $n_B/n_0 \approx$ 10, are reached in the central region of colliding nuclei at $\sqrt{s_{NN}}=$ 20--40 GeV. These highest densities develop up to quite moderate freeze-out baryon densities at the midrapidity because the matter of the central fireball is pushed out to fragmentation regions by one-dimensional expansion. Therefore, consequences of these high initial baryon densities can be observed only in the fragmentation regions of colliding nuclei in AFTER@LHC experiments in the fixed-target mode.

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arXiv2018

Vortex rings in fragmentation regions in heavy-ion collisions at $\sqrt{s_{NN}}=$ 39 GeV

Vorticity generated in heavy-ion collisions at energy of $\sqrt{s_{NN}}=$ 39 GeV is studied. Simulations are performed within a model of the three-fluid dynamics. A peculiar structure consisting of two vortex rings is found: one ring in the target fragmentation region and another one in the projectile fragmentation region. These rings are also formed in central collisions. The matter rotation is opposite in this two rings. These vortex rings are already formed at the early stage of the collision together with primordial fragmentation regions. The average vorticity, responsible for the global polarization of the observed $Λ$ and $\barΛ$, is also studied. In the semi-central collisions the average vorticity in the midrapidity region turns out to be more than an order of magnitude lower than the total one. The total vorticity is dominated by the contributions of the fragmentation regions and is produced because of asymmetry of the vortex rings in noncentral collisions. This suggests that in semi-central collisions the global polarization in the fragmentation regions should be at least an order of magnitude higher than that observed by the STAR collaboration in the midrapidity. This polarization should be asymmetrical in the reaction plain and correlate with the corresponding directed flow.

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arXiv2018

Bulk Properties of the Matter Produced at Energies of the Beam Energy Scan Program

Recent STAR data on the bulk observables in the energy range of the Beam-Energy Scan Program at the Relativistic Heavy-Ion Collider are analyzed within the model of the three-fluid dynamics (3FD). The simulations are performed with different equations of state (EoS). The purely hadronic EoS fails to reproduce the data. A good, though imperfect, overall reproduction of the data is found within the deconfinement scenarios. The crossover EoS turns out to be slightly preferable. For this reproduction a fairly strong baryon stopping in the quark-gluon phase is required. The 3FD model does not need two separate freeze-outs (i.e. kinetic and chemical ones) to describe the STAR data. A unified freeze-out is applied at all energies.

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arXiv2018

High baryon and energy densities achievable in heavy-ion collisions at $\sqrt{s_{NN}}=$ 39 GeV

Baryon and energy densities, which are reached in central Au+Au collisions at collision energy of $\sqrt{s_{NN}}= 39$ GeV, are estimated within the model of three-fluid dynamics. It is shown that the initial thermalized mean proper baryon and energy densities in a sizable central region approximately are $n_B/n_0 \approx$ 10 and $\varepsilon\approx$ 40 GeV/fm$^3$, respectively. The study indicates that the deconfinement transition at the stage of interpenetration of colliding nuclei makes the system quite opaque. The final fragmentation regions in these collisions are formed not only by primordial fragmentation fireballs, i.e. the baryon-rich matter passed through the interaction region (containing approximately 30\% of the total baryon charge), but also by the baryon-rich regions of the central fireball pushed out to peripheral rapidities by the subsequent almost one-dimensional expansion of the central fireball along the beam direction.

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arXiv2017

Bose-Einstein condensation of magnons and spin superfluidity in the polar phase of $^3$He

The polar phase of $^3$He, which is topological spin-triplet superfluid with the Dirac nodal line in the spectrum of Bogolubov quasiparticles, has been recently stabilized in a nanoconfined geometry. We pump magnetic excitations (magnons) into the sample of polar phase and observe how they form a Bose-Einstein condensate, revealed by coherent precession of the magnetization of the sample. Spin superfluidity, which supports this coherence, is associated with the spontaneous breaking of U(1) symmetry by the phase of precession. We observe the corresponding Nambu-Goldstone boson and measure its mass emerging when applied rf field violates the U(1) symmetry explicitly. We suggest that the magnon BEC in the polar phase is a powerful probe for topological objects such as vortices and solitons and topological nodes in the fermionic spectrum.

cond-mat.other↗

arXiv2017

Light fragment production at CERN Super Proton Synchrotron

Recent data on the deutron and $^3$He production in central Pb+Pb collisions at the CERN Super Proton Synchrotron (SPS) energies measured by the NA49 collaboration are analyzed within the model of the three-fluid dynamics (3FD) complemented by the coalescence model for the light-fragment production. The simulations are performed with different equations of state---with and without deconfinement transition. It is found that scenarios with the deconfinement transition are preferable for reproduction rapidity distributions of deuterons and $^3$He, the corresponding results well agree with the experimental data. At the same time the calculated transverse-mass spectra of $^3$He at midrapidity do not that nice agree with the experimental data. The latter apparently indicates that coalescence coefficients should be temperature and/or momentum dependent.

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arXiv2017

Influence of Magnetic Scattering on Superfluidity of 3He in Nematic Aerogel

We report results of experiments with superfluid 3He confined in aerogels with parallel strands which lead to anisotropic scattering of 3He quasiparticles. We vary boundary conditions for the scattering by covering the strands by different numbers of atomic 4He layers and observe that the superfluid phase diagram and the nature of superfluid phases strongly depend on the coverage. We assume that the main reason of these phenomena is a magnetic channel of the scattering which becomes important at low coverages. Our results show that the magnetic channel also may be important in other Fermi systems with the triplet pairing.

cond-mat.supr-con↗

arXiv2017

Vorticity in heavy-ion collisions at the JINR Nuclotron-based Ion Collider fAcility

Vorticity of matter generated in noncentral heavy-ion collisions at energies of the Nuclotron-based Ion Collider fAcility (NICA) at the Joint Institute for Nuclear Research (JINR) in Dubna is studied. Simulations are performed within the model of the three-fluid dynamics (3FD) which reproduces the major part of bulk observables at these energies. Comparison with earlier calculations is done. Qualitative pattern of the vorticity evolution is analyzed. It is demonstrated that the vorticity is mainly located at the border between participants and spectators. In particular, this implies that the relative $Λ$-hyperon polarization should be stronger at rapidities of the fragmentation regions than that in the midrapidity region.

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arXiv2016

Entropy Production and Effective Viscosity in Heavy-Ion Collisions

Entropy production and an effective viscosity in central Au+Au collisions are estimated in a wide range of incident energies 3.3 GeV $\le \sqrt{s_{NN}}\le$ 39 GeV. The simulations are performed within a three-fluid model employing three different equations of state with and without deconfinement transition, which are equally good in reproduction of the momentum-integrated elliptic flow of charged particles in the considered energy range. It is found that more that 80\% entropy is prodused during a short early collision stage which lasts $\sim$1 fm/c at highest considered energies $\sqrt{s_{NN}}\ge$ 20 GeV. The estimated values of the viscosity-to-entropy ratio ($η/s$) are approximately the same in all considered scenarios. At final stages of the system expansion they range from $\sim$0.05 at highest considered energies to $\sim$0.5 lowest ones. It is found that the $η/s$ ratio decreases with the temperature ($T$) rise approximately as $\sim 1/T^4$ and exhibits a rather weak dependence on the net-baryon density.

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arXiv2016

Observation of half-quantum vortices in topological superfluid 3He

One of the most sought-after objects in topological quantum matter systems is a vortex carrying half a quantum of circulation. They were originally predicted to exist in superfluid 3He-A, but have never been resolved there. Here we report an observation of half-quantum vortices (HQVs) in the polar phase of superfluid 3He. The vortices are created with rotation or by the Kibble-Zurek mechanism and identified based on their nuclear magnetic resonance signature. This discovery provides a pathway for studies of unpaired Majorana modes bound to the HQV cores in the polar-distorted A phase.

cond-mat.other↗

arXiv2016

Interaction of two magnetic resonance modes in polar phase of superfluid 3He

We report results of low frequency nuclear magnetic resonance (NMR) experiments in the superfluid polar phase of 3He which is stabilized by a new type of "nematic" aerogel - nafen. We have found that an interaction between transverse and longitudinal NMR modes may essentially influence the spin dynamics. Theoretical formulas for NMR resonant frequencies are derived and applied for interpretation of the experimental results.

cond-mat.other↗

arXiv2016

Estimation of the Shear Viscosity from 3FD Simulations of Au+Au Collisions at $\sqrt{s_{NN}}=$ 3.3--39 GeV

An effective shear viscosity in central Au+Au collisions is estimated in the range of incident energies 3.3 GeV $\le \sqrt{s_{NN}}\le$ 39 GeV. The simulations are performed within a three-fluid model employing three different equations of state with and without the deconfinement transition. In order to estimate this effective viscosity, we consider the entropy produced in the 3FD simulations as if it is generated within the conventional one-fluid viscous hydrodynamics. It is found that the effective viscosity within different considered scenarios is very similar at the expansion stage of the collision: as a function of temperature ($T$) the viscosity-to-entropy ratio behaves as $η/s \sim 1/T^4$; as a function of net-baryon density ($n_B$), $η/s \sim 1/s$, i.e. it is mainly determined by the density dependence of the entropy density. The above dependencies take place along the dynamical trajectories of Au+Au collisions. At the final stages of the expansion the $η/s$ values are ranged from $\sim$0.05 at highest considered energies to $\sim$0.5 at the lowest ones.

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arXiv2016

What can we learn from the directed flow in heavy-ion collisions at BES RHIC energies?

Analysis of directed flow ($v_1$) of protons, antiprotons and pions in heavy-ion collisions is performed in the range of collision energies $\sqrt{s_{NN}}$ = 2.7--39 GeV. Simulations have been done within a three-fluid model employing a purely hadronic equation of state (EoS) and two versions of the EoS with deconfinement transitions: a first-order phase transition and a smooth crossover transition. The crossover EoS is unambiguously preferable for the description of the most part of experimental data in this energy range. The directed flow indicates that the crossover deconfinement transition takes place in semicentral Au+Au collisions in a wide range of collision energies 4 \lsim\sqrt{s_{NN}}\lsim$ 30 GeV. The obtained results suggest that the deconfinement EoS's in the quark-gluon sector should be stiffer at high baryon densities than those used in the calculation. The latter finding is in agreement with that discussed in astrophysics.

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arXiv2015

Polar phase of superfluid 3He in anisotropic aerogel

We report the observation of a new superfluid phase of 3He -- polar phase. This phase appears in 3He confined in a new type of aerogel with nearly parallel arrangement of strands which play a role of ordered impurities. Our observations qualitatively agree with theoretical predictions and suggest that in other systems with unconventional Cooper pairing (e.g. in unconventional superconductors) similar phenomena may be found in presence of anisotropic impurities.

cond-mat.supr-con↗

arXiv2015

Spin diffusion in liquid 3He confined in nafen

We report results of spin diffusion measurements in normal phase of liquid 3He confined in nafen. Nafen is a new type of aerogel and it consists of Al2O3 strands which are nearly parallel to one another at macroscopic distances. We examine two samples of nafen with different porosities using spin echo techniques. Spin diffusion of 3He along and across the strands was measured. The aerogel alignment is clearly evident from observed spin diffusion anisotropy. A theory describing this effect is developed and compared with the experiment.

cond-mat.supr-con↗

arXiv2015

Elliptic Flow in Heavy-Ion Collisions at Energies $\sqrt{s_{NN}}=$ 2.7--39 GeV

The transverse-momentum integrated elliptic flow of charged particles at midrapidity, $v_2$(charged), and that of identified hadrons from Au+Au collisions are computed in a wide range of incident energies 2.7 GeV $\le \sqrt{s_{NN}}\le$ 39 GeV. The simulations are performed within a three-fluid model employing three different equations of state (EoS's): a purely hadronic EoS and two versions of the EoS involving the deconfinement transition---a first-order phase transition and a smooth crossover one. The present simulations demonstrate low sensitivity of $v_2$(charged) to the EoS. All considered scenarios equally well reproduce recent STAR data on $v_2$(charged) for mid-central Au+Au collisions and properly describe its change of sign at the incident energy decrease below $\sqrt{s_{NN}}\approx$ 3.5 GeV. The predicted integrated elliptic flow of various species exhibits a stronger dependence on the EoS. A noticeable sensitivity to the EoS is found for anti-baryons and, to a lesser extent, for $K^-$ mesons. In particular, the $v_2$ excitation functions of anti-baryons exhibit a non-monotonicity within the deconfinement scenarios that was predicted by Kolb, Sollfrank and Heinz. However, low multiplicities of anti-baryons at $\sqrt{s_{NN}}\leq$ 10 GeV result in large fluctuations of their $v_2$ which may wash out this non-monotonicity.

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arXiv2015

Directed Flow Indicates a Crossover Deconfinement Transition in Relativistic Nuclear Collisions

Analysis of directed flow ($v_1$) of protons, antiprotons and pions in heavy-ion collisions is performed in the range of incident energies $\sqrt{s_{NN}}$ = 2.7--27 GeV. Simulations have been done within a three-fluid model employing a purely hadronic equation of state (EoS) and two versions of the EoS involving deconfinement transitions: a first-order phase transition and a smooth crossover transition. High sensitivity of the directed flow, especially the proton one, to the EoS is found. The crossover EoS is favored by the most part of considered experimental data. A strong wiggle in the excitation function of the proton $v_1$ slope at the midrapidity obtained with the first-order-phase-transition EoS and a smooth proton $v_1$ with positive midrapidity slope, within the hadronic EoS unambiguously disagree with the data. The pion and antiproton $v_1$ also definitely testify in favor of the crossover EoS. The results obtained with deconfinement EoS's apparently indicate that these EoS's in the quark-gluon sector should be stiffer at high baryon densities than those used in the calculation.

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