Search Results (22)

For a new parameterization of the modified effective chiral model, developed primarily to regulate the density content of the symmetry energy and its higher order terms, equations of state (EoSs) for hyperon-rich matter (H) and delta baryon matter ($\Delta$) were obtained. The models were used to investigate the emission of gravitational waves (GWs) through f-mode oscillations in the corresponding neutron stars. We obtained the stellar structure, f-mode frequency and tidal deformability $\mathsf{\Lambda }$ for our models. We report that the $\Delta$ EoS is stiffer compared to the H EoS. We also analyzed the velocity of sound in these media. The corresponding mass–radius relationships were obtained and compared with various observations. We studied the dependence of f-mode frequencies on the stellar mass, redshift and tidal deformability. We employed the well known Cowling approximation to obtain the f-mode frequencies for $l=2,3$ and 4 modes of oscillation. We found that the f-mode frequencies of the H and $\Delta$ EoSs were almost the same in the lower mass region, while we observed a substantial difference between them in the high-mass region. We also obtained an empirical relation for the EoSs considered. The various attributes obtained for our models showed close agreement with various observational constraints from pulsars and GW events. Full article

The strange baryon production in Bi + Bi collisions at $\sqrt{s_{NN}}=9.0$ GeV is studied using the PHSD transport model. Hyperon and anti-hyperon yields, transverse momentum spectra, and rapidity spectra are calculated, and their centrality dependence and the effect of rapidity and transverse momentum cuts are studied. The rapidity distributions for $\overline{\mathsf{\Lambda }}$, $\mathsf{\Xi }$, $\overline{\mathsf{\Xi }}$ baryons are found to be systematically narrower than for $\mathsf{\Lambda }$s. The $p_T$ slope parameters for anti-hyperons vary more with centrality than those for hyperons. Restricting the accepted rapidity range to $\left|y\right|<1$ increases the slope parameters by 13–30 MeV, depending on the centrality class and the hyperon mass. Hydrodynamic velocity and vorticity fields are calculated, and the formation of two oppositely rotating vortex rings moving in opposite directions along the collision axis is found. The hyperon spin polarization induced by the medium vorticity within the thermodynamic approach is calculated, and the dependence of the polarization on the transverse momentum and rapidity cuts and on the centrality selection is analyzed. The cuts have stronger effect on the polarization of $\mathsf{\Lambda }$ and $\mathsf{\Xi }$ hyperons than on the corresponding anti-hyperons. The polarization signal is maximal for the centrality class, 60–70%. We show that, for the considered hyperon polarization mechanism, the structure of the vorticity field makes an imprint on the polarization signal as a function of the azimuthal angle in the transverse momentum plane, ${\varphi }_H$, $cos{\varphi }_H=p_x/p_T$. For particles with positive longitudinal momentum, $p_z>0$, the polarization increases with $cos{\varphi }_H$, while for particles with $p_z<0$ it decreases. Full article

We investigate the $\cos 2{\varphi }_h$ azimuthal asymmetry contributed by the coupling of the Boer–Mulders function and the Collins function in $K^{\pm }$- and $\mathsf{\Lambda }$-hyperon-produced SIDIS process. The asymmetry is studied under the transverse-momentum-dependent (TMD) factorization framework at the leading order by considering the TMD evolution effects that utilize the parametrization for non-perturbative Sudakov form factors. The DGLAP evolution effects of the collinear counterpart of the Collins function of the final-state hadrons are considered by introducing the approximated evolution kernels. We utilize the available parametrization for the proton Boer–Mulders function and the Collins function of $K^{\pm }$. For the Collins function of the $\mathsf{\Lambda }$ hyperon, the result of the diquark spectator model is adopted due to the absence of parametrization. The numerical results of the $\cos 2{\varphi }_h$ azimuthal asymmetry are obtained in the kinematic regions of EIC and EicC. It can be shown that the asymmetry is much smaller than the Sivers asymmetry, which means that the convolution of the Boer–Mulders function and the Collins function may not be the main contributor to the $\cos 2{\varphi }_h$ asymmetry. We emphasize the importance of future measurement of the $\cos 2{\varphi }_h$ asymmetry to unravel different contributors. Full article

We present a systematic study of the global polarization of $\Lambda$ and $\overline{\Lambda }$ hyperons in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=19.6$ GeV using the viscous hydrodynamic model CCNU-LBNL-Viscous hydrodynamic model (CLVisc) with a modified 3D optical Glauber model initial condition. The global polarization splitting as a function of transverse momentum and rapidity is investigated. It is shown that the magnitude of the net baryon density and its longitudinal titled geometry at the initial stage both have significant effects on the global polarization splitting of $\Lambda$ and $\overline{\Lambda }$ hyperons. Specifically, an increase in the magnitude of the net baryon density leads to a corresponding minor increase in the global polarization splitting. Similarly, alterations in the tilted geometry of net baryon density results in significant changes in the splitting of the global polarization. Full article

The matter of neutron stars is characterised by the density of the order of typical nuclear densities; hence, it can be described with methods of nuclear physics. However, at high densities, some effects that are absent in nuclear and hypernuclear physics can appear, and this makes neutron stars a good place for studying the properties of baryonic interactions. In the present work, we consider neutron stars consisting of nucleons, leptons and $\mathrm{\Lambda }$ hyperons with Skyrme baryonic forces. We study the character of the $\mathrm{\Lambda }N$ interactions taking place in neutron stars at high densities. In particular, we show the difference between three-body $\mathrm{\Lambda }NN$ and density-dependent $\mathrm{\Lambda }N$ forces. We also demonstrate that the Skyrme $\mathrm{\Lambda }N$ forces proportional to nuclear density are better suited for the modelling of neutron stars than the forces proportional to fractional powers of density. Finally, we emphasize the importance of the point of appearance of hyperons in a further search for parameterizations which are suitable for describing neutron stars. Full article

Fast and efficient algorithms optimized for high performance computers are crucial for the real-time analysis of data in heavy-ion physics experiments. Furthermore, the application of neural networks and other machine learning techniques has become more popular in physics experiments over the last years. For that reason, a fast neural network package called ANN4FLES is developed in C++, which will be optimized to be used on a high performance computer farm for the future Compressed Baryonic Matter (CBM) experiment at the Facility for Antiproton and Ion Research (FAIR, Darmstadt, Germany). This paper describes the first application of ANN4FLES used in the reconstruction chain of the CBM experiment to replace the existing particle competition between $K_s$-mesons and $\mathrm{\Lambda }$-hyperons in the KF Particle Finder by a neural network based approach. The raw classification performance of the neural network reaches over 98% on the testing set. Furthermore, it is shown that the background noise was reduced by the neural network-based competition and therefore improved the quality of the physics analysis. Full article

The MicroBooNE detector is a liquid argon time projection chamber (LArTPC) with an 85 ton active mass that receives flux from the Booster Neutrino and the Nutrinos from the Main Injector (NuMI) beams, providing excellent spatial resolution of the reconstructed final-state particles. Since 2015, MicroBooNE has accumulated many neutrino and anti-neutrino scattering events with argon nuclei enabling searches for rare interaction channels. The Cabibbo-suppressed production of hyperons in anti-neutrino–nucleus interactions provides sensitivity to a range of effects, including second-class currents, SU(3) symmetry violations and reinteractions between the hyperon and the nuclear remnant. This channel exclusively involves anti-neutrinos, offering an unambiguous constraint on wrong-sign contamination. The effects of nucleon structure and final state interactions are distinct from those affecting the quasielastic channel and modify the $\Lambda$ and $\Sigma$ production cross sections in different ways, providing new information that could help to break their degeneracy. Few measurements of this channel have been made, primarily in older experiments such as Gargamelle. We present the sensitivity of the MicroBooNE experiment to the cross section for direct (Cabibbo-suppressed) $\Lambda$ production in muon anti-neutrino interactions, using anti-neutrinos from the off-axis NuMI beam. Full article

We investigate Collins asymmetry in the $\mathrm{\Lambda }$ hyperon produced semi-inclusive deep inelastic scattering (SIDIS) process based on the kinematical region of Electron-ion collider in China (EicC) and Electron–ion collider (EIC) within the transverse momentum dependence (TMD) factorization framework at next-to-leading-logarithmic order. The asymmetry is contributed by the convolution of the target proton transversity distribution function and the Collins function of the final-state $\mathrm{\Lambda }$ hyperon. The TMD evolution effect of the corresponding parton distribution functions (PDFs) and fragmentation functions (FFs) is considered with the help of parametrization of the non-perturbative Sudakov form factors for the proton PDFs and $\mathrm{\Lambda }$ fragmentation functions. We apply the parametrization of the collinear proton transversity distribution function and the model results of $\mathrm{\Lambda }$ Collins function from the diquark spectator model as the inputs of the TMD evolution to numerically calculate Collins asymmetry in $\mathrm{\Lambda }$ produced SIDIS process at the kinematical configurations of EIC and EicC. It can be shown that the asymmetry is significant and can be measured at EIC and EicC. The flavor dependence of transversity distribution functions could be further constrained by studying the $\mathrm{\Lambda }$ hyperon produced SIDIS process in the future to improve our understanding of the spin structure within nucleons. Full article

Due to its sensitivity to the dynamics of strongly interacting matter subject to extreme conditions, hyperon global polarization has become an important observable to study the system created in relativistic heavy-ion collisions. Recently, the STAR and HADES collaborations have measured the global polarization of both $\mathrm{\Lambda }$ and $\overline{\mathrm{\Lambda }}$ produced in semi-central collisions in a wide range of collision energies. The polarization excitation functions show an increasing trend as the collision energy decreases, with the increase being more pronounced for the $\overline{\mathrm{\Lambda }}$. In this work, we make a summary of a core-corona model that we have developed to quantify the global polarization contributions from $\mathrm{\Lambda }$ and $\overline{\mathrm{\Lambda }}$ created in different regions of the fireball. The core-corona model assumes that $\mathrm{\Lambda }$s and $\overline{\mathrm{\Lambda }}$s are produced in both regions, the high-density core and the lower density corona, with different relative abundances which modulate the polarization excitation function. We have shown that the model works well for the description of experimental results. The global polarization excitation functions computed with the model show a peak at different collision energies in the region $\sqrt{s_{NN}}\le 10$ GeV. Finally, we discuss and report on the model global polarization predictions for BES-II, NICA and CBM at FAIR and HADES energies. Full article

The gold–gold collisions at $\sqrt{s_{NN}}=7.7$ and 11.5 GeV are simulated within the PHSD transport model. In each collision event, the spectator nucleons are separated and the fluidization procedure for the participants is performed. The local velocities are determined in the Landau frame and the kinematic and thermal vorticity fields are evaluated. We analyze the thermodynamic properties of the cells where Λs and $\overline{\Lambda }$s were born or had their last interaction. Such cells contribute to the formation of the observed global polarization of hyperons induced by the thermal vorticity of the medium. The $\overline{\Lambda }$ polarization signal is found to be mainly determined by hot, dense, and highly vortical cells at the earlier stage of the collision, whereas the Λ polarization signal is accumulated over the longer time and includes cells with lower vorticity. The calculated global polarizations for both Λs and $\overline{\Lambda }$s agree well with the experimental finding by the STAR collaboration at energy $\sqrt{s_{NN}}=11.5 \mathrm{G}\mathrm{e}\mathrm{V}.$ For collisions at $\sqrt{s_{NN}}=7.7 \mathrm{G}\mathrm{e}\mathrm{V},$ we can reproduce the STAR data for Λ hyperons, but significantly underpredict the observed global polarization of $\overline{\Lambda }$. Furthermore, we consider the centrality dependence of the hyperon polarization in collisions at 7.7 GeV. It increases with an increase of centrality, reaches a maximum at 65–75% and then starts decreasing rapidly for peripheral collisions. Full article

We review recent studies of vortical motion and the resulting polarization of $\mathsf{\Lambda }$ hyperons in heavy-ion collisions at NICA energies, in particular, within the model of three-fluid dynamics (3FD). This includes predictions of the global $\mathsf{\Lambda }$ polarization and ring structures that appear in Au+Au collisions. The global $\mathsf{\Lambda }$ polarization in Au+Au collisions is calculated, including its rapidity and centrality dependence. The contributions of the thermal vorticity and meson-field term (proposed by Csernai, Kapusta, and Welle) to the global polarization are considered. The results are compared with data from recent STAR and HADES experiments. It is predicted that the polarization maximum is reached at $\sqrt{s_{NN}}\approx$ 3 GeV if the measurements are performed with the same acceptance. It is demonstrated that a pair of vortex rings are formed, one at forward rapidities and another at backward rapidities, in ultra-central Au+Au collisions at $\sqrt{s_{NN}}>$ 4 GeV. The vortex rings carry information about the early stage of the collision, in particular, the stopping of baryons. It is shown that these rings can be detected by measuring the ring observable $R_{\mathsf{\Lambda }}$, even in the midrapidity region at $\sqrt{s_{NN}}=$ 5–20 GeV. At forward/backward rapidities, the $R_{\mathsf{\Lambda }}$ signal is expected to be stronger. The possibility of observing the vortex-ring signal against the background of non-collective transverse polarization is discussed. Full article

JLab has recently found indications of the possible existence of a $\Sigma NN$ resonance at $(3.14\pm 0.84)-i(2.28\pm 1.2)$ MeV. In the past, using models that exploit symmetries between the two-baryon sector with and without strangeness, hyperon–nucleon interactions that reproduce the experimental data of the strangeness $-1$ sector have been derived. We make use of these interactions to review the existing Faddeev studies of the $\Lambda NN-\Sigma NN$ system that show theoretical evidence of a $(I,J^P)=(1,1/2^{+})$$\Sigma NN$ quasibound state near the threshold. The calculated position of the pole is at 2.92$-i$2.17 MeV, which is in reasonable agreement with the experimental findings. Full article

Here, we propose a novel approach to experimentally and theoretically study the properties of QCD matter under new extreme conditions, namely having an initial temperature over 300 MeV and baryonic charge density over three times the values of the normal nuclear density. According to contemporary theoretical knowledge, such conditions were not accessible during the early Universe evolution and are not accessible now in the known astrophysical phenomena. To achieve these new extreme conditions, we proposed performing high-luminosity experiments at LHC or other colliders by means of scattering the two colliding beams at the nuclei of a solid target that is fixed at their interaction region. Under plausible assumptions, we estimate the reaction rate for the p+C+p and Pb+Pb+Pb reactions and discuss the energy deposition into the target and possible types of fixed targets for such reactions. To simulate the triple nuclear collisions, we employed the well-known UrQMD 3.4 model for the beam center-of-mass collision energies $\sqrt{s_{NN}}$ = 2.76 TeV. As a result of our modeling, we found that, in the most central and simultaneous triple nuclear collisions, the initial baryonic charge density is approximately three times higher than the one achieved in the ordinary binary nuclear collisions at this energy. Full article

To study binary neutron star systems and to interpret observational data such as gravitational-wave and kilonova signals, one needs an accurate description of the processes that take place during the final stages of the coalescence, for example, through numerical-relativity simulations. In this work, we present an updated version of the numerical-relativity code BAM in order to incorporate nuclear-theory-based equations of state and a simple description of neutrino interactions through a neutrino leakage scheme. Different test simulations, for stars undergoing a neutrino-induced gravitational collapse and for binary neutron stars systems, validate our new implementation. For the binary neutron stars systems, we show that we can evolve stably and accurately distinct microphysical models employing the different equations of state: SFHo, DD2, and the hyperonic BHB$\Lambda \varphi$. Overall, our test simulations have good agreement with those reported in the literature. Full article

Exclusive hyperon-antihyperon production provides a unique insight for understanding of the intrinsic dynamics when strangeness is involved. In this paper, we review the results of $\Lambda \overline{\Lambda }$ production via different reactions from various experiments, e.g., via $\overline{p}p$ annihilation from the LEAR experiment PS185, via electron-positron annihilation using the energy scan method at the CLEO-c and BESIII experiments and the initial-state-radiation approach utilized at the BaBar experiment. The production cross section of $\Lambda \overline{\Lambda }$ near the threshold is sensitive to QCD based prediction. Experimental high precision data for $\overline{p}p\to \overline{\Lambda }\Lambda$ close to the threshold region is obtained. The cross section of $e^{+}{e}^{-}\to \Lambda \overline{\Lambda }$ is measured from its production threshold to high energy. A non-zero cross section for $e^{+}{e}^{-}\to \Lambda \overline{\Lambda }$ near threshold is observed at BaBar and BESIII, which is in disagreement with the pQCD prediction. However, more precise data is needed to confirm this observation. Future experiments, utilizing $\overline{p}p$ reaction such as PANDA experiment or electron-positron annihilation such as the BESIII and BelleII experiments, are needed to extend the experimental data and to understand the $\Lambda \overline{\Lambda }$ production. Full article