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I demonstrate how the thermal abundances of S = −1 strange baryons can be computed based on the density of states extracted from a coupled-channel model.

The production of Ξ(1321)- and Ξ¯(1321)+ hyperons in inelastic p+p interactions is studied in a fixed target experiment at a beam momentum of 158 Ge/c. Double differential distributions in rapidity y and transverse momentum pT are obtained from a sample of 33M inelastic events. They allow to extrapolate the spectra to full phase space and to determine the mean multiplicity of both Ξ- and Ξ¯+. The rapidity and transverse momentum spectra are compared to transport model predictions. The Ξ- mean multiplicity in inelastic p+p interactions at 158 Ge/c is used to quantify the strangeness enhancement in A+A collisions at the same centre-of-mass energy per nucleon pair.

The electroproduction of hypernuclei initiates a captivating domain of study, offering great insights into the characteristics of composite nucleon-hyperon systems. This inquiry assumes prime significance as it displays critical features of nuclear matter structure and tests the interactions between hyperons and nucleons. In this paper, we unveil the distorted-wave impulse approximation (DWIA) approach, aimed at explaining the cross sections in electroproduc-tion of Λ-hypernuclei. Our investigation examines how various model assumptions affect the results we get. We focus on two important factors: influence of the proton Fermi motion and description of the various models of nuclear and hypernuclear structure.

We study the global polarizations of Λ, Ξ − , and Ω − hyperons in noncentral Au + Au collisions at √ S NN = 7.7-200 GeV. We highlight the importance of effect of decay feeddown to the measured global polarization. With the decay contributions taken into account, the global polarization ordering P Ω− > P Ξ− > P Λ can be naturally explained, which is consistent with the observation recently reported from the STAR experiment from Au+Au collisions at 200 GeV. We also extend our calculations to predict expectations from the RHIC-BES II data.

The global polarization of Λ hyperons has been measured in Au+Au and Ag+Ag collisions at √ S NN = 2.4 and 2.55 GeV recorded with HADES. An increase of the polarization is observed following the trend measured by the STAR Collaboration. The high statistics Ag+Ag data allowed for differential measurements of the polarization. The study of acceptance effects is very important in the fixed target setup, as the phase-space coverage is not symmetric. These studies are reported together with the evaluation procedure of the systematic uncertainties.

In this work, we conduct an extensive study of the conditions that allow the mass-gap object in the GW190814 event to be faced as a degenerate star instead of a black hole. We begin by revisiting some parameterizations of quantum hadrodynamics and then study under which conditions hyperons are present in such a massive star. Afterward, using a vector MIT-based model, we study whether self-bound quark stars, satisfying the Bodmer–Witten conjecture, fulfill all the observational constraints. Finally, we study hybrid stars within a Maxwell construction and check for what values of the bag, as well as the vector interaction, a quark core star with only nucleons, and with nucleons admixed with hyperons can reach at least 2.50 M ⊙. We conclude that, depending on the choice of parameters, none of the possibilities can be completely ruled out, i.e., the mass-gap object can be a hadronic (either nucleonic or hyperonic), a quark, or a hybrid star, although some cases are more probable than others.

The measurement of an alignment between the angular momentum of a non-central collision between heavy ions and the spin of emitted particles reveals that the fluid produced in the collision is extremely vortical. Colliding ions go into a vortex When heavy ions such as gold collide in a particle collider, they form exotic states of matter that are similar to fluids. If the particles hit non-centrally, then the fluid is predicted to have vortices. However, these vortices have not yet been observed in an experiment. Here, the STAR Collaboration shows that during gold–gold collisions, spin alignment of Λ hyperons with the angular momentum of the fluid occurs. This is experimental evidence of the formation of vortices. They also show that the fluid produced in heavy-ion collisions has the highest vorticity ever observed. The results could provide general insights into how vortices form in ideal liquids. The extreme energy densities generated by ultra-relativistic collisions between heavy atomic nuclei produce a state of matter that behaves surprisingly like a fluid, with exceptionally high temperature and low viscosity 1 . Non-central collisions have angular momenta of the order of 1,000 ћ , and the resulting fluid may have a strong vortical structure 2 , 3 , 4 that must be understood to describe the fluid properly. The vortical structure is also of particular interest because the restoration of fundamental symmetries of quantum chromodynamics is expected to produce novel physical effects in the presence of strong vorticity 5 . However, no experimental indications of fluid vorticity in heavy ion collisions have yet been found. Since vorticity represents a local rotational structure of the fluid, spin–orbit coupling can lead to preferential orientation of particle spins along the direction of rotation. Here we present measurements of an alignment between the global angular momentum of a non-central collision and the spin of emitted particles (in this case the collision occurs between gold nuclei and produces Λ baryons), revealing that the fluid produced in heavy ion collisions is the most vortical system so far observed. (At high energies, this fluid is a quark–gluon plasma.) We find that Λ and hyperons show a positive polarization of the order of a few per cent, consistent with some hydrodynamic predictions 6 . (A hyperon is a particle composed of three quarks, at least one of which is a strange quark; the remainder are up and down quarks, found in protons and neutrons.) A previous measurement 7 that reported a null result, that is, zero polarization, at higher collision energies is seen to be consistent with the trend of our observations, though with larger statistical uncertainties. These data provide experimental access to the vortical structure of the nearly ideal liquid 8 created in a heavy ion collision and should prove valuable in the development of hydrodynamic models that quantitatively connect observations to the theory of the strong force.

We review the role and properties of hyperons in finite and infinite nuclear systems. In particular, we present different production mechanisms of hypernuclei, as well as several aspects of hypernuclear γ-ray spectroscopy, and the weak decay modes of hypernuclei. Then we discuss the construction of hyperon–nucleon and hyperon–hyperon interactions on the basis of the meson-exchange and chiral effective field theories. Recent developments based on the so-called Vlow k approach and lattice quantum chromodynamics will also be addressed. Finally, we go over some of the effects of hyperons on the properties of neutron and proto-neutron stars with an emphasis on the so-called ‘hyperon puzzle’, i.e. the problem of the strong softening of the equation of state, and the consequent reduction of the maximum mass, induced by the presence of hyperons, a problem which has become more intriguing and difficult to solve due the recent measurements of approximately 2M⊙ millisecond pulsars. We discuss some of the solutions proposed to tackle this problem. We also re-examine the role of hyperons on the cooling properties of newly born neutron stars and on the development of the so-called r-mode instability.

The equation of state (EOS) of neutron matter plays a decisive role in understanding the neutron star properties and the gravitational waves from neutron star mergers. At sufficient densities, the appearance of hyperons generally softens the EOS, leading to a reduction in the maximum mass of neutron stars well below the observed values of about 2 M⊙. Even though repulsive three-body forces are known to solve this so-called “hyperon puzzle,” so far performing ab initio calculations with a substantial number of hyperons for neutron star properties has remained elusive. Starting from the newly developed auxiliary field quantum Monte Carlo algorithm to simulate hyperneutron matter without any sign oscillations, we derive three distinct EOSs by employing the state-of-the-art nuclear lattice effective field theory. We include NΛ, ΛΛ two-body forces, NNΛ, and NΛΛ three-body forces. Consequently, we determine essential astrophysical quantities such as the neutron star mass, radius, tidal deformability, and universal I–Love–Q relation. The maximum mass, radius, and tidal deformability of a 1.4 M⊙ neutron star are predicted to be 2.17(1)(1) M⊙, R1.4M⊙ = 13.10(1)(7) km, and Λ1.4M⊙=597(5)(18) , respectively, based on our most realistic EOS. These predictions are in good agreement with the latest astrophysical constraints derived from observations of massive neutron stars, gravitational waves, and joint mass–radius measurements. In addition, for the first time in ab initio calculations, we investigate both nonrotating and rotating neutron star configurations. The results indicate that the impact of rotational dynamics on the maximum mass is small, regardless of whether hyperons are present in the EOS or not.

One of the key challenges for nuclear physics today is to understand from first principles the effective interaction between hadrons with different quark content. First successes have been achieved using techniques that solve the dynamics of quarks and gluons on discrete space-time lattices 1 , 2 . Experimentally, the dynamics of the strong interaction have been studied by scattering hadrons off each other. Such scattering experiments are difficult or impossible for unstable hadrons 3 – 6 and so high-quality measurements exist only for hadrons containing up and down quarks 7 . Here we demonstrate that measuring correlations in the momentum space between hadron pairs 8 – 12 produced in ultrarelativistic proton–proton collisions at the CERN Large Hadron Collider (LHC) provides a precise method with which to obtain the missing information on the interaction dynamics between any pair of unstable hadrons. Specifically, we discuss the case of the interaction of baryons containing strange quarks (hyperons). We demonstrate how, using precision measurements of proton–omega baryon correlations, the effect of the strong interaction for this hadron–hadron pair can be studied with precision similar to, and compared with, predictions from lattice calculations 13 , 14 . The large number of hyperons identified in proton–proton collisions at the LHC, together with accurate modelling 15 of the small (approximately one femtometre) inter-particle distance and exact predictions for the correlation functions, enables a detailed determination of the short-range part of the nucleon-hyperon interaction. Correlations in momentum space between hadrons created by ultrarelativistic proton–proton collisions at the CERN Large Hadron Collider provide insights into the strong interaction, particularly the short-range dynamics of hyperons—baryons that contain strange quarks.