Production and Interactions of Hyperons and Hypernuclei

Nature Reviews Physics, 2021

A hypernucleus, a sub-atomic bound system with at least one hyperon, is a great test ground to investigate nuclear forces and general baryonic interactions with up, down and strange quarks. Hypernuclei have been extensively studied for almost seven decades in reactions involving cosmic-rays and with accelerator beams. In recent years, experimental studies of hypernuclei have entered a new stage using energetic collisions of heavy-ion beams. However, these investigations have revealed two puzzling results related to the lightest three-body hypernuclear system, the so-called hypertriton and the unexpected existence of a bound state of two neutrons with a Λ hyperon. Solving these puzzles will not only impact our understanding of the fundamental baryonic interactions with strange quarks, but also of the nature of the deep interior of neutron stars. In this Perspective, we discuss approaches to solving these puzzles including experiments with heavy-ion beams and the analysis of nuclear emulsions using state-of-the-art technologies. We summarise ongoing projects and experiments at various facilities worldwide and outline future perspectives.

Nuclear Physics A

Formation of hypernuclei in peripheral collisions of relativistic light and heavy ions is studied theoretically within the transport and statistical approaches. New mechanisms for the formation of strange nuclear systems via capture of hyperons by slightly excited spectator matter and their subsequent disintegration are investigated. These processes lead to production of specific and exotic hypernuclei, which may not be accessible in other reactions. Similar mechanisms processing via absorption of strange particles by nuclei can take place in reactions initiated by electrons, antiprotons and other hadrons. It is demonstrated that our approach is consistent with experimental data.

Physical Review Letters, 2012

The low-energy nΣ − interactions determine, in part, the role of the strange quark in dense matter, such as that found in astrophysical environments. The scattering phase shifts for this system are obtained from a numerical evaluation of the QCD path integral using the technique of lattice QCD. Our calculations, performed at a pion mass of mπ ∼ 389 MeV in two large lattice volumes, and at one lattice spacing, are extrapolated to the physical pion mass using effective field theory. The interactions determined from QCD are consistent with those extracted from hyperon-nucleon experimental data within uncertainties, and strengthen theoretical arguments that the strange quark is a crucial component of dense nuclear matter.

arXiv preprint arXiv:1101.3181, 2011

Stored antiproton beams at the international FAIR facility will provide unique opportunities to study hyperons as well as antihyperons in nuclear systems. Precise γ-spectroscopy of multistrange hypernuclei will serve as a laboratory for the hyperon-hyperon interaction. Exclusive hadron-antihadron pair production close to threshold can measure the potential of a antihadron relative to that of the coincident hadrons. In the present work we explore the production of excited states in double hypernuclei following the micro-canonical break-up of an initially excited double hypernucleus which is created by the absorption and conversion of a stopped Ξ − hyperon. Generally the formation of excited hypernuclear states relative to ground states dominates in this model. For different initial target nuclei which absorb the Ξ − , different double hypernuclei nuclei dominate. We also compare the model predictions with the correlated pion spectra measured by the E906 collaboration. In antiproton nucleus reactions the event-by-event transverse momentum correlations of hadronantihadron pairs produced close to threshold contain information on the difference between the nuclear potential of the hadron and the associated antihadron. For produced D-meson pairs at 6.7 GeV/c the sensitivity of the transverse momenta correlation will probably be to small to deduce differences between the potentials for D + and D − mesons. However, for ΞΞ pairs produced at 2.9 GeV/c the asymmetry is sufficiently sensitive to predicted differences between the Ξ and Ξ potentials even if the momentum and density dependence of the the potential are taken into account.

Exclusive A(p,K^+){_\Lambda}B and A(\pi,K^+){_\Lambda}B^\prime reactions leading to two body final states, have been investigated in a fully covariant model based on an effective Lagrangian picture. The explicit kaon production vertex is described via creation, propagation and decay into relevant channel of N*(1650), N*(1710) and N*(1720) intermediate baryonic resonance states, in the initial collision of the projectile with one of the target nucleons. The bound state wave functions are obtained by solving the Dirac equation with appropriate scalar and vector potentials. The calculated cross sections show strong sensitivity to the final hypernuclear state excited in the reaction. Cross sections of 1 - 2 nb/sr are obtained at peak positions of favored transitions in case of the A(p,K^+){_\Lambda}B reaction on heavier targets.

1993

We present a first calculation of the potential and spin-orbit coupling for hypernuclei in the framework of a nuclear-potential model based on a spontaneous collective (superradiant) pion-nucleon-delta interaction. A perturbative evaluation of the propagation of a hyperon in such a coherent medium leads to an effective hypernuclear potential of the same shape and roughly half the depth (i.e. ~ 30 MeV) of the standard nuclear potential and a negligible spin-orbit coupling for both h and Z hypernuclei. Such results are in complete agreement with existing experimental data. Moreover, in this framework, we are able to explain the surprisingly narrow decay widths of the Z hypernuclei.

The European Physical Journal A

The production of light (anti-)nuclei and (anti-)hypernuclei in ultra-relativistic heavy-ion collisions, but also in more elementary collisions as proton–proton and proton–nucleus collisions, became recently a focus of interest. In particular, the fact that these objects are all loosely bound compared to the temperature and energies, e.g. the kinetic energies involved, is often stressed out to be special for their production. The binding energies of these (anti-)nuclei is between 130 keV ($${\mathrm {\Lambda }}$$Λseparation energy in the hypertriton) and about 8 MeV per nucleon. Whereas the connected temperatures are of the order of 100 to 160 MeV. This lead to some difficulties in the interpretation of the usually discussed production models, i.e. coalescence and statistical-thermal models, as will be discussed here. In this brief review we discuss selected highlights of the production of light (anti-)nuclei, such as (anti-)deuteron, (anti-)helium and (anti-)alpha nuclei. In additi...

Brueckner theory is used to investigate the properties of hyperons in nuclear matter. The hyperon-nucleon interaction is taken from chiral effective field theory at next-to-leading order with SU(3) symmetric low-energy constants. Furthermore, the underlying nucleon-nucleon interaction is also derived within chiral effective field theory. We present the single-particle potentials of Λ and Σ hyperons in symmetric and asymmetric nuclear matter computed with the continuous choice for intermediate spectra. The results are in good agreement with the empirical information. In particular, our calculation gives a repulsive Σ-nuclear potential and a weak Λ-nuclear spin-orbit force.

Proceedings of the 12th International Conference on Hypernuclear and Strange Particle Physics (HYP2015), 2017

We develop a versatile model of hypernuclei production in relativistic hadron and ion collisions. Within a hybrid approach we use transport, coalescence and statistical models to describe the whole process. We demonstrate that heavy hypernuclei are coming mostly from projectile and target residues, whereas light hypernuclei can be produced at all rapidities. The yields of hypernuclei increase considerably above the energy threshold for the hyperon production, and there is a tendency to saturation of yields of hypernuclei with increasing the beam energy. There are unique opportunities in relativistic ion collisions which are difficult to realize in traditional hypernuclear experiments: The produced hypernuclei have a broad distribution in masses and isospin, and the production of multi-strange nuclei including new excited states is quite abundant. In addition, we can directly get an information on the hypermatter both at high and low temperatures.

A concise overview of fundamental Σ hypernuclei physics and the mechanisms of hypernucleus formation and interactions are presented. Σ−Λ interaction and strong force-mediated hyperon-nucleon interaction are introduced to give an epigrammatic background and current perspective of the subject. A model phenomenological elementary Sigma-Nucleus (Σ-N) potential has been constructed and reported here as an instance of ΣΝ interaction. The potential incorporates both spin and isospin dependence and may be useful in calculating Hamiltonians, cross sections and decay widths in Σ hypernuclear reactions. Keywords: ΣN potential; Σ−Λ conversion; woods-saxon potential; lane potential PACS numbers: 21.80.+a, 24.50.+g; 25.80.Nv