Hyperon Nucleon Research Articles

Theoretical study on [formula omitted] and [formula omitted] correlation functions

We examine the Λ-4He (α) and Ξα momentum correlation in high-energy collisions to further elucidate the properties of the hyperon–nucleon interactions. For the Λα system, we compare Λα potential models with different strengths at short range. We find that the difference among the models is visible in the momentum correlation from a small-size source. This indicates that the Λα momentum correlation can constrain the property of the ΛN interaction at short range, which plays an essential role in dense nuclear matter. For the Ξα system, we employ the folding Ξα potential based on the lattice QCD ΞN interactions. The Ξα potential supports a Coulomb assisted bound state of Ξ5H in the Ξ−α channel, while the Ξ0α channel is unbound. To examine the sensitivity of the correlation function to the nature of the Ξα potential, we vary the potential strength simulating stronger and weaker interactions. The result of the correlation function clearly reflects the bound state nature in the Ξ−α correlation.

Hypernuclei as a laboratory to test hyperon–nucleon interactions

Hypernuclei as a laboratory to test hyperon–nucleon interactions

Hyperon–nucleon interaction in chiral effective field theory at next-to-next-to-leading order

A hyperon–nucleon potential for the strangeness S=-1 sector (varLambda N, varSigma N) up to third order in the chiral expansion is presented. SU(3) flavor symmetry is imposed for constructing the interaction, however, the explicit SU(3) symmetry breaking by the physical masses of the pseudoscalar mesons and in the leading-order contact terms is taken into account. A novel regularization scheme is employed which has already been successfully used in studies of the nucleon–nucleon interaction within chiral effective field theory up to high orders. An excellent description of the low-energy varLambda p, varSigma ^- p and varSigma ^+ p scattering data is achieved. New data from J-PARC on angular distributions for the varSigma N channels are analyzed. Results for the hypertriton and A=4 hyper-nuclear separation energies are presented. An uncertainty estimate for the chiral expansion is performed for selected hyperon–nucleon observables.

Collective Excitation in High-Energy Nuclear Collisions—In Memory of Professor Lianshou Liu

We celebrate the legacies of our friend and mentor Professor Lianshou Liu who was one of the pioneers for the phenomenology of multi-particle interactions and initiated the physics of relativistic heavy-ion collisions in China. In this article, we discuss some of the recent exciting experimental observations on the collective phenomena including collectivity, chirality, criticality, strangeness production, and thermal equilibrium in high-energy nuclear collisions. Future directions, especially the physics at high baryon density, will be discussed with a focus on the first-order phase boundary and hyperon–nucleon interactions.

Astrophysical Implications on Hyperon Couplings and Hyperon Star Properties with Relativistic Equations of States

Hyperons are essential constituents in the neutron star interior. The poorly known hyperonic interaction is a source of uncertainty for studying laboratory hypernuclei and neutron star observations. In this work, we perform Bayesian inference of phenomenological hyperon–nucleon interactions using the tidal deformability measurement of the GW170817 binary neutron star merger as detected by LIGO/Virgo and the mass–radius measurements of PSR J0030+0541 and PSR J0740+6620 as detected by NICER. The analysis is based on a set of stiff relativistic neutron star matter equation of states with hyperons from the relativistic mean-field theory, naturally fulfilling the causality requirement and empirical nuclear matter properties. We specifically utilize the strong correlation recently deduced between the scalar and vector meson–hyperon couplings, imposed by the measured Λ separation energy in single-Λ hypernuclei, and perform four different tests with or without the strong correlation. We find that the laboratory hypernuclear constraint ensures a large enough Λ–scalar–meson coupling to match the large vector coupling in hyperon star matter. When adopting the current most probable intervals of hyperon couplings from the joint analysis of laboratory and astrophysical data, we find the maximum mass of hyperon stars is at most (68% credible interval) from the chosen set of stiff equation of states. The reduction of the stellar radius due to hyperons is quantified based on our analysis and various hyperon star properties are provided.

(I, JP) = (1, 1/2+)ΣNN Quasibound State

JLab has recently found indications of the possible existence of a ΣNN resonance at (3.14±0.84)−i(2.28±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 ΛNN−ΣNN system that show theoretical evidence of a (I,JP)=(1,1/2+)ΣNN quasibound state near the threshold. The calculated position of the pole is at 2.92−i2.17 MeV, which is in reasonable agreement with the experimental findings.

Recent results on hyperon pair production and nucleon time-like form factors at BESIII

The BESIII experiment, based on the BEPCII collider at IHEP in Beijing, China, is capable of measuring nucleon form factors with unprecedented precision. We report recent results achieved by the BESIII collaboration concerning the nucleon time-like form factors and the hyperon pair production. Specifically, we outline the results obtained by the study of the process e^+e^- \to p \overline pe+e−→pp¯, using both the scan-energy and initial-state radiation techniques, those of the process e^+e^- \to n \overline ne+e−→nn¯, and the study of the \SigmaΣ polarization regarding the process e^+e^- \to J/\psi \to \Sigma^+\overline \Sigma{}^-e+e−→J/ψ→Σ+Σ¯−.

Recent progress and future prospects of hyperon nucleon scattering experiment

A new hyperon-proton scattering experiment, dubbed J-PARC E40, was performed to measure differential cross sections of the Σ+p, Σ−p elastic scatterings and the Σ−p → Λn scattering by identifying a lot of Σ particles in the momentum ranging from 0.4 to 0.8 GeV/c produced by the π±p → K+Σ± reactions. We successfully measured the differential cross sections of these three channels with a drastically improved accuracy with a fine angular step. These new data will become important experimental constraints to improve the theories of the two-body baryon-baryon interactions. Following this success, we proposed a new experiment to measure the differential cross sections and spin observables by using a highly polarized Λ beam for providing quantitative information on the ΛN interaction. The results of three Σp channels and future prospects of the Λp scattering experiment are described.

Study of the Strong Interaction Among Hadrons with Correlations at the LHC

The strong interaction among hadrons has been measured in the past by scattering experiments. Although this technique has been extremely successful in providing information about the nucleon–nucleon and pion–nucleon interactions, when unstable hadrons are considered the experiments become more challenging. In the last few years, the analysis of correlations in the momentum space for pairs of stable and unstable hadrons measured in pp and p+Pb collisions by the ALICE Collaboration at the LHC has provided a new method to investigate the strong interaction among hadrons. In this article, we review the numerous results recently achieved for hyperon–nucleon, hyperon–hyperon, and kaon–nucleon pairs, which show that this new method opens the possibility of measuring the residual strong interaction of any hadron pair.

Systematic Nuclear Uncertainties in the Hypertriton System

The hypertriton bound state is relevant for inference of knowledge about the hyperon–nucleon (YN) interaction. In this work we compute the binding energy of the hypertriton using the ab initio hypernuclear no-core shell model (NCSM) with realistic interactions derived from chiral effective field theory. In particular, we employ a large family of nucleon–nucleon interactions with the aim to quantify the theoretical precision of predicted hypernuclear observables arising from nuclear-physics uncertainties. The three-body calculations are performed in a relative Jacobi-coordinate harmonic oscillator basis and we implement infrared correction formulas to extrapolate the NCSM results to infinite model space. We find that the spread of the predicted hypertriton binding energy, attributed to the nuclear-interaction model uncertainty, is about 100 keV. In conclusion, the sensitivity of the hypertriton binding energy to nuclear-physics uncertainties is of the same order of magnitude as experimental uncertainties such that this bound-state observable can be used in the calibration procedure to constrain the YN interactions.

Hyperon–nucleon three-body forces and strangeness in neutron stars

Three-body forces acting on a $\Lambda$ hyperon in a nuclear medium are investigated, with special focus on the so-called hyperon puzzle in neutron stars. The hyperon-nucleon two-body interaction deduced from SU(3) chiral effective field theory is employed at next-to-leading order. Hyperon-nucleon three-body forces are approximated using saturation by decuplet baryons and are transcribed to density-dependent effective two-body interactions. These together are taken as input in a Brueckner-Bethe-Goldstone equation with explicit treatment of the $\Lambda N\leftrightarrow\Sigma N$ and $\Lambda NN\leftrightarrow\Sigma NN$ coupled channels. Single-particle potentials of a $\Lambda$ hyperon in symmetric nuclear matter and neutron matter are calculated. With parameters of the $\Lambda NN$ three-body force constrained by hypernuclear phenomenology, extrapolations to high baryon density are performed. By comparison of the $\Lambda$ and neutron chemical potentials at densities characteristic of the core of neutron stars it is found that the combined repulsive effects of two- and three-body correlations makes the appearance of $\Lambda$ hyperons in neutron stars energetically unfavourable, thus offering a possible solution to a longstanding question.

Structure of single-$$\varLambda $$ hypernuclei with chiral hyperon–nucleon potentials

The structure of single-$\Lambda$ hypernuclei is studied using the chiral hyperon-nucleon potentials derived at leading order (LO) and next-to-leading order (NLO) by the J\"{u}lich--Bonn--Munich group. Results for the separation energies of $\Lambda$ single-particle states for various hypernuclei from $^5_{\Lambda}$He to $^{209}_{\,\,\,\,\,\Lambda}$Pb are presented for the LO interaction and the 2013 (NLO13) and 2019 (NLO19) versions of the NLO potentials. It is found that the results based on the LO potential show a clear tendency for overbinding while those for the NLO13 interaction underbind most of the considered hypernuclei. A qualitatively good agreement with the data is obtained for the NLO19 interaction over a fairly large range of mass number values when considering the uncertainty due to the regulator dependence. A small spin-orbit splitting of the $p$-, $d$-, $f$-, and $g$-wave states is predicted by all interactions, in line with the rather small values observed in pertinent experiments.

P-shell hypernuclear energy spectra using the Gogny-interaction shell model

Recent high-resolution experiments at JLab give the energy spectra of the hypernuclei , , and . However, their spins and parities of the excited states have not been known experimentally. In the present paper, we make a systematical theoretical investigation for the p-shell hypernuclei, within the shell model based on the nucleon–nucleon (NN) and hyperon–nucleon interactions. The effective NN interaction takes the finite-range density-dependent Gogny force, and the hyperon–nucleon interaction takes an empirical ΛN interaction which includes the ΛN–ΣN and ΣN–ΣN coupling effects. The shell model with the Gogny force without parameters being refitted can reasonably describe both spectra and binding energies of the p-shell nuclei, which gives a confidence for the further calculations of hypernuclei. We compare our results with experimental data as well as various theoretical calculations, and explain the recent experimental hypernuclear spectra observed at JLab.

Analytical solution for magnetic moments of Λ-hypernuclei in a relativistic approach

The magnetic moments of [Formula: see text]-hypernuclei are the most interesting observables which provide a highly sensitive probe of lambda in the hypernuclei structure and also supply direct information on hyperon–nucleon interactions. In this work, in a relativistic approach we analytically determine the magnetic moment of several [Formula: see text]-hypernuclei such as [Formula: see text], [Formula: see text] and [Formula: see text] in their ground and excited states, i.e., the [Formula: see text], [Formula: see text] and [Formula: see text] states. For our analysis, we consider the central potential of Wood–Saxon and the spin-orbital potential and determine the wave function of hypernuclei. Then, we compute the Dirac, the anomalous and the total magnetic moments of the ground and excited states of [Formula: see text]-hypernuclei.

Large-Nc operator analysis of hyperon–nucleon interactions in SU(3) chiral effective field theory

We study octet–octet baryon (JP=12+) contact interactions in SU(3) chiral effective field theory by using large-Nc operator analysis. By applying the 1/Nc expansion of the Hartree Hamiltonian, we find 15 operators in the octet–octet baryon potential where 4 operators for the leading order (LO) and 11 for the next-to-next-to-leading order (NNLO). The large-Nc operator analysis of octet–octet baryon matrix elements reduces the number of free parameters from 15 to 6 at the LO of the 1/Nc expansion. The application of large-Nc sum rules to the Jülich model of hyperon–nucleon (YN) interactions at the LO of the chiral expansion reduces the model parameters to 3 from 5 at the LO of 1/Nc expansion. We find that the values of LECs fitted to YN scattering data in Ref. [21] in the relativistic covariant ChEFT (EG) approach are more consistent with the predictions of the large-Nc analysis than in the heavy baryon (HB) formalism approach.

Meson–baryon coupling constants of the SU(3) baryons with flavor SU(3) symmetry breaking

We investigate the strong coupling constants for the baryon octet–octet, decuplet–octet, and decuplet–decuplet vertices with pseudoscalar mesons within a general framework of the chiral quark-soliton model, taking into account the effects of flavor SU(3) symmetry breaking to linear order in the expansion of the strange current quark mass. All relevant dynamical parameters are fixed by using the experimental data on hyperon semileptonic decays and the singlet axial-vector constant of the nucleon. The results of the strong coupling constants for the baryon octet and the pseudoscalar meson octet are compared with those determined from the Jülich–Bonn potential and the Nijmegen extended soft-core potential for hyperon–nucleon scattering. The results of the strong decay widths of the baryon decuplet are in good agreement with the experimental data. The effects of SUf(3) symmetry breaking are sizable on the η′ coupling constants. We predict also the strong coupling constants for the Ω baryons.

Giant Monopole Resonance and Nuclear Incompressibility of Hypernuclei**Supported by the National Natural Science Foundation of China under Grant Nos 11575060, 11775014, 11505058 and 11435014.

The isoscalar giant monopole resonances (ISGMRs) of hypernuclei , , and are investigated using a fully self-consistent Skyrme–Hartree–Fock plus random phase approximation method. The Skyrme-type forces, SGII, No.5 and SΛΛ1, are adopted to describe the nucleon–nucleon, Λ hyperon–nucleon and Λ hyperon–Λ hyperon (ΛΛ) interactions, respectively. For a given hyperon fraction, we find that effects of ΛΛ interaction on the properties of infinite symmetric nuclear matter and finite hypernuclei are very small. The ISGMR strengths are shifted to the high energy region when two Λ are added into normal nuclei. The changes are from two parts, one is due to the mean field calculations, and the other is from the residual interaction associated with Λ hyperons. The constrained energies are increased by about 0.5–0.7 MeV, which consequently enhances the effective incompressibility modulus of hypernuclei.

Light neutron-rich hypernuclei from the importance-truncated no-core shell model

We explore the systematics of ground-state and excitation energies in singly-strange hypernuclei throughout the helium and lithium isotopic chains — from HeΛ5 to HeΛ11 and from LiΛ7 to LiΛ12 — in the ab initio no-core shell model with importance truncation. All calculations are based on two- and three-baryon interaction from chiral effective field theory and we employ a similarity renormalization group transformation consistently up to the three-baryon level to improve the model-space convergence. While the absolute energies of hypernuclear states show a systematic variation with the regulator cutoff of the hyperon–nucleon interaction, the resulting neutron separation energies are very stable and in good agreement with available data for both nucleonic parents and their daughter hypernuclei. We provide predictions for the neutron separation energies and the spectra of neutron-rich hypernuclei that have not yet been observed experimentally. Furthermore, we find that the neutron drip lines in the helium and lithium isotopic chains are not changed by the addition of a hyperon.

Electric dipole moment of the deuteron in the standard model with NN − ΛN − ΣN coupling

We calculate the electric dipole moment (EDM) of the deuteron in the standard model with |ΔS|=1 interactions by taking into account the NN−ΛN−ΣN channel coupling, which is an important nuclear level systematics. The two-body problem is solved with the Gaussian Expansion Method using the realistic Argonne v18 nuclear force and the YN potential which can reproduce the binding energies of Λ3H, Λ3He, and Λ4He. The |ΔS|=1 interbaryon potential is modeled by the one-meson exchange process. It is found that the deuteron EDM is modified by less than 10%, and the main contribution to this deviation is due to the polarization of the hyperon–nucleon channels. The effect of the YN interaction is small, and treating ΛN and ΣN channels as free is a good approximation for the EDM of the deuteron.

Study of the Few Nucleon Systems at CLAS

The study of few nucleon systems with electromagnetic probes is an essential component of the scientific program carried out at the Thomas Jefferson National Accelerator Facility (JLab). Here we present measurements of exclusive reactions on light nuclei using real photon beams with energies up to 3 GeV and the CEBAF Large Acceptance Spectrometer (CLAS), a nearly 4pi magnetic spectrometer, in order to study the properties of strongly interacting matter and the transition from hadronic (i.e in terms of nucleons and mesons) to partonic (in terms of quark and gluons) degrees of freedom in nuclear interactions. We discuss the progress made in understanding the relevant degrees of freedom using polarisation observables and cross sections of deuteron and ^3He photodisintegration in the few-GeV photon-energy region. In addition, recent high-statistics experiments with the CLAS detector have provided us with sufficient counting rates to study the effects of initial- and final-state interactions in reactions off the deuteron. Such data allow us to extract a large set of polarisation observables for final-state interactions in hyperon photoproduction and to study the properties of the hyperon–nucleon interaction. Initial-state effects are studied by mapping the dependence of experimental observables on the spectator-nucleon momentum. We also present recent results for polarisation observables for quasi-free K^+varLambda off the bound proton in a deuteron as well as for final-state interactions in the reaction gamma drightarrow K^+varLambda n, and will discuss their impact on hyperon–nucleon studies.