Hypernuclear Data Research Articles

Hypernuclear constraints on the existence and lifetime of a deeply bound H dibaryon

We study to what extent the unique observation of ΛΛ hypernuclei by their weak decay into known Λ hypernuclei, with lifetimes of order 10−10 s, rules out the existence of a deeply bound doubly-strange (S = − 2) H dibaryon. Treating ΛΛ6He (the Nagara emulsion event) in a realistic Λ−Λ−4He three-body model, we find that the HeΛΛ6→H+4He strong-interaction lifetime increases beyond 10−10 s for mH<mΛ+mn, about 176 MeV below the ΛΛ threshold, so that such a deeply bound H is not in conflict with hypernuclear data. Constrained by Λ hypernuclear ΔS=1 nonmesonic weak-interaction decay rates, we follow EFT methods to evaluate the ΔS=2H→nn weak-decay lifetime of H in the mass range 2mn≲mH<mΛ+mn. The resulting H lifetime is of order 105 s, many orders of magnitude shorter than required to qualify for a dark-matter candidate.

Effects of many-body interactions in hypernuclei with Korea-IBS-Daegu-SKKU functionals

We investigate the properties of $$\Lambda $$ hyperon in $$\Lambda $$ -hypernuclei using an effective nuclear density functional theory which is based on the low-energy effective field theory. It expands the energy density in the power of Fermi momentum, and consequently has multiple density dependence for the effective many-body interactions. Starting from the effective density functional for nucleons, we determine the parameters for the two- and many-body $$\Lambda $$ -N interactions added to the nucleon energy density functional by fitting to $$\Lambda $$ -hypernuclear data. The experimental data consist of the energy levels of a $$\Lambda $$ hyperon in the p-, and d-states as well as s-state of $$\Lambda $$ -hypernuclei in the mass range from $${}_\Lambda ^{16}\hbox {O}$$ to $${}_\Lambda ^{208}\hbox {Pb}$$ . The results turn out to properly explain the data relevant to hypernuclei owing to the effective many-body interaction apart from a few data in light hypernuclei. This hyperon functional is applied to study the $$\Lambda $$ hyperon binding energy of the neutron-rich $$^{124-136}_{\Lambda } \hbox {Sn}$$ isotopes which are under consideration for the measurement at J-PARC. Our results are shown to be insensitive to the density dependence of symmetry energy. We also examine the nuclear matter including $$\Lambda $$ hyperon. We note that the hyperon threshold density depends on the nuclear matter properties.

Systematic treatment of hypernuclear data and application to the hypertriton

A database is under construction to provide a complete collection of published basic properties of hypernuclei such as Λ binding energies, lifetimes, or excitation energies. From these values, averages with related errors are computed in a systematic way. For each property, the overall experimental situation is depicted in form of an ideogram showing the combined probability density function of the measurements. The database is accessible via a dynamic website at https://hypernuclei.kph.uni-mainz.de with an user interface offering customizable visualizations, selections, or unit conversions. The capabilities of the database are demonstrated for the puzzling and disputed data situation of the hypertriton.

Constraints on the varLambda -Neutron Interaction from Charge Symmetry Breaking in the mathbf {^4_Lambda mathrm{He}} - mathbf {^4_Lambda mathrm{H}} Hypernuclei

We utilize the experimentally known difference of the varLambda separation energies of the mirror hypernuclei {^4_varLambda mathrm{He}} and {^4_varLambda mathrm{H}} to constrain the varLambda -neutron interaction. We include the leading charge-symmetry breaking (CSB) interaction into our hyperon-nucleon interaction derived within chiral effective field theory at next-to-leading order. In particular, we determine the strength of the two arising CSB contact terms by a fit to the differences of the separation energies of these hypernuclei in the 0^+ and 1^+ states, respectively. By construction, the resulting interaction describes all low energy hyperon-nucleon scattering data, the hypertriton and the CSB in {^4_varLambda mathrm{He}}-{^4_varLambda mathrm{H}} accurately. This allows us to provide first predictions for the varLambda n scattering lengths, based solely on available hypernuclear data.

Thermal evolution of relativistic hyperonic compact stars with calibrated equations of state

A set of unified relativistic mean-field equations of state for hyperonic compact stars recently built in [M. Fortin, Ad. R. Raduta, S. Avancini, and C. Providencia, Phys. Rev. D {\bf 101}, 034017 (2020)] is used to study the thermal evolution of non-magnetized and non-rotating spherically-symmetric isolated and accreting neutron stars under different hypothesis concerning proton $S$-wave superfluidity. These equations of state have been obtained in the following way: the slope of the symmetry energy is in agreement with experimental data; the coupling constants of $\Lambda$ and $\Xi$-hyperons are determined from experimental hypernuclear data; uncertainties in the nucleon-$\Sigma$ interaction potential are accounted for; current constraints on the lower bound of the maximum neutron star mass are satisfied. Within the considered set of equations of state, the presence of hyperons is essential for the description of the cooling/heating curves. One of the conclusions we reach is that the criterion of best agreement with observational data leads to different equations of states and proton $S$-wave superfluidity gaps when applied separately for isolated neutron stars and accreting neutron stars in quiescence. This means that at least in one situation the traditional simulation framework that we employ is not complete and/or the equations of state are inappropriate. Another result is that, considering equations of state which do not allow for nucleonic dUrca or allow for it only in very massive NS, the low luminosity of SAX J1808 requires a repulsive $\Sigma$-hyperon potential in symmetric nuclear matter in the range $U_\Sigma^{(N)}\approx 10-30$ MeV. This range of values for $U_\Sigma^{(N)} $ is also supported by the criterion of best agreement with all available data from INS and XRT.

The continuum spectrum of hypernuclear trios

The spectrum of hypernuclear trios composed of a Λ baryon and two nucleons is the subject of an ongoing experimental campaign, aiming to study the interaction of the Λ particle with a neutron, and the 3-body Λ-nucleon-nucleon force. In this manuscript we utilize baryonic effective field theory at leading order, constrained to reproduce the available low energy light hypernuclear data, to study the continuum spectrum of such hypernuclear trios. Using the complex scaling method and the inverse analytic continuation in the coupling constant method we find the existence of a virtual state in the ΛnpJπ=3/2+ channel, leading to cross-section enhancement near threshold. For the ΛnnJπ=1/2+ channel we predict a resonance state. Depending, however, on the value of the ΛN scattering length, the resonance pole moves from the physical to the unphysical complex energy sheet within the experimental bounds.

Cooling of hypernuclear compact stars: Hartree–Fock models and high-density pairing

ABSTRACT The thermal evolution of hypernuclear compact stars is studied for stellar models constructed on the basis of covariant density functional theory in Hartree and Hartree–Fock approximation. Parametrizations of both types are consistent with the astrophysical mass constraints on compact stars and available hypernuclear data. We discuss the differences of these density functionals and highlight the effects they have on the composition and on the cooling of hypernuclear stars. It is shown that hypernuclear stars computed with density functional models that have a low symmetry energy slope, L, are fairly consistent with the cooling data of observed compact stars. The class of stellar models based on larger L values gives rise to the direct Urca process at low densities, which leads to significantly faster cooling. We conjecture high-density pairing for protons and Λ’s in the P-wave channel and provide simple scaling arguments to obtain these gaps. As a consequence the most massive stellar models with masses 1.8 ≤ M/M⊙ ≤ 2 experience slower cooling by hyperonic dUrca processes which involve Λ’s and protons.

First Determination of the Level Structure of an sd-Shell Hypernucleus, _{Λ}^{19}F.

We report on the first observation of γ rays emitted from an sd-shell hypernucleus, _{Λ}^{19}F. The energy spacing between the ground state doublet, 1/2^{+} and 3/2^{+} states, of _{Λ}^{19}F is determined to be 315.5±0.4(stat)_{-0.5}^{+0.6}(syst) keV by measuring the γ-ray energy of the M1(3/2^{+}→1/2^{+}) transition. In addition, three γ-ray peaks are observed and assigned as E2(5/2^{+}→1/2^{+}), E1(1/2^{-}→1/2^{+}), and E1(1/2^{-}→3/2^{+}) transitions. The excitation energies of the 5/2^{+} and 1/2^{-} states are determined to be 895.2±0.3(stat)±0.5(syst) and 1265.6±1.2(stat)_{-0.5}^{+0.7}(syst) keV, respectively. It is found that the ground state doublet spacing is well described by theoretical models based on existing s- and p-shell hypernuclear data.

Examination of strangeness instabilities and effects of strange meson couplings in dense strange hadronic matter and compact stars

Background : The emergence of hyperon degrees of freedom in neutron star matter has been associated to first order phase transitions in some phenomenological models, but conclusions on the possible physical existence of an instability in the strangeness sector are strongly model dependent. Purpose : The purpose of the present study is to assess whether strangeness instabilities are related to specific values of the largely unconstrained hyperon interactions, and to study the effect of the strange meson couplings on phenomenological properties of neutron stars and supernova matter, once these latter are fixed to fulfill the constraints imposed by hypernuclear data. Method : We consider a phenomenological RMF model sufficiently simple to allow a complete exploration of the parameter space. Results : We show that no instability at supersaturation density exists for the RMF model, as long as the parameter space is constrained by basic physical requirements. This is at variance with a non-relativistic functional, with a functional behavior fitted through ab-initio calculations. Once the study is extended to include the full octet, we show that the parameter space allows reasonable radii for canonical neutron stars as well as massive stars above two-solar mass, together with an important strangeness content of the order of 30\%, slightly decreasing with increasing entropy, even in the absence of a strangeness driven phase transition. Conclusions : We conclude that the hyperon content of neutron stars and supernova matter cannot be established with present constraints, and is essentially governed by the unconstrained coupling to the strange isoscalar meson.

The Equation of State for the Nucleonic and Hyperonic Core of Neutron Stars

AbstractWe re-examine the equation of state for the nucleonic and hyperonic inner core of neutron stars that satisfies the 2M⊙ observations as well as the recent determinations of stellar radii below 13 km, while fulfilling the saturation properties of nuclear matter and finite nuclei together with the constraints on the high-density nuclear pressure coming from heavy-ion collisions. The recent nucleonic FSU2R and hyperonic FSU2H models are updated in order to improve the behaviour of pure neutron matter at subsaturation densities. The corresponding nuclear matter properties at saturation, the symmetry energy, and its slope turn out to be compatible with recent experimental and theoretical determinations. We obtain the mass, radius, and composition of neutron stars for the two updated models and study the impact on these properties of the uncertainties in the hyperon–nucleon couplings estimated from hypernuclear data. We find that the onset of appearance of each hyperon strongly depends on the hyperon–nuclear uncertainties, whereas the maximum masses for neutron stars differ by at most 0.1M⊙, although a larger deviation should be expected tied to the lack of knowledge of the hyperon potentials at the high densities present in the centre of 2M⊙ stars. For easier use, we provide tables with the results from the FSU2R and FSU2H models for the equation of state and the neutron star mass–radius relation.

HYPERNUCLEAR MATTER IN COMPACT STARS

We discuss the recently developed energy density functional for hypernuclear matter, which is based on simultaneous calculation of heavy single-$\Lambda$ hypernuclei and compact stars containing hypernuclear core. The nucleonic matter is described in terms of a density-dependent parametrization of nucleon-meson couplings, whereas the hyperonmeson couplings are deduced from the octet model. We identify the parameter space of hyperon-meson couplings for which massive stellar configurations with $M \leq 2.1 M_\odot$ exist and at the same time the laboratory $\Lambda$-hypernuclear data can be described.

Double-Λ hypernuclei within a Skyrme–Hartree–Fock approach

We extend our Skyrme–Hartree–Fock (SHF) approach, which was used earlier to describe successfully the single-Λ hypernuclei, to investigate the binding and the ΛΛ bond energies of the double-Λ hypernuclei. The nucleon–nucleon (NN) and Λ-nucleon (ΛN) interactions are taken from our previous study. For the ΛΛ force, several Skyrme-like potentials available in the literature have been used. We discuss the sensitivity of the calculated ΛΛ binding and bond energies to the ΛΛ and ΛN force parameters. It is found that the existing ΛΛ hypernuclear data do not allow to distinguish between various ΛΛ force parameter sets used by us. However, they show some selectivity for a particular set of the ΛN potential determined in our previous work.

Physics input for modelling superfluid neutron stars with hyperon cores

Observations of massive ($M \approx 2.0~M_\odot$) neutron stars (NSs), PSRs J1614-2230 and J0348+0432, rule out most of the models of nucleon-hyperon matter employed in NS simulations. Here we construct three possible models of nucleon-hyperon matter consistent with the existence of $2~M_\odot$ pulsars as well as with semi-empirical nuclear matter parameters at saturation, and semi-empirical hypernuclear data. Our aim is to calculate for these models all the parameters necessary for modelling dynamics of hyperon stars (such as equation of state, adiabatic indices, thermodynamic derivatives, relativistic entrainment matrix, etc.), making them available for a potential user. To this aim a general non-linear hadronic Lagrangian involving $\sigma\omega\rho\phi\sigma^\ast$ meson fields, as well as quartic terms in vector-meson fields, is considered. A universal scheme for calculation of the $\ell=0,1$ Landau Fermi-liquid parameters and relativistic entrainment matrix is formulated in the mean-field approximation. Use of this scheme allow us to obtain numerical tables with the equation of state, Landau quasiparticle effective masses, adiabatic indices, the $\ell=0,1$ Landau Fermi-liquid parameters, and the relativistic entrainment matrix for the selected models of nucleon-hyperon matter. These data are available on-line and suitable for numerical implementation in computer codes modelling various dynamical processes in NSs, in particular, oscillations of superfluid NSs and their cooling.

Three-body couplings in RMF and its effects on hyperonic star equation of state

We develop a relativistic mean field (RMF) model with explicit three-body couplings and apply it to hyperonic systems and neutron star matter. Three-baryon repulsion is a promising ingredient to answer the massive neutron star puzzle; when strange hadrons such as hyperons are taken into account, the equation of state (EOS) becomes too soft to support the observed two-solar-mass neutron star. We demonstrate that it is possible to consistently explain the massive neutron star and hypernuclear data when we include three-body couplings and modify the hyperon–vector meson couplings from the flavor SU(3) value.

Hyperons in neutron-star cores and a 2 M⊙pulsar

Recent measurement of mass of PSR J1614-2230 rules out most of existing models of equation of state (EOS) of dense matter with high-density softening due to hyperonization or a phase transition to quark matter or a boson condensate. We look for a solution of an apparent contradiction between the consequences stemming from up-to-date hypernuclear data, indicating appearance of hyperons at 3 nuclear densities and existence of a two-solar-mass neutron star. We consider a non-linear relativistic mean field (RMF) model involving baryon octet coupled to meson fields. An effective lagrangian includes quartic terms in the meson fields. The values of the parameters of the model are obtained by fitting semi-empirical parameters of nuclear matter at the saturation point, as well as potential wells for hyperons in nuclear matter and the strength of the Lambda-Lambda attraction in double-Lambda hypernuclei. We propose a non-linear RMF model which is consistent with up-to-date semiempirical nuclear and hypernuclear data and allows for neutron stars with hyperon cores and M larger than 2 solar masses. The model involves hidden-strangenes scalar and vector mesons, coupled to hyperons only, and quartic terms involving vector meson fields. Our EOS involving hyperons is stiffer than the corresponding nucleonic EOS (with hyperons artificially suppressed) above five nuclear densities. Required stiffening is generated by the quartic terms involving hidden-strangeness vector meson.

Hypernuclear γ-ray spectroscopy: present status and perspectives

Hypernuclear γ-ray spectroscopy experiments using a germanium detector array, Hyperball, have accumulated precise data on various p-shell Λ hypernuclei. A common parameter set of the spin-dependent effective interaction strengths (Δ, S Λ , S N , and T), which reproduces most of the hypernuclear data, has been determined. In the J-PARC facility, further experiments of hypernuclear γ-ray spectroscopy are planned to be performed.

Baryon-baryon interactions with strangeness studied from hypernuclei

Structure of hypernuclei provides valuable information on baryon-baryon interactions. We have studied the Λ N spin-dependent interactions from precise level structure of p- shell Λ hypernuclei by means of a recently-developed technique of hypernuclear γ -ray spectroscopy with the germanium detector array, Hyperball. The strengths of the spin-spin, spin-orbit, and tensor interactions have been experimentally determined from Li Λ 7 , Be Λ 9 , and O Λ 16 hypernuclear level energies. Consistency check of the strength parameters has been also made with more p -shell hypernuclear data. Experimental results on double Λ hypernuclei and Σ hypernuclei have also provided information on ΛΛ and Σ N interactions.

Hyperon-Mixed Neutron Stars

Hyperon mixing in neutron star matter is investigated by the G-matrix-based effective interaction approach under the attention to use the YN and the YY potentials compatible with hypernuclear data and is shown to occur atdensities relevant to neutron star cores, together with discussions to clarify the mechanism of contamination. It is remarked that developed Y-mixed phase causes a dramatic softening of the neutron star equation of state and leads to the serious problem that the resulting maximum mass M m a x for neutron star model contradicts the observed neutron star mass (M m a x M o b s ) the threshold densities for A and Σ - are pushed to higher density side, from ∼ 2ρ 0 to ∼ 4ρ 0 (ρ 0 being the nuclear density). On the basis of a realistic Y-mixed neutron star model, occurrence of Y-superfluidity essential for hyperon scenario is studied and both of A- and Σ - -superfluids are shown to be realized with their critical temperatures 10 8 - 9 K, meaning that the hyperon is a promising candidate for a fast non-standard cooling demanded for some neutron stars with low surface temperature. A comment is given as to the consequence of less attractive ΛΛ interaction suggested by the NAGARA event 6 Λ Λ He.

The physics of hypernuclei

Aldo Zenoni, Universitii di Brescia and INFN Sezione di Pavia, Brescia, Italy Paola Gianotti, INFN Laboratori Nazionali di Frascati, Frascati, Italy The physics of hypernuclei nuclei (with new quantum numbers), in direction of other exotic nuclear systems (charmed nuclei and so on). A hypernucleus is generally indicated with the symbol of the parent nucleus with the suffix A, indicating that a A particle has replaced a neutron. ~ C means a nuclear system composed of 6 protons, 5 neutrons and one A particle. Three events of double hypernuclei were observed, in which 2 nucleons are substitutedby 2 A particles. One example is ,J. He, a system composed of2 protons, 2 neutrons and 2 A particles. The concept of hypernuclei can be extended to nuclei where a nucleon is replaced by hyperons other than the A one. Experimental evidence was claimed ofthe existence ofE-hypernuclei, in which a nucleon is replaced by a L hyperon. This is rather surprising since, in nuclear matter, the L can decay through a strong interaction process (L + N~A + N) giving very largewidths for the hypernuclear states, unless a strong suppression mechanism is at work. However, the experimental evidence of the existence of narrow L-hypernuclei is rather controversial and only the case of tHe is considered unambiguous. After the very first evidence of hyperfragments in cosmic ray interactions with nuclei, starting from the end of the Sixties, the installation ofbeams ofKmesons at particle accelerators made it possible to study the formation of hypernuclei in the laboratory. Hypernuclei were produced copiouslywith little background, the required negative for A hyperon production being present in the beam. The typical utilized was the strangeness where a neutron hit by a Kis changed into a A hyperon emitting a 1t(K+ n~ A + rr-). The experimental techniques used in these experiments were photographic emulsions and bubble chambers (filled with He or heavy liquids) exposed to Kbeams. These experiments mainly measured the hyperon binding energies, by means of the kinematical analysis of the disintegration star, and observed the principal decay modes of the hypernuclei. Starting from the Seventies, the study ofhypernuclei was continued with Kbeams by means of counter techniques with magnetic spectrometers and the introduction of new particle detectors (multiwire proportional chambers and drift chambers). The identification ofwell defined excited hypernuclear levels, by means of the kinematical analysis of the production reaction, was one of the most important results of a first series of experiments started at CERN and continued at Brookhaven (USA). The physical interpretation ofthese spectra was possible in terms of microscopic descriptions of the A-nucleus and A-nucleon potentials. In the Eighties, a new technique for hypernucleus production was introduced at the Brookhaven laboratory,bymeans ofintense beams ofhigh energy 1t+. With this technique the A hyperon is produced inside the nucleus by an associated production reaction (1t+ + n ~ A + K+). This has a reduced cross section, compared to the strangeness exchange reaction, however this drawback is over compensated by the greater intensities of the 1t+ beams. The technique was fully exploited at the KEK laboratory in Japan where, for more than ten years, a great wealth of excellent hypernuclear data were produced, concerning both spectroscopyand decay ofhypernuclei. The interest in these new data has triggered the attention ofthe nuclear physics community and, in the last few years, different laboratories around the world have started a hypernuclear physics program: COSY at Jiilich in Germany, TJNAF at Newport News in USA, Nuclotron in Dubna (Russia). Inparticular, it isworth mentioning the Italian hypernudear project, the FINUDA experiment (acronim of Flsica NUcleare a DAne) at the Laboratori Nazion'. ,.

Necessity of extra repulsion in hypernuclear systems: Suggestion from neutron stars

Neutron star models with hyperon-mixed core are studied by a realistic approach to use the YN and the YY interactions consistent with hypernuclear data. From the compatibility of the theoretical maximum mass with the observed neutron star mass 1.44 M⊙ of PSR1913+16, the necessity of some extra repulsion in hypernuclear systems, e.g., a repulsion from three-body force, is stressed. It is noted that the increase of baryon degrees of freedom to avoid the short-range repulsion effectively is an essential mechanism causing the Y-mixed phase.