YN Interactions Research Articles

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.

Study of the hyperon-nucleon interaction via final-state interactions in exclusive reactions

A novel approach that allows access to long-sought information on the Hyperon-Nucleon (YN) interaction was developed by producing a hyperon beam within a few-body nuclear system, and studying final-state interactions. The determination of polarisation observables, and specifically the beam spin asymmetry, in exclusive reactions allows a detailed study of the various final-state interactions and provides us with the tools needed to isolate kinematic regimes where the YN interaction dominates. High-statistics data collected using the CLAS detector housed in Hall-B of the Thomas Jefferson laboratory allows us to obtain a large set of polarisation observables and place stringent constraints on the underlying dynamics of the YN interaction.

Implications of an increased Λ-separation energy of the hypertriton

Stimulated by recent indications that the binding energy of the hypertriton could be significantly larger than so far assumed, requirements of a more strongly bound HΛ3 state for the hyperon-nucleon interaction and consequences for the binding energies of A=4,5 and 7 hypernuclei are investigated. As basis, a YN potential derived at next-to-leading order in chiral effective field theory is employed. Faddeev and Yakubovsky equations are solved to obtain the corresponding 3- and 4-body binding energies, respectively, and the Jacobi no-core shell model is used for Λ5He and Λ7Li. It is found that the spin-singlet Λp interaction would have to be much more attractive which can be, however, accommodated within the bounds set by the available Λp scattering data. The binding energies of the HeΛ4 hypernucleus are predicted to be closer to the empirical values than for YN interactions that produce a more weakly bound HΛ3. The quality of the description of the separation energy and excitation spectrum for Λ7Li remains essentially unchanged.

Effect of a realistic three-body force on the spectra of medium-mass hypernuclei

We adopt the Hartree–Fock method in the proton–neutron-Λ formalism and the nucleon-Λ Tamm–Dancoff approximation to study the energy spectra of medium-mass hypernuclei. The formalism is developed for a potential derived from effective field theories which includes explicitly the 3-body NNN forces plus the YN LO potential. The energy spectra of selected medium-mass hypernuclei are presented and their properties discussed. The present calculation is the first step of a project devoted to ab initio studies of hypernuclei in medium and heavy mass regions. This may provide a guide for a better understanding of the YN interactions at momentum scales not accessible in few-body hypernuclei.

Hypernuclear no-core shell model

We extend the No-Core Shell Model (NCSM) methodology to incorporate strangeness degrees of freedom and apply it to single-$\Lambda$ hypernuclei. After discussing the transformation of the hyperon-nucleon (YN) interaction into Harmonic-Oscillator (HO) basis and the Similarity Renormalization Group transformation applied to it to improve model-space convergence, we present two complementary formulations of the NCSM, one that uses relative Jacobi coordinates and symmetry-adapted basis states to fully exploit the symmetries of the hypernuclear Hamiltonian, and one working in a Slater determinant basis of HO states where antisymmetrization and computation of matrix elements is simple and to which an importance-truncation scheme can be applied. For the Jacobi-coordinate formulation, we give an iterative procedure for the construction of the antisymmetric basis for arbitrary particle number and present the formulae used to embed two- and three-baryon interactions into the many-body space. For the Slater-determinant formulation, we discuss the conversion of the YN interaction matrix elements from relative to single-particle coordinates, the importance-truncation scheme that tailors the model space to the description of the low-lying spectrum, and the role of the redundant center-of-mass degrees of freedom. We conclude with a validation of both formulations in the four-body system, giving converged ground-state energies for a chiral Hamiltonian, and present a short survey of the $A\le7$ hyper-helium isotopes.

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.

Decay Pion Spectroscopy of Electro-Produced Hypernuclei

The investigation of light hypernuclei is quite important for understanding the basic YN interaction and the mechanism of hypernuclear structure. We started the commissioning of the decay pion spectroscopy of light hypernuclei at MAMI-C in 2011. In order to realize the K+ tagging efficiently, some detectors on KAOS spectrometer were upgraded or newly installed. The existing and well-studied spectrometers, SpekA, SpekC were used as pion spectrometers. The analysis is ongoing to estimate the detectors performance and develop the spectrometers for future experiments with higher beam intensity. The preliminary results of the particle identification are presented in this article.

The mixing of scalar mesons and the baryon-baryon interaction

By introducing the mixing of scalar mesons in the chiral SU(3) quark model, we dynamically investigate the baryon-baryon interaction. The hyperon-nucleon and nucleon-nucleon interactions are studied by solving the resonating group method (RGM) equation in a coupled-channel calculation. In our present work, the experimental lightest pseudoscalar $ \pi$ , K, $ \eta$ , $ \eta^{{\prime}}_{}$ mesons correspond exactly to the chiral nonet pseudoscalar fields $ \pi$ , K, $ \eta$ , $ \eta^{{\prime}}_{}$ in the chiral SU(3) quark model. The $ \eta$ , $ \eta^{{\prime}}_{}$ mesons are considered as the mixing of singlet and octet mesons, and the mixing angle $ \theta_{{ps}}^{}$ is taken to be -23° . For scalar nonet mesons, we suppose that there exists a correspondence between the experimental lightest scalar f 0(600) , $ \kappa$ , a 0(980) , f 0(980) mesons and the theoretical scalar nonet $ \sigma$ , $ \kappa$ , $ \sigma^{{\prime}}_{}$ , $ \epsilon$ fields in the chiral SU(3) quark model. For scalar mesons, we consider two different mixing cases: one is the ideal mixing and another is the $ \theta_{s}^{}$ = 19° mixing. The masses of the $ \sigma^{{\prime}}_{}$ and $ \epsilon$ mesons are taken to be 980MeV, which are just the masses of the experimental a 0(980) , f 0(980) mesons. The mass of the $ \sigma$ meson is an adjustable parameter and is decided by fitting the binding energy of the deuteron, the masses of 560MeV and 644MeV are obtained for the ideal mixing and the $ \theta_{s}^{}$ = 19° mixing, respectively. We find that, in order to reasonably describe the YN interactions, the mass of the $ \kappa$ meson is near 780MeV for the ideal mixing. However, we must enhance the mass of the $ \kappa$ meson for the $ \theta_{s}^{}$ = 19° mixing, the 1050MeV is favorably used in the present work. The experimental $ \sigma$ and $ \kappa$ scalar mesons are very strange, both have larger widths. Hence, no matter what kind of mixing is considered, all the masses of scalar mesons we used in the present work seem to be consistent with the present PDG information.

YN and YY interactions from lattice QCD simulations

One of the main motivations for investing human and economic effort in Lattice QCD calculations of nuclear physics quantities is to explore sectors that cannot be accessed experimentally, or which can be measured with only limited precision. Two lines of research where such kind of calculations may have a clear impact are the study of the evolution of supernova and of the structure and decay of conventional and strange nuclei. Key ingredients for both investigations are the low energy interactions among baryons. Unfortunately, due to the short lifetime of hyperons, the interactions among baryons in the strange sector are only approximately known. The unsatisfactory amount of data coming from scattering experiments produces large uncertainties in the scattering amplitudes. Lattice QCD simulations of baryon-baryon interactions can play a crucial role, and points out as a reliable way to obtain complementary information to what can be obtained from experiments involving baryons in the low energy region.

Feshbach Resonance due to Coherent Λ-Σ Coupling in 7ΛHe

Coherent Λ-Σ coupling effect in 7 ΛHe is analyzed within three-body framework of two coupled channels, Λ- t- t and Σ- τ- t, where τ represents trinulceon which is either 3H or 3He. The hyperon-trinucleon ( Yτ) and trinucleon-trinucleon ( ττ) interactions are derived by folding G-matrices of YN and NN interactions with trinucleon density distributions. It is found that the binding energy of 7 ΛHe is 4.04 MeV below the Λ+ t+ t threshold without Λ-Σ coupling and the binding energy is increased to 4.46 MeV when the coupling effect is included. This state is 7.85 MeV above the 6He+Λ threshold and it may have a chance to be observed as a Feshbach resonance in 7Li ( e , e ′ K + ) 7 ΛHe experiment done at Jefferson Lab.

Hypernuclear properties derived from the new interaction model ESC08

The features of the new YN interaction model ESC08 are studied on the basis of the G-matrix theory.

Strangeness [formula omitted] Baryon-Baryon Interaction in Chiral Effective Field Theory

We present frst results for the doubly strange Ξ N and YY interactions ( Y = Λ , Σ ) obtained within a chiral effective feld theory (EFT) approach based on the Weinberg power counting, by relating the S = − 2 baryon-baryon interactions via SU(3) flavor symmetry to an YN interaction likewise derived within chiral EFT.

Structure of p-shell hypernuclei and the spin-dependence of YN interactions from γ-ray spectroscopy

Shell-model calculations that include both Λ and Σ configurations with p-shell cores are used to interpret γ-ray transitions in Li Λ 7 , Be Λ 9 , B Λ 10 , B Λ 11 , C Λ 12 , N Λ 15 , and O Λ 16 observed with the Hyperball array of Ge detectors. It is shown that the data puts strong constraints on the spin dependence of the Λ N effective interaction.

HYPERON DENSITY DEPENDENCE OF HYPERON-NUCLEON INTERACTIONS IN NEUTRON STARS

The hyperon density dependence (YDD) of hyperon-nucleon interactions are studied in the relativistic mean field (RMF) model and their influences on the properties of neutron stars are studied. The extended RMF considered the interior quarks coordinates of hyperon and bring a hyperon density dependent factor, f(ρY), to the meson-hyperon coupling vertexes. The hyperon density dependence of YN interaction affect the properties of neutron stars only after the corresponding hyperon appears. Then, the influences of the density dependence factors are almost ignored at low densities, which are clear at high densities. The compositions and properties of neutron stars are studied with and without the YDD of YN interactions for the different Σ--nucleus effective potentials, (30, 0, -30)MeV. The calculated results indicated that the YDD of YN interaction soften the equation of state of neutron stars at high densities.

Hyperon-nucleon single-particle potentials with low-momentum interactions

Single-particle potentials in Hartree-Fock approximation for different hyperon-nucleon (YN channels are calculated in the framework of the effective low-momentum YN interaction $\ensuremath{V_{{\rm low} k}}$ . In contrast to the nucleon-nucleon interaction, the available experimental data for the YN interaction are scarce. As a consequence, no unique YN low-momentum potential $\ensuremath{V_{{\rm low} k}}$ can be predicted from the various bare potentials. The resulting momentum- and density-dependent single-particle potentials for several different bare OBE models and for chiral effective field theory are compared to each other.

Extended-soft-core baryon-baryon model. II. Hyperon-nucleon interaction

The YN results are presented from the extended soft-core (ESC) interactions. They consist of local and nonlocal potentials because of (i) one-boson exchanges (OBE), which are the members of nonets of pseudoscalar, vector, scalar, and axial mesons; (ii) diffractive exchanges; (iii) two-pseudoscalar exchange; and (iv) meson-pair exchange (MPE). Both the OBE and pair vertices are regulated by Gaussian form factors producing potentials with a soft behavior near the origin. The assignment of the cutoff masses for the baryon-baryon-meson (BBM) vertices is dependent on the SU(3) classification of the exchanged mesons for OBE and a similar scheme for MPE. The particular version of the ESC model, called ESC04 [T. A. Rijken, Phys. Rev. C 73, 044007 (2006)], describes nucleon-nucleon (NN) and hyperon-nucleon (YN) interactions in a unified way using broken SU(3) symmetry. Novel ingredients are the inclusion of (i) the axial-vector meson potentials and (ii) a zero in the scalar- and axial-vector meson form factors. These innovations made it possible for the first time to keep the parameters of the model close to the predictions of the ${}^{3}{P}_{0}$ quark-antiquark creation model. This is also the case for the $F/(F+D)$ ratios. Furthermore, the introduction of the zero helped to avoid the occurrence of unwanted bound states. Broken SU(3) symmetry serves to connect the NN and the YN channels, which leaves after fitting NN only a few free parameters for the determination of the YN interactions. In particular, the meson-baryon coupling constants are calculated via SU(3) using the coupling constants of the NN analysis as input. Here, as a novel feature, medium-strong flavor-symmetry breaking (FSB) of the coupling constants was allowed, using the ${}^{3}{P}_{0}$ model with a Gell-Mann-Okubo hypercharge breaking for the BBM coupling. Very good fits for ESC model with and without FSB were obtained. The charge-symmetry breaking in the $\ensuremath{\Lambda}p$ and $\ensuremath{\Lambda}n$ channels, which is an SU(2) isospin breaking, is included in the OBE, TME, and MPE potentials. Simultaneous fits to the NN- and the YN-scattering data are described, using different options for the ESC model. For the selected 4233 NN data with energies $0\ensuremath{\le}{T}_{\mathrm{lab}}\ensuremath{\le}350$ MeV, a ${\ensuremath{\chi}}^{2}/{N}_{\mathrm{data}}=1.22$ was typically reached. For the usual set of 35 YN data and 3 ${\ensuremath{\Sigma}}^{+}p$ cross sections from a recent KEK experiment E289 ${\ensuremath{\chi}}^{2}/{\mathit{YN}}_{\mathrm{data}}\ensuremath{\approx}0.63$ was obtained. In particular, we were able to fit the precise experimental datum ${r}_{R}=0.468\ifmmode\pm\else\textpm\fi{}0.010$ for the inelastic capture ratio at rest rather well. The four versions (a,b,c, and d) of ESC04 presented in this article, give different results for hypernuclei. The reported G-matrix calculations are performed for YN ($\ensuremath{\Lambda}N,\ensuremath{\Sigma}N,\ensuremath{\Xi}N$) pairs in nuclear matter. The obtained well depths (${U}_{\ensuremath{\Lambda}},{U}_{\ensuremath{\Sigma}},{U}_{\ensuremath{\Xi}}$) reveal distinct features of ESC04a--d. The $\ensuremath{\Lambda}\ensuremath{\Lambda}$ interactions are demonstrated to be consistent with the observed data of ${}_{\ensuremath{\Lambda}\ensuremath{\Lambda}}^{6}$He. The possible three-body effects are investigated by considering phenomenologically the changes of the vector-meson masses.

Low-momentum hyperon-nucleon interactions

We present a first exploratory study for hyperon-nucleon interactions using renormalization group techniques. The effective two-body low-momentum potential V_low-k is obtained by integrating out the high-momentum components from realistic Nijmegen YN potentials. A T-matrix equivalence approach is employed, so that the low-energy phase shifts are reproduced by V_low-k up to a momentum scale Lambda ~ 500 MeV. Although the various bare Nijmegen models differ somewhat from each other, the corresponding V_low-k interactions show convergence in some channels, suggesting a possible unique YN interaction at low momenta.

Strangeness production in pp and pn reactions at COSY

The cooler synchrotron COSY-Jülich delivers phase-space cooled, polarized proton and deuteron beams with momenta up to p = 3.65 GeV / c . Various experiments on hadron-induced strangeness production on proton, neutron and nuclear targets have been carried out. Here we report recent results on associated strangeness production in p p → K Y N ( Y = Λ , Σ ) reactions, on K + -production in pn collisions, and on K K ¯ -pair production in pp interactions. We also briefly discuss possible measurements to disentangle the parity of the recently discovered pentaquark state Θ + , the spin dependence of the YN interaction, as well as planned experiments which aim at the determination of the a 0 – f 0 mixing matrix element, a quantity which is believed to be sensitive to the nature of the light scalar mesons a 0 / f 0 ( 980 ) .

Hypernuclear structure from γ-ray spectroscopy

The energies of p-shell hypernuclear γ rays obtained from recent experiments using the Hyperball at BNL and KEK are used to constrain the YN interaction which enters into shell-model calculations that include both Λ and Σ configurations.

Faddeev calculation of the hypertriton in the quark-model NN and YN interactions

Faddeev calculation of the hypertriton in the quark-model NN and YN interactions