We investigated structures of low-lying $0s$-orbit $Λ$ states in $p$-shell $Λ$ hypernuclei ($^A_ΛZ$) by applying microscopic cluster models for nuclear structure and a single-channel folding potential model for a $Λ$ particle. For $A>10$ systems, the size reduction of core nuclei is small, and the core polarization effect is regarded as a higher-order perturbation in the $Λ$ binding. The present calculation qualitatively describes the systematic trend of experimental data for excitation energy change from $^{A-1} Z$ to $^A_ΛZ$, in $A>10$ systems. The energy change shows a clear correlation with the nuclear size difference between the ground and excited states. In $^7_Λ\textrm{Li}$ and $^9_Λ\textrm{Be}$, the significant shrinkage of cluster structures occurs consistently with the prediction of other calculations.
Empirical data on the spectra of light hypernuclei, especially the data from recent gamma-ray experiments, is used to constrain the parameters which govern the p(nucleon)s(Lambda) and p(nucleon)p(Lambda) two-body matrix elements that enter into shell-model calculations.
We introduce a mean field model based on realistic 2-body baryon interactions and calculate spectra of a set of p-shell and sd-shell Λ hypernuclei - 13ΛC, 17ΛO, 21ΛNe, 29ΛSi and 41ΛCa. The hypernuclear spectra are compared with the results of a relativistic mean field (RMF) model and available experimental data. The sensitivity of Λ single-particle energies to the nuclear core structure is explored. Special attention is paid to the effect of spin-orbit ΛN interaction on the energy splitting of the Λ single particle levels 0p3/2 and 0p1/2. In particular, we analyze the contribution of the symme…
Halo Structures in p-Shell Hypernuclei with Natural Orbitals
Technische Universität Darmstadt（达姆施塔特工业大学）；Institut für Kernphysik, Fachbereich Physik, Technische Universität Darmstadt（达姆施塔特工业大学物理系核物理研究所）；Helmholtz Forschungsakademie Hessen für FAIR, GSI Helmholtzzentrum（黑森FAIR亥姆霍兹研究中心GSI亥姆霍兹中心）
We evaluate pionic decay widths of Lambda hypernuclei using a shell model for, both the nuclear bound and the continuum nucleon wave functions in the final state, and distorted waves for the outgoing pion. An excellent agreement with the recent KEK measurement of $π^-$-decay widths of $^{12}_Λ$C and $^{28}_Λ$Si is found. Besides, results for $^{56}_Λ$Fe are consistent with the existing upper bound.
Energy spectra of $0s$-orbit $Λ$ states in $p$-shell $Λ$ hypernuclei ($^{A}_ΛZ$) and those in $^{19}_Λ\textrm{F}$ are studied with the microscopic cluster model and antisymmetrized molecular dynamics using the $G$-matrix effective $ΛN$ ($ΛNG$) interactions. Spin-dependent terms of the ESC08a version of the $ΛNG$ interactions are tested and phenomenologically tuned to reproduce observed energy spectra in $p$-shell $^{A}_ΛZ$. Spin-dependent contributions of the $ΛN$ interactions to spin-doublet splitting and excitation energies are discussed. Energy spectra for unobserved excited states in $p$-s…
Variational calculations for s-shell hypernuclei are performed by explicitly including $Σ$ degrees of freedom. Four sets of YN interactions (SC97d(S), SC97e(S), SC97f(S) and SC89(S)) are used. The bound-state solution of $_Λ^5$He is obtained and a large energy expectation value of the tensor $ΛN-ΣN$ transition part is found. The internal energy of the $^4$He subsystem is strongly affected by the presence of a $Λ$ particle with the strong tensor $ΛN-ΣN$ transition potential.
Information on Lambda-7Li, Lambda-9Be, Lambda-10B, Lambda-11B, Lambda-12C, Lambda-15N, and Lambda-16O from the Ge detector array Hyperball is interpreted in terms of shell-model calculations that include both Lambda and Sigma configurations with p-shell cores. It is shown that the data puts strong constraints on the effective Lambda-N interaction.
We extend the recently developed Jacobi no-core shell model to hypernuclei. Based on the coefficients of fractional parentage for ordinary nuclei, we define a basis where the hyperon is the spectator particle. We then formulate transition coefficients to states that single out a hyperon-nucleon pair which allow us to implement a hypernuclear many-baryon Hamiltonian for $p$-shell hypernuclei. As a first application, we use the basis states and the transition coefficients to calculate the ground states of $^{4}_Λ$He, $^{4}_Λ$H, $^{5}_Λ$He, $^{6}_Λ$He, $^{6}_Λ$Li, and $^{7}_Λ$Li and, additionally…
$0s$-orbit $Λ$ states in $p$-shell double-$Λ$ hypernuclei ($^{\ \,A}_{ΛΛ}Z$), $^{\ \,8}_{ΛΛ}\textrm{Li}$, $^{\ \,9}_{ΛΛ}\textrm{Li}$, $^{10,11,12}_{\ \ \ \ \ ΛΛ}\textrm{Be}$, $^{12,13}_{\ \ ΛΛ}\textrm{B}$, and $^{\,14}_{ΛΛ}\textrm{C}$ are investigated. Microscopic cluster models are applied to core nuclear part and a potential model is adopted for $Λ$ particles. The $Λ$-core potential is a folding potential obtained with effective $G$-matrix $Λ$-$N$ interactions, which reasonably reproduce energy spectra of $^{A-1}_{\,Λ}Z$. System dependence of the $Λ$-$Λ$ binding energies is understood by the…
Grand Accélérateur National d’Ions Lourds (GANIL), CEA/DSM - CNRS/IN2P3（大重离子加速器（GANIL））；Department of Physics, Tohoku University（东北大学物理系）；Nishina Center, RIKEN（理化学研究所西村中心）；Université Paris-Saclay, CNRS/IN2P3, IJClab（巴黎萨克雷大学）；School of Nuclear Science and Technology, University of Chinese Academy of Sciences（中国科学院大学核科学与技术学院）
The interpretation of hypernuclear gamma-ray data for p-shell hypernuclei in terms of shell-model calculations that include the coupling of Lambda- and Sigma-hypernuclear states is briefly reviewed. Next, Lambda 8Li, Lambda 8Be, and Lambda 9Li are considered, both to exhibit features of Lambda-Sigma coupling and as possible source of observed, but unassigned, hypernuclear gamma rays. Then, the feasibility of measuring the ground-state doublet spacing of Lambda 10Be, which, like Lambda 9Li, could be studied via the (K-,pi0 gamma) reaction, is investigated. Structural information relevant to the…
We generalize the Jacobi no-core shell model (J-NCSM) to study double-strangeness hypernuclei. All particle conversions in the strangeness $S=-1,-2$ sectors are explicitly taken into account. In two-body space, such transitions may lead to the coupling between states of identical particles and of non-identical ones. Therefore, a careful consideration is required when determining the combinatorial factors that connect the many-body potential matrix elements and the free-space two-body potentials. Using second quantization, we systematically derive the combinatorial factors in question for $S=0,…
It is shown how the recent shell-model determination of Lambda-N spin dependent interaction terms in Lambda hypernuclei allows for a reliable deduction of Lambda-Lambda separation energies in Lambda-Lambda hypernuclei across the nuclear p shell. Comparison is made with the available data, highlighting 11(Lambda-Lambda)Be and 12(Lambda-Lambda)Be which have been suggested as possible candidates for the KEK-E373 Hida event.
We describe {\it ab initio} calculations of doubly strange, $S=-2$, $s$-shell hypernuclei ($^4_{ΛΛ}$H, $^5_{ΛΛ}$H, $^5_{ΛΛ}$He and $^6_{ΛΛ}$He) as a first attempt to explore the few-body problem of the {\it full}-coupled channel scheme for these systems. The wave function includes $ΛΛ$, $ΛΣ$, $NΞ$ and $ΣΣ$ channels. Minnesota $NN$, D2$^\prime$ $YN$, and simulated $YY$ potentials based on the Nijmegen hard-core model, are used. Bound state solutions of these systems are obtained. We find that a set of phenomenological $B_8B_8$ interactions among the octet baryons in $S=0, -1$ and -2 sectors, wh…
In present study, we search the lambda magic number in hypernuclei within the framework of relativistic mean field theory (RMF) with inclusion of hyperon-nucleon and hyperon-hyperon potentials. Based on one- and two-lambda separation energy and two-lambda shell gap, 2, 8, 14, 18, 20, 28, 34, 40, 50, 58, 68, 70 and 82 are suggested to be the $Λ$ magic number within the present approach. The weakening strength of $Λ$ spin-orbit interaction is responsible for emerging the new lambda shell closure other than the model scheme. The predicted $Λ$ magic numbers are in remarkable agreement with earlier…
Shell-model calculations that include both Lambda and Sigma configurations with p-shell cores are used to interpret gamma-ray transitions in Lambda-7Li, -9Be, -10B, -11B, -12C, -15N, and -16O observed with the Hyperball array of Ge detectors. It is shown that the data puts strong constraints on the spin dependence of the Lambda-N effective interaction and that the Lambda-Sigma coupling plays an important role.
Using the Hartree-Fock plus random-phase-approximation (HF+RPA), we study the impurity effect of $Λ$ hyperon on the collective vibrational excitations of double-$Λ$ hypernuclei. To this end, we employ a Skyrme-type $ΛN$ and $ΛΛ$ interactions for the HF calculations, and the residual interactions for RPA derived with the same interactions. We find that inclusion of two $Λ$ hyperons in $^{16}$O shifts the energy of the collective states towards higher energies. In particular, the energy of the giant monopole resonance of $^{\,\,18}_{ΛΛ}$O, as well as that of $^{210}_{ΛΛ}$Pb, becomes larger. This…
$ΛN$ spin-spin and spin-orbit splittings in low-lying excitation spectra are investigated for $p$-shell $Λ$ hypernuclei on the basis of the microscopic structure calculation within the antisymmetrized molecular dynamics, where the $ΛN$ $G$-matrix interaction derived from the baryon-baryon interaction model ESC (extended soft core) is used. It is found that the ground-state spin-parity is systematically reproduced in the $p$-shell $Λ$ hypernuclei by tuning the $ΛN$ spin-spin and spin-orbit interactions so as to reproduce the experimental data of $^{4}_Λ$H, $^{7}_Λ$Li and $^9_Λ$Be. Furthermore, …
This research article is a follow up of earlier work by M. Ikram et al., reported in International Journal of Modern Physics E {\bf{25}}, 1650103 (2016) wherein we searched for $Λ$ magic numbers in experimentally confirmed doubly magic nucleonic cores in light to heavy mass region (ie.$^{16}O - ^{208}Pb$) by injecting $Λ$'s into them. In present manuscript, working within the state-of-art relativistic mean field theory with inclusion of $ΛN$ and $ΛΛ$ interaction in hypernuclei using the predicted doubly magic nucleonic cores ie. $^{292}$120, $^{304}$120, $^{360}$132, $^{370}$132, $^{336}$138, …
Recent experimental evidence presented by the FINUDA Collaboration for a particle-stable Lambda-6H has stirred renewed interest in charting domains of particle-stable neutron-rich Lambda hypernuclei, particularly for unbound nuclear cores. We have studied within a shell-model approach several neutron-rich Lambda hypernuclei in the nuclear p shell that could be formed in (pi-,K+) or in (K-,pi+) reactions on stable nuclear targets. Hypernuclear shell-model input is taken from a theoretically inspired successful fit of gamma-ray transitions in p-shell Lambda hypernuclei which includes also Lambda…
We present the first ab initio calculations for p-shell single-Lambda hypernuclei. For the solution of the many-baryon problem, we develop two variants of the no-core shell model with explicit $Λ$ and $Σ^+$, $Σ^0$, $Σ^-$ hyperons including $Λ$-$Σ$ conversion, optionally supplemented by a similarity renormalization group transformation to accelerate model-space convergence. In addition to state-of-the-art chiral two- and three-nucleon interactions, we use leading-order chiral hyperon-nucleon interactions and a recent meson-exchange hyperon-nucleon interaction. We validate the approach for s-she…
Applying the sum rule approach, we investigate the energy of a soft dipole motion in $Λ$ hypernuclei, which results from a dipole oscillation of a $Λ$ hyperon against the core nucleus. To this end, we systematically study single-$Λ$ hypernuclei, from $^{16}_{\;\,Λ}$O to $^{208}_{\;\;\;Λ}$Pb, for which the ground state wave function is obtained in the framework of Hartree-Fock method with several Skyrme-type $ΛN$ interactions. Our results indicate that the excitation energy of the soft dipole $Λ$ mode, $E_{sdΛ}$, decreases as the mass number increases. We find that the excitation energy is well…
Charge symmetry breaking (CSB) is particularly strong in the A=4 mirror hypernuclei $_Λ^4$H--$_Λ^4$He. Recent four-body no-core shell model calculations that confront this CSB by introducing $Λ$-$Σ^0$ mixing to leading-order chiral effective field theory hyperon-nucleon potentials are reviewed, and a shell-model approach to CSB in p-shell $Λ$ hypernuclei is outlined.
A nonperturbative field theoretic calculation has been made for the $s$-shell hypernuclei. Here we dress the $Λ$- and $Σ$- hypernuclei with off-mass shell pion pairs. The analysis replaces the scalar isoscalar potential by quantum coherent states. The binding energies of $^{4+nΛ}$He $(n=0,1,2)$ agree quite well with the RMF result of Greiner. The experimental binding energies of $^4$He and $^3$He are reasonably well reproduced in our calculation. A satisfactory description of the relevant experimental $Λ$- and $Σ$- separation energies has been obtained.
Explicit expressions for the parity-violating s-wave and the parity-conserving p-wave contributions to pi- weak-decay rates of Lambda hypernuclei in the 1p shell are given in the weak-coupling limit, to update previous shell-model calculations and to compare with recent pi- spectra and total decay rates measured by the FINUDA Collaboration. A useful sum rule for the summed strength of Lambda_{1s} --> pi- + proton_{1p} weak decays is derived. Fair agreement between experiment and calculations is reached, using the primary s-wave amplitude and Cohen-Kurath nuclear wavefunctions. The role of the …
We explore the systematics of ground-state and excitation energies in singly-strange hypernuclei throughout the helium and lithium isotopic chains --- from $^5_Λ$He to $^{11}_Λ$He and from $^7_Λ$Li to $^{12}_Λ$Li --- 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 vari…
An extended version of the antisymmetrized molecular dynamics to study structure of $p$-$sd$ shell hypernuclei is developed. By using an effective $ΛN$ interaction, we investigate energy curves of $^9_Λ$Be, $^{13}_Λ$C and $^{20,21}_Λ$Ne as function of nuclear quadrupole deformation. Change of nuclear deformation caused by $Λ$ particle is discussed. It is found that the $Λ$ in p-wave enhances nuclear deformation, while that in s-wave reduces it. This effect is most prominent in $^{13}_Λ$C. The possibility of the parity inversion in $^{20}_Λ$Ne is also examined.
The binding energies of baryonic systems with quantum number charm or beauty and neutron excess (or large isospin) are estimated within the bound state version of the chiral topological soliton model. The procedure of the skyrmion rescaling is applied which is of importance for large enough flavor excitation energies (for heavy flavors). Inclusion of the flavor excitation energies into the minimization of the total mass of the baryonic state naturally leads to its decrease, and this effect increases with increasing flavor mass. Our results concerning the binding energies turned out to be partl…
We study the shape of $Λ$ hypernuclei in the full ($β,γ$) deformation plane, including both axially symmetric and triaxial quadrupole deformations. To this end, we use the constrained Skyrme Hartree-Fock+BCS method on the three-dimensional Cartesian mesh. The potential energy surface is analyzed for carbon hypernuclei as well as for sd-shell hypernuclei such as $^{27,29}_Λ$Si and $^{25,27}_Λ$Mg. We show that the potential energy surface in the ($β,γ$) plane is similar to each other between the hypernuclei and the corresponding core nuclei, although the addition of $Λ$ hyperon makes the energy …
We employ a feed-forward artificial neural network to extrapolate at large model spaces the results of {\it ab-initio} hypernuclear No-Core Shell Model calculations for the $Λ$ separation energy $B_Λ$ of the lightest hypernuclei, $^3_Λ$H, $^4_Λ$H and $^4_Λ$He, obtained in computationally accessible harmonic oscillator basis spaces using chiral nucleon-nucleon, nucleon-nucleon-nucleon and hyperon-nucleon interactions. The overfitting problem is avoided by enlarging the size of the input dataset and by introducing a Gaussian noise during the training process of the neural network. We find that a…
We describe full-coupled-channel ab initio calculations among the octet baryons for S=-2 s-shell hypernuclei,_{LambdaLambda}^4H,_{LambdaLambda}^5H and_{LambdaLambda}^6He. The wave function includes Lambda Lambda, Lambda Sigma, N Xi, and Sigma Sigma channels. Minnesota NN, D2^\prime YN and Nijmegen model D simulated YY interactions are used. This is the first attempt to explore the few-body problem of the full-coupled channel scheme for A=4-6, S=-2 multistrangeness hypernuclear systems. Bound state solutions of the Lambda Lambda hypernuclei,_{LambdaLambda}^4H,_{LambdaLambda}^5H and _{LambdaLamb…
We discuss low-lying collective excitations of $Λ$ hypernuclei using the self-consistent mean-field approaches. We first discuss the deformation properties of $Λ$ hypernuclei in the $sd$-shell region. Based on the relativistic mean-field (RMF) approach, we show that the oblate deformation for $^{28}$Si nucleus may disappear when a $Λ$ particle is added to this nucleus. We then discuss the rotational excitations of $^{25}_Λ$Mg nucleus using the three-dimensional potential energy surface in the deformation plane obtained with the Skyrme-Hartree-Fock method. The deformation of $^{25}_Λ$Mg nucleus…
A general shell model formalism for the nonmesonic weak decay of the hypernuclei has been developed.It involves a partial wave expansion of the emitted nucleon waves,preserves naturally the antisymmetrization between the escaping particles and the residual core, and contains as a particular case the weak Lambda-core coupling formalism. The hypernuclei are grouped having in view their A-1 cores, that is in those with even-even, even-odd and odd-odd cores.It is shown that in all three cases the nuclear structure manifests itself basically through Pauli Principle, and very simple expressions are …
Background: The calculation of the hyperon binding energy in hypernuclei is crucial to understanding the interaction between hyperons and nucleons. Purpose: We assess the relative importance of two- and three-body hyperon-nucleon force by studying the effect of the hyperon-nucleon-nucleon interaction in closed shell Λ-hypernuclei from A=5 to 91. Methods: The Λ-binding energy has been calculated using the auxiliary field diffusion Monte Carlo method for the first time, to study light and heavy hypernuclei within the same model. Results: Our results show that including a three-body component in …
In this review we discuss the present status of strange nuclear physics, with special attention to the weak decay of Lambda hypernuclei. The models proposed for the evaluation of the Lambda decay widths are summarized and their results are compared with the data. Despite the recent intensive investigations, the main open problem remains a sound theoretical interpretation of the large experimental values of the ratio G_n/G_p. Although recent works offer a step forward in the solution of the puzzle, further efforts must be invested in order to understand the detailed dynamics of the non-mesonic …
The large charge symmetry breaking (CSB) implied by the $Λ$ binding energy difference $ΔB^{4}_Λ(0^+_{\rm g.s.})\equiv B_Λ(_Λ^4$He)$-$$B_Λ(_Λ^4$H) = 0.35$\pm$0.06 MeV of the $A=4$ mirror hypernuclei ground states, determined from emulsion studies, has defied theoretical attempts to reproduce it in terms of CSB in hyperon masses and in hyperon-nucleon interactions, including one pion exchange arising from $Λ-Σ^0$ mixing. Using a schematic strong-interaction $ΛN\leftrightarrowΣN$ coupling model developed by Akaishi and collaborators for $s$-shell $Λ$ hypernuclei, we revisit the evaluation of CSB …
The relativistic nucleus-nucleus collisions can produce hypernuclei and low-temperature hyper-matter as a result of hyperon capture by nuclear residues and free nucleons. We use the transport, coalescence and statistical models to describe the whole process, and point at the important advantages of such reactions: A broad variety of formed hypernuclei in masses and isospin allows for investigating properties of exotic hypernuclei, as well as the hypermatter both at high and low temperatures. The abundant production of multi-strange nuclei that can give an access to multi-hyperon systems and st…
Previous studies of proton and neutron spectra from Non-Mesonic Weak Decay of eight Lambda-Hypernuclei (A = 5-16) have been revisited. New values of the ratio of the two-nucleon and the one-proton induced decay widths, Gamma_2N/Gamma_p, are obtained from single proton spectra, Gamma_2N/Gamma_p = 0.50 +/- 0.24, and from neutron and proton coincidence spectra, Gamma_2N/Gamma_p = 0.36 +/- 0.14stat +0.05sys -0.04sys , in full agreement with previously published ones. With these values, a method is developed to extract the one-proton induced decay width in units of the free Lambda decay width, Gamm…
We evaluate the coincidence spectra in the nonmesonic weak decay (NMWD) $ΛN\go nN$ of $Λ$ hypernuclei $^{4}_Λ$He, $^{5}_Λ$He, $^{12}_Λ$C, $^{16}_Λ$O, and $^{28}_Λ$Si, as a function of the sum of kinetic energies $E_{nN}=E_n+E_N$ for $N=n,p$. The strangeness-changing transition potential is described by the one-meson-exchange model, with commonly used parameterization. Two versions of the Independent-Particle Shell Model (IPSM) are employed to account for the nuclear structure of the final residual nuclei. They are: (a) IPSM-a, where no correlation, except for the Pauli principle, is taken into…
Having in mind its future extension for theoretical investigations related to charmed nuclei, we develop a relativistic formalism for the nonmesonic weak decay of single-$Λ$ hypernuclei in the framework of the independent-particle shell model and with the dynamics represented by the $(π,K)$ one-meson-exchange model. Numerical results for the one-nucleon-induced transition rates of ${}^{12}_Λ\textrm{C}$ are presented and compared with those obtained in the analogous nonrelativistic calculation. There is satisfactory agreement between the two approaches, and the most noteworthy difference is tha…
The separation energies of the isospin triplet $^7_Λ\mathrm{He}$, $^7_Λ\mathrm{Li^{*}}$, $^7_Λ$Be, and the $T=1/2$ doublet $^8_Λ$Li, $^8_Λ$Be are investigated within the no-core shell model. Calculations are performed based on a hyperon-nucleon potential derived from chiral effective field theory at next-to-leading order. The potential includes the leading charge-symmetry breaking (CSB) interaction in the $Λ$N channel, whose strength has been fixed to the experimentally known difference of the $Λ$ separation energies of the mirror hypernuclei $^4_Λ\mathrm{He}$ and $^4_Λ\mathrm{H}$. It turns ou…
We have systematically investigated the excitation spectra of $p$-shell hypernuclei within the shell model based on the nucleon-nucleon and hyperon-nucleon interactions. For the effective nucleon-nucleon interaction, we adopt the Gogny force instead of the widely-used empirical $p$-shell Cohen-Kurath interaction, while the hyperon-nucleon interaction takes the $ΛN$ interaction including the $ΛN$-$ΣN$ coupling effect. We find that the shell model with the Gogny force can give reasonable descriptions of both spectra and binding energies of the $p$-shell nuclei. With this confidence, combined wit…
Taking the hypernucleus $^{13}_{~Λ}$C as an example, we illustrate the miscroscopic particle-rotor model for low-lying spectra of hypernuclei. This approach is based on the beyond-mean-field method, with the particle number and angular momentum projections. The quantum fluctuation of the mean-field is also taken into account for the core nucleus using the generator coordinate method. We show that the impurity effect of $Λ$ hyperon, such as a change in $B(E2)$, is well described with this model. Our calculation indicates that the most important impurity effect in $sd$-shell hypernuclei is a cha…
The impurity effect of hyperon on atomic nuclei has received a renewed interest in nuclear physics since the first experimental observation of appreciable reduction of $E2$ transition strength in low-lying states of hypernucleus $^{7}_Λ$Li. Many more data on low-lying states of $Λ$ hypernuclei will be measured soon for $sd$-shell nuclei, providing good opportunities to study the $Λ$ impurity effect on nuclear low-energy excitations. We carry out a quantitative analysis of $Λ$ hyperon impurity effect on the low-lying states of $sd$-shell nuclei at the beyond-mean-field level based on a relativi…
Ongoing progress in understanding and evaluating charge symmetry breaking in $Λ$ hypernuclei is discussed in connection to recent measurements of the $_Λ^{4}{\rm H}(0^+_{\rm g.s.})$ binding energy at MAMI [A1 Collaboration: PRL 114 (2015) 232501] and of the $_Λ^{4}{\rm He}(1^+_{\rm exc})$ excitation energy at J-PARC [E13 Collaboration: PRL 115 (2015) 222501].
After a short introduction to the nonmesonic weak decay (NMWD) $ΛN\go nN$ of $Λ$-hypernuclei we discuss the long-standing puzzle on the ratio $Γ_n/Γ_p$, and some recent experimental evidences that signalized towards its final solution. Two versions of the Independent-Particle-Shell-Model (IPSM) are employed to account for the nuclear structure of the final residual nuclei. They are: (a) IPSM-a, where no correlation, except for the Pauli principle, is taken into account, and (b) IPSM-b, where the highly excited hole states are considered to be quasi-stationary and are described by Breit-Wigner …
We report on a novel ab initio approach for nuclear few- and many-body systems with strangeness. Recently, we developed a relevant no-core shell model technique which we successfully applied in first calculations of lightest $Λ$ hypernuclei. The use of a translationally invariant finite harmonic oscillator basis allows us to employ large model spaces, compared to traditional shell model calculations, and use realistic nucleon-nucleon and nucleon-hyperon interactions (such as those derived from EFT). We discuss formal aspects of the methodology, show first demonstrative results for ${}_Λ^3$H, $…
We present a study of the nonmesonic weak decay (NMWD) of charmed hypernuclei using a relativistic formalism. We work within the framework of the independent particle shell model and employ a ($π$,$K$) one-meson-exchange model for the decay dynamics. We implement a fully relativistic treatment of nuclear recoil. Numerical results are obtained for the one-neutron-induced transition NMWD rates of the $_{Λ^{+}_{c}}^{12}$N. The effect of nuclear recoil is sizable and goes in the direction to decrease the nuclear decay rate. We found that the NMWD decay rate of $_{Λ^{+}_{c}}^{12}$N is of the same o…
A Multi-Channel Algebraic Scattering (MCAS) approach has been used to analyze the spectra of two hyper-nuclear systems, Lambda-9Be and Lambda-13C. The splitting of the two odd-parity excited levels (1/2^- and 3/2^-) at 11 MeV excitation in Lambda-13C is driven mainly by the weak Lambda-nucleus spin-orbit force, but the splittings of the 3/2^+ and 5/2^+ levels in both Lambda-9Be and Lambda-13C have a different origin. These cases appear to be dominated by coupling to the collective 2+ states of the core nuclei. Using simple phenomenological potentials as input to the MCAS method, the observed s…
The relation of the shell, collective and cluster models of the atomic nuclei is discussed from the viewpoint of symmetries. In the fifties the U(3) symmetry was found as their common part for a single shell problem. For multi major-shell excitations, considered here, the U(3)$\otimes$U(3) dynamical symmetry turns out to be their intersection.
We present a detailed formalism of the microscopic particle-rotor model for hypernuclear low-lying states based on a covariant density functional theory. In this method, the hypernuclear states are constructed by coupling a hyperon to low-lying states of the core nucleus, which are described by the generator coordinate method (GCM) with the particle number and angular momentum projections. We apply this method to study in detail the low-lying spectrum of $^{13}_{~Λ}$C and $^{21}_{~Λ}$Ne hypernuclei. We also briefly discuss the structure of $^{155}_{~~Λ}$Sm as an example of heavy deformed hyper…
We report on ab-initio NCSM calculations of the A=4 mirror Lambda hypernuclei Lambda-4H and Lambda-4He, using the Bonn-Juelich LO chiral EFT YN potentials plus a CSB Lambda0--Sigma0 mixing vertex. In addition to reproducing rather well the 0+ (g.s.) and 1+ (exc.) binding energies, these four-body calculations demonstrate for the first time that the observed CSB splitting of mirror levels, reaching hundreds of keV for 0+ (g.s.), can be reproduced using realistic theoretical interaction models, although with a non-negligible momentum cutoff dependence. Our results are discussed in relation to re…
