Light Hypernuclei Research Articles

Analytic continuation in the coupling constant for resonances in ${}^9_{\Lambda}$Be

Abstract The application scope of the analytic continuation in the coupling constant (ACCC) can be extended to the exchange parameters of the effective nucleon-nucleon interaction in microscopic cluster model. Based on such exchange parameter dependent ACCC (abbreviated as EPD-ACCC), we study the ${}_{\Lambda}^9$Be system in the framework of $\alpha+\alpha+\Lambda$ microscopic cluster model. The resonant states of $\alpha+\alpha+\Lambda$ are obtained through EPD-ACCC. Meanwhile, the complex scaling method (CSM) is applied as a comparison. A good agreement between these two theoretical approaches is obtained. This work demonstrate a reliable method EPD-ACCC for estimating the multi-cluster resonances in light hypernuclei.

Light hypernuclei at the boundary of neutron stability

Light hypernuclei at the boundary of neutron stability

Softening of the hypertriton transverse momentum spectrum in heavy-ion collisions

Understanding the properties of hypernuclei helps to constrain the interaction between hyperon and nucleon, which is known to play an essential role in determining the properties of neutron stars. Experimental measurements have suggested that the hypertriton (HΛ3), the lightest hypernucleus, exhibits a halo structure with a deuteron core encircled by a Λ hyperon at a distance of about 10 fm. This large Λ−d distance in HΛ3 wave function is found to cause a suppressed HΛ3 yield and a softening of its transverse momentum (pT) spectrum in relativistic heavy-ion collisions. Within the coalescence model based on nucleons and Λ hyperons from a microscopic hybrid hydro model with a hadronic afterburner for nuclear cluster production in Pb-Pb collisions at sNN= 5.02 TeV, we show how this softening of the hypertriton pT spectrum appears and leads to a smaller mean pT for HΛ3 than for helium-3 (3He). The latter is opposite to the predictions from the blast-wave model which assumes that HΛ3 and 3He are thermally produced at the kinetic freeze-out of heavy-ion collisions. The discovered quantum mechanical softening of the (anti-)hypertriton spectrum can be experimentally tested in relativistic heavy-ion collisions at different collision energies and centralities and used to obtain valuable insights to the mechanisms for light (hyper-)nuclei production in these collisions.

Light and hyper nuclei formation at [formula omitted] 3 GeV Au+Au collisions using Wigner coalescence approach

The production of light nuclei and hyper-nuclei in heavy-ion collisions, particularly at high baryon density, is crucial for understanding the dynamical evolution of the collision system and exploring the internal state of nuclear matter of compacted stellar object. Despite being a topic of ongoing debate, an improved theoretical understanding is necessary. In this work, production of light nuclei (d, t, 3He, 4He) and hyper-nuclei (Λ3H, Λ4H) was investigated using the JAM microscopic transport model combined with an afterburner coalescence process at sNN= 3 GeV Au+Au collisions. The formation of a specific nucleus during the coalescence process is determined by its Wigner function. The comparison of the calculations for pT spectra, average pT, and rapidity distributions to the measurements from the STAR experiment was performed. We investigated the dynamic information carried by light nuclei and determined the averaged spatial distance 〈ΔR〉 and momentum difference 〈ΔP〉 of constituent nucleons (Λ) for each nucleus species.

Exotic particles and nuclei

Light nuclei, antinuclei and hypernuclei constitute a laboratory to study the mechanisms of formation of bound states in proton-proton and nucleus-nucleus collisions over a broad range of collision energies, providing insights into the nuclear structure as well as into the strong interaction. In this contribution, a selection of the experimental results and latest developments presented at the Quark Matter 2023 conference is reviewed.

Hyperon-nucleon interaction constrained by light hypernuclei

Ab initio structure calculations for p-shell hypernuclei have recently become accessible through extensions of nuclear many-body methods, such as the no-core shell model, in combination with hyperon-nucleon interactions from chiral effective field theory. However, the low-energy constants in these hyperon-nucleon interactions are poorly constraint due to the very limited amount of experimental scattering data available. We present a hyperon-nucleon interaction that is additionally constrained by experimental ground-state and spectroscopic data for selected p-shell hypernuclei and, thus, optimized for hypernuclear structure calculations. We show that the previous overestimation of the hyperon separation energies in the p-shell is remedied and discuss the significantly improved description of the ▪ isotopic chain. We further discuss the uncertainty quantification for hypernuclear observables on the many-body level, obtained through a novel machine-learning tool.

Results on light (anti)hypernuclei production with ALICE at the LHC

The high collision energies reached at the LHC lead to significant production yields of light (anti)hypernuclei in proton–proton (pp), proton–lead (p–Pb) and, in particular, Pb–Pb collisions. The lightest known hypernucleus is the hypertriton, which is a bound state of a proton, a neutron, and a Λ hyperon. It decays weakly with a decay length of a few centimeters. The excellent tracking and particle identification capabilities of the ALICE detector, exploiting the energy loss measurement of the Time Projection Chamber (TPC) and using the Inner Tracking System (ITS) to distinguish between primary and secondary (decay) vertices, allow for the determination of the hypertriton yield across different collision systems, its lifetime, and its binding energy. The latest hypertriton lifetime measurement in Pb–Pb collisions performed in the 2-body decay channel will be presented. This measurement contributes to the solution of the hypertriton lifetime puzzle. In addition, the hypertriton production in different collision systems and at different energies will be compared to model predictions. Due to its low binding energy, and hence to its large size, the hypertriton is the ideal candidate to distinguish between statistical hadronization and coalescence models. With the precision of the presented yield measurements some variants of the aforementioned models can be excluded.

The WASA-FRS project at GSI and its perspective

A novel technique to study bound states of exotic hadrons in subatomic nuclei, such as hypernuclei and mesic nuclei, has been developed by employing the Fragment Separator FRS and the WASA central detector at GSI. Two experiments, S447 for studying light hypernuclei, especially hypertriton and a Λnn bound state, and S490 for searching for η’ mesic-nuclei, were recently performed. Data analyses are currently in progress, and light charged particles such as protons and π± are clearly observed and identified in the both experiments. For S447, light nuclear fragments that can also be residual nuclei from decays of hypernuclei of interests have been analysed by the FRS, and a momentum resolution, Δp/p, of 5×10−4 has been achieved. Further data analyses are to be completed. The WASA-FRS project will be continued and extended with the FRS at FAIR Phase 0, and upgrading of the WASA magnet and detectors is currently in progress. Furthermore, construction of a larger detector system with the Super-FRS at FAIR Phase 1 is also under consideration.

Machine learning light hypernuclei

We employ a feed-forward artificial neural network to extrapolate at large model spaces the results of ab-initio hypernuclear No-Core Shell Model calculations for the Λ separation energy BΛ of the lightest hypernuclei, Λ3H, Λ4H and Λ4He, 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 network with a single hidden layer of eight neurons is sufficient to extrapolate correctly the value of the Λ separation energy to model spaces of size Nmax=100. The results obtained are in agreement with the experimental data in the case of Λ3H and the 0+ state of Λ4He, although they are off of the experiment by about 0.3 MeV for both the 0+ and 1+states of Λ4H and the 1+ state of Λ4He. We find that our results are in excellent agreement with those obtained using other extrapolation schemes of the No-Core Shell Model calculations, showing this that an ANN is a reliable method to extrapolate the results of hypernuclear No-Core Shell Model calculations to large model spaces.

Energy dependence of light hypernuclei production in heavy-ion collisions from a coalescence and statistical-thermal model perspective

A comparison of light hypernuclei production, from Ultra-relativistic Quantum Molecular Dynamics (UrQMD)$+\text{coalescence}$ and the thermal model, in heavy ion collisions over a wide range of beam energies and system sizes is presented. We find that both approaches provide generally similar results, with differences in specific details. Especially the ratios of hypertriton to $\mathrm{\ensuremath{\Lambda}}$ are affected by both the source radius $\mathrm{\ensuremath{\Delta}}r$ of the coalescence procedure as well as canonical effects. On the other hand, the double ratio ${S}_{3}$ is almost independent of canonical effects, which is in contrast to coalescence. Thus, both the beam energy dependence and centrality dependence of ${S}_{3}$ can be used to constrain the hypertriton source radius. To do so the currently available data are not yet sufficient. Elliptic flow is shown to be unaffected by the source size of the nuclei and an almost perfect mass scaling of the elliptic flow is observed. Our predictions further suggest that the existence of the H-dibaryon ($\mathrm{\ensuremath{\Lambda}}\mathrm{\ensuremath{\Lambda}}$) seems ruled out by ALICE data.

Collective flow of light nuclei and hyper-nuclei in Au+Au collisions at √SNN = 3, 14.6, 19.6, 27, and 54.4 GeV using the STAR detector

Light nuclei and hyper-nuclei are produced in abundance in heavyion collisions. The production mechanism of these species in heavy-ion collisions still remains to be understood. In these proceedings, we report the transverse momentum and centrality dependence of elliptic flow (υ2) of d, t, and 3He in Au+Au collisions at √SNN = 14.6, 19.6, 27, and 54.4 GeV. Mass number scaling of υ2(pT) of light nuclei is shown. We also report the first observation of hyper-nuclei Λ3H and Λ4H directed flow (υ1) in √SNN = 3 GeV mid-central (5-40%) Au+Au collisions in the fixed target mode.

Light hypernuclei in heavy-ion collisions

Prediction for hyper nuclei multiplicities from GSI to LHC energies from the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model combined with a final state coalescence approach is presented and compared to the thermal model. The influence of the coalescence radius on the collision energy and centrality dependence of the Λ3H/Λ ratio is discussed.

Measurements on the production and properties of light hypernuclei at STAR

The hyperon-nucleon (Y-N) interaction, an important ingredient for the nuclear equation-of-state (EoS), remains poorly constrained. Precise measurements of hypernucei intrinsic properties and production yields in heavy-ion collisions are crucial for the understanding of their production mechanisms and the strength of the Y-N interaction. Thanks to the high statistics data taken from the STAR BES II program, a series of hypernuclei measurements are carried out at low energies. In these proceedings, we present the kinematic and centrality dependence of light hypernuclei production yields and strangeness population factor (S3, S4) in Au+Au collisions at √SNN = 3 GeV. We also report the energy dependence of Λ3H yields and S3 at mid-rapidity from 3 to 27 GeV Au+Au collisions. Precise measurements of Λ4He lifetime and Λ3H branching ratio are also reported. These results are compared with model calculations and physics implications are discussed.

Study of light hypernuclei in Europe: The hypertriton and nnΛ puzzles

The current understanding of light hypernuclei, which are sub-atomic nuclei with strangeness, is being challenged and studied in detail by several European research groups and collaborations. In recent years, studies of hypernuclei using high-energy heavy ion beams have reported unexpected results on the three-body hypernuclear state 3ΛH, named the hypertriton. For some time, reports of a shorter lifetime and larger binding energy than what was previously accepted have created a puzzling situation for its theoretical description; this is known as the "hypertriton puzzle". With the inclusion of the most recent experimental measurements, the current status of the hypertriton puzzle is evolving. Additionally, the possible neutral bound state of a Λ hyperon with two neutrons, nnΛ, has raised questions about our understanding of the formation of light hypernuclei either in bound or resonance states. These results have initiated several ongoing experimental programs all over the world to study these three-body hypernuclear states precisely. We are studying these light hypernuclear states by employing heavy ion beams at 2AGeV on a fixed carbon target with the WASA detector system and the Fragment Separator (FRS) at GSI. The WASA-FRS experimental campaign was performed during the first quarter of 2022, and this paper presents a short overview of the campaign and how it seeks to tackle the hypertriton and nnΛ puzzles. Data analysis is ongoing, and several preliminary results will be reported.

Investigating the coalescence-inspired sum rule for light nuclei and hypernuclei in heavy-ion collisions

A data-driven idea is presented to test if light nuclei and hypernuclei obey the coalescence-inspired sum rule, i.e., to test if the flow of a light nucleus or hypernucleus is the summed flow of each of its constituents. Here, the mass difference and charge difference among the constituents of light nuclei and hypernuclei are treated appropriately. The idea is applied to the available data for $\sqrt{{s}_{NN}}=3$ GeV fixed-target $\mathrm{Au}+\mathrm{Au}$ collisions at the Relativistic Heavy Ion Collider (RHIC), published by the STAR Collaboration. It is found that the sum rule for light nuclei is approximately valid near midrapidity ($\ensuremath{-}0.3<y<0$), but there is a clear violation of the sum rule at large rapidity ($y<\ensuremath{-}0.3$). The Jet AA Microscopic Transport Model (JAM), with baryonic mean-field plus nucleon coalescence, generates a similar pattern as obtained from the experimental data. In the present approach, the rapidity dependence of directed flow of the hypernuclei ${}_{\mathrm{\ensuremath{\Lambda}}}^{3}\mathrm{H}$ and ${}_{\mathrm{\ensuremath{\Lambda}}}^{4}\mathrm{H}$ is predicted in a model-independent way for $\sqrt{{s}_{NN}}=3$ GeV $\mathrm{Au}+\mathrm{Au}$ collisions, which will be explored by ongoing and future measurements from STAR.

Nuclear physics uncertainties in light hypernuclei

The energy levels of light hypernuclei are experimentally accessible observables that contain valuable information about the interaction between hyperons and nucleons. In this work we study strangeness $S = -1$ systems $^{3,4}_\Lambda$H and $^{4,5}_\Lambda$He using the ab initio no-core shell model (NCSM) with realistic interactions obtained from chiral effective field theory ($\chi$EFT). In particular, we quantify the finite precision of theoretical predictions that can be attributed to nuclear physics uncertainties. We study both the convergence of the solution of the many-body problem (method uncertainty) and the regulator- and calibration data-dependence of the nuclear $\chi$EFT Hamiltonian (model uncertainty). For the former, we implement infrared correction formulas and extrapolate finite-space NCSM results to infinite model space. We then use Bayesian parameter estimation to quantify the resulting method uncertainties. For the latter, we employ a family of 42 realistic Hamiltonians and measure the standard deviation of predictions while keeping the leading-order hyperon-nucleon interaction fixed. Following this procedure we find that model uncertainties of ground-state $\Lambda$ separation energies amount to $\sim 20(100)$ keV in $^3_\Lambda$H($^4_\Lambda$H,He) and $\sim 400$ keV in $^5_\Lambda$He. Method uncertainties are comparable in magnitude for the $^4_\Lambda$H,He $1^+$ excited states and $^5_\Lambda$He, which are computed in limited model spaces, but otherwise much smaller. This knowledge of expected theoretical precision is crucial for the use of binding energies of light hypernuclei to infer the elusive hyperon-nucleon interaction.

Proton drip line for light hypernuclei

Proton drip line for light hypernuclei

Effective two-body ΛN → NN weak potentials deduced from three-body ΛNN → NNN interactions and hypernuclear non-mesonic weak decay rates

Abstract We intend to study the role of the three-body weak ΛNN → NNN interaction in two-nucleon induced hypernuclear non-mesonic weak decay. The three-body weak interactions are constructed on the basis of the meson-pair exchange (MPE) model and then we derive the effective two-body ΛN → NN weak potentials from the three-body interactions based on the Loiseau–Nogami–Ross approximation. The strong coupling constants of MPE are taken from the Nijmegen ESC and GESC models and the weak ones of MPE are evaluated in the weak Λ–n mixing model by Dalitz and Von Hippel [Phys. Lett. 10, 153 (1964)]. The effective two-body ΛN → NN weak potentials are applied to evaluate hypernuclear non-mesonic decay rates, which should give a certain additional contribution to the two-nucleon induced decay rate Γ2N. Calculations of $\Gamma ^{({\text{eff.2B}})}_{nm}$ are done for $^5_\Lambda {\rm He}$, $^{11}_\Lambda {\rm B}$, and $^{12}_\Lambda {\rm C}$ and the results are compared with experimental data $\Gamma ^\mathrm{exp}_{2N}$. We have demonstrated the possibility of accounting for the two-nucleon induced non-mesonic decays of light and p-shell hypernuclei by introducing the effective two-body potentials deduced from the three-body weak interactions, though the calculated $\Gamma ^{(\text{eff.2B})}_{nm}$ still includes uncertainties. Discussions and limitations of our “effective two-body ΛN → NN model” are given.

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.

Heavy baryons in hot stellar matter with light nuclei and hypernuclei

The production of light nuclei and hypernuclei together with heavy baryons, both hyperons and $\Delta$-baryons, in low density matter as found in stellar environments such as supernova or binary mergers is studied within relativistic mean-field models. Five light nuclei were considered together with three light hypernuclei. The presence of both hyperons and $\Delta$-baryons shift the dissolution of clusters to larger densities and increase the abundance of clusters. This effect is larger the smaller the charge fraction and the higher the temperature. The couplings of the $\Delta$-baryons were chosen imposing that the nucleon effective mass remains finite inside neutron stars.