ΛN Interaction Research Articles

Study of Λ hypernuclei using hadron beams and γ-ray spectroscopy at J-PARC

A combination of the production of Λ hypernuclei via hadron beams and their precision γ-ray spectroscopy using a Ge detector array, Hyperball/Hyperball2, has played essential roles in studies of hypernuclear structure. After a brief summary of our previous studies for p-shell hypernuclei at KEK-PS and BNL-AGS, we describe our plans of hypernuclear γ-ray spectroscopy experiments at J-PARC, in particular, the first experiment E13 starting in 2012, in which we further study ΛN interaction and measure Λ-spin-flip B(M1) values using light hypernuclei such as HeΛ4, LiΛ7, BΛ10, BΛ11 and FΛ19.

Structure of studied with the four-body cluster model

Energy levels of the hypernucleus BeΛ10 within the framework of an α+α+Λ+n four-body cluster model are calculated. Interactions between the constituent subunits are determined so as to reproduce reasonably well the observed low-energy properties of the αα, αN, αΛ, ααΛ and ααN subsystems. Furthermore, the two-body ΛN interaction is adjusted so as to reproduce the 0+–1+ splitting of HΛ4. The Λ separation energies of positive parity states are smaller than those of negative parity states. As a result, there occurs level inversion between 0+, 11+ states and 3− and 22− states.

Binding Energy of 7ΛHe and Test of Charge Symmetry Breaking in the ΛN Interaction Potential

The binding energy of 7ΛHe has been obtained for the first time with reaction spectroscopy using the (e, e′K+) reaction at Jefferson Lab's Hall C. A comparison among the binding energies of the A = 7 T = l iso-triplet hypernuclei, 7ΛHe, 7ΛLi*and 7ΛBe, is made and possible charge symmetry breaking (CSB) in the ΛN potential is discussed. For 7ΛHe and 7ΛBe, the shifts in binding energies are opposite to those predicted by a recent cluster model calculation, which assumes that the unexplained part of the binding energy difference between 4ΛH and 4ΛHe, is due to the CSB of the ΛN potential. Further examination of CSB in light hypernuclear systems is required both experimentally and theoretically.

HYPERON-NUCLEUS SYSTEMS IN G-MATRIX APPROACH

In the G-matrix approach, two topics are discussed. One is the spin-dependent components of ΛN interactions. The other is the derivation of Σ-nucleus interactions.

Λ Hypernuclei via γ-Ray Spectroscopy

High precision γ-ray spectroscopy of Λ hypernuclei with a germanium detector array, Hyperball, has revealed fine structure of various p-shell Λ hypernuclei. From accumulated data the strengths of all the spin-dependent components in the ΛN interaction have been extracted, which play essential roles to improve baryon-baryon interaction models. The hypernuclear shrinking effect was confirmed from measurement of a B(E2) value in ΛLi. In the J-PARC facility, intense kaon beams and a new generation Ge detector array will allow us to investigate baryon properties in nuclei and impurity effects, as well as to further study the hyperon-nucleon interactions.

Hypernuclear single particle spectra based on in-medium chiral [formula omitted] dynamics

A previously derived relativistic energy density functional for nuclei, based on low-energy in-medium chiral dynamics, is generalized to implement constraints from chiral SU ( 3 ) effective field theory and applied to Λ hypernuclei. Density-dependent central and spin–orbit mean fields are calculated for a Λ hyperon using the SU ( 3 ) extension of in-medium chiral perturbation theory to two-loop order. Long range ΛN interactions arise from kaon-exchange and from two-pion-exchange with a Σ hyperon in the intermediate state. Short-distance dynamics is encoded in contact interactions. They include scalar and vector mean fields reflecting in-medium changes of quark condensates, constrained by QCD sum rules. The Λ single particle orbitals are computed for a series of hypernuclei from 13 Λ C to 208 Λ Pb. The role of a surface (derivative) term is studied. Its strength is found to be compatible with a corresponding estimate from in-medium chiral perturbation theory. Very good agreement with hypernuclear spectroscopic data is achieved. The smallness of the Λ-nuclear spin–orbit interaction finds a natural explanation in terms of an almost complete cancellation between short-range scalar/vector contributions and longer range terms generated by two-pion exchange.

Gamma-ray spectroscopy of hypernuclei: Recent results and future plans

A series of hypernuclear γ-ray spectroscopy experiments using a germanium detector array, Hyperball, have accumulated precise data on various p-shell Λ hypernuclei. Recently, 12ΛC and 11ΛB were studied at KEK using the (π+,K+γ) reaction, and a transition from a directly-populated spin-flip state, 16ΛO(2−), was observed in BNL E930 data. It is discussed whether the spin-dependent ΛN interaction parameters determined from previous experiments can consistently explain other γ spectroscopy data. At the J-PARC facility, further hypernuclear γ-ray spectroscopy experiments are planned, particularly to measure the g factor of a Λ in a nucleus from a spin-flip B(M1) value and to investigate the ΛN interaction more in detail.

In-medium chiral [formula omitted] dynamics and hypernuclear structure

A previously introduced relativistic energy density functional, successfully applied to ordinary nuclei, is extended to hypernuclei. The density-dependent mean field and the spin–orbit potential are consistently calculated for a Λ hyperon in the nucleus using the SU(3) extension of in-medium chiral perturbation theory. The leading long range ΛN interaction arises from kaon-exchange and 2π-exchange with Σ hyperon in the intermediate state. Scalar and vector mean fields reflecting in-medium changes of the quark condensates are constrained by QCD sum rules. The model, applied to oxygen as a test case, describes spectroscopic data in good agreement with experiment. In particular, the smallness of the Λ spin–orbit interaction finds a natural explanation in terms of an almost complete cancellation between scalar–vector background contributions and long-range terms generated by two-pion exchange.

Hypernuclei and in-medium chiral dynamics

A recently introduced relativistic nuclear energy density functional, constrained by features of low-energy QCD, is extended to describe the structure of hypernuclei. The density-dependent mean field and the spin-orbit potential of a Λ-hyperon in a nucleus, are consistently calculated using the SU(3) extension of in-medium chiral perturbation theory. The leading long-range ΛN interaction arises from kaon-exchange and 2π-exchange with a Σ-hyperon in the intermediate state. Scalar and vector mean fields, originating from in-medium changes of the quark condensates, produce a sizeable short-range spin-orbit interaction. The model, when applied to oxygen as a test case, provides a natural explanation for the smallness of the effective Λ spin-orbit potential: an almost complete cancellation between the background contributions (scalar and vector) and the long-range terms generated by two-pion exchange.

Λ Nuclear physics

We examine briefly whether our realistic models of nuclear forces, which govern the interactions of neutrons and protons with one another and form the basis for precision calculations describing conventional few-nucleon systems, can extrapolate beyond the realm of S = 0 nuclear physics where they were developed, or whether they are merely exquisite interpolation tools within the bounds of well established neutron-proton physics. To address that issue, we examine certain novel aspects of Λ hypernuclei, exploring how few-body hypernuclei provide a laboratory in which one can investigate properties of the ΛN interaction. Finally we look forward to possible future experiments that can enhance our minimal data base for hyperon-nucleon scattering and reactions.

Binding energies of hypernuclei and ΛN interaction

A central ΛN potential VΛN is found on the basis of an analysis of the binding energies of 1s-shell hypernuclei and Λp scattering. Within the exprerimental errors, this potential makes it possible to reproduce the binding energies of three-, four-, and five-particle ground and excited states of hypernuclei and the angular and energy dependences of the cross sections for Λp scattering. The accuracy and reliability of the calculation of three-, four-, and five-particle hypernuclear and the respective nuclear systems is ensured by determining both upper and lower bounds on the energy. Within the Λ plus core model, the potential VΛN is matched with binding energies of heavy hypernuclei.

Binding energies of hypernuclei and ΛN interaction

A central ΛN potential V ΛN that describes, in the limits of experimental errors, the binding energies of three-, four-, and five-particle ground and excited states of hypernuclei, as well as energy and angular dependence of Λp scattering cross sections, is found on the basis of a conjoint analysis of binding energies of 1s-shell hypernuclei and Λp scattering. The reliability and accuracy of three-, four-, and five-particle calculations of hypernuclei and related nuclear systems are assured by the estimation of, an upper, as well as a lower bound of energy. In the framework of the model Λ+core, V ΛN agrees with binding energies of heavy hypernuclei.

Alpha particles accompanying the weak decay of Λ 10 Be and Λ 10 B hypernuclei

The possibility of a detailed investigation of weak ΛN interaction in the Λ10Be and Λ/10B hypernuclei, which stand out owing to their ααNΛ cluster structure, is discussed. The detection of a few groups of correlated αα pairs will furnish information about decays to specific states of product nuclei (8Be*, 8Li, 8B), thereby paving the way to a phenomenological analysis of the weak decays of p-shell hypernuclei. The ratios of the intensities of individual alpha-particle groups to be measured in experiments at the nuclotron of the Joint Institute for Nuclear Research (JINR, Dubna) will provide a useful criterion for choosing an appropriate model of weak ΛN interaction. The current state of hypernuclear physics is briefly reviewed.

The E. coli NusA carboxy‐terminal domains are structurally similar and show specific RNAP‐ and λN interaction

The carboxy-terminal domain of the transcription factor Escherichia coli NusA, NusACTD, interacts with the protein N of bacteriophage lambda, lambdaN, and the carboxyl terminus of the E. coli RNA polymerase alpha subunit, alphaCTD. We solved the solution structure of the unbound NusACTD with high-resolution nuclear magnetic resonance (NMR). Additionally, we investigated the binding sites of lambdaN and alphaCTD on NusACTD using NMR titrations. The solution structure of NusACTD shows two structurally similar subdomains, NusA(353-416) and NusA(431-490), matching approximately two homologous acidic sequence repeats. Further characterization of NusACTD with 15N NMR relaxation data suggests that the interdomain region is only weakly structured and that the subdomains are not interacting. Both subdomains adopt an (HhH)2 fold. These folds are normally involved in DNA-protein and protein-protein interactions. NMR titration experiments show clear differences of the interactions of these two domains with alphaCTD and lambdaN, in spite of their structural similarity.

Three-body models of the 6ΛΛHe and 9ΛBe hypernuclei with non-local interactions

A three-body model involving non-local interactions is developed in configuration space. It is based on a hyperspherical-harmonics expansion and the Lagrange-mesh method. The 6 ΛΛ He and 9 Λ Be hypernuclei are studied as three-body α Λ Λ and α α Λ systems. Recently proposed quark-model based ΛN and ΛΛ interactions are used. A non-local Λα interaction is obtained by folding the ΛN interaction with a Gaussian α density. Various phenomenological αα interactions are employed. The results agree within 1 keV with recent Faddeev calculations in momentum space. Energies and radii of 6 ΛΛ He and 9 Λ Be are compared with a purely local model. The B(E2) between the 9 Λ Be bound states is also calculated. The role of non-locality is discussed.

An EFT for the weak ΛN interaction

The nonleptonic weak | Δ S | = 1 ΛN interaction, responsible for the dominant, nonmesonic decay of all but the lightest hypernuclei, is studied in the framework of an effective field theory. The long-range physics is described through tree-level exchange of the SU(3) Goldstone bosons ( π and K), while the short-range potential is parametrized in terms of lowest-order contact terms obtained from the most general non-derivative local four-fermion interaction. Fitting to available weak hypernuclear decay rates for 5 Λ He, 11 Λ B and 12 Λ C yields reasonable values for the low-energy constants.

Structural basis for the interaction of Escherichia coli NusA with protein N of phage lambda.

The C terminus of transcription factor NusA from Escherichia coli comprises two repeat units, which bind during antitermination to protein N from phage lambda. To delineate the structural basis of the NusA-lambdaN interaction, we attempted to crystallize the NusA C-terminal repeats in complex with a lambdaN peptide (residues 34-47). The two NusA domains became proteolytically separated during crystallization, and crystals contained two copies of the first repeat unit in contact with a single lambdaN fragment. The NusA modules employ identical regions to contact the peptide but approach the ligand from opposite sides. In contrast to the alpha-helical conformation of the lambdaN N terminus in complex with boxB RNA, residues 34-40 of lambdaN remain extended upon interaction with NusA. Mutational analyses indicated that only one of the observed NusA-lambdaN interaction modes is biologically significant, supporting an equimolar ratio of NusA and lambdaN in antitermination complexes. Solution studies indicated that additional interactions are fostered by the second NusA repeat unit, consistent with known compensatory mutations in NusA and lambdaN. Contrary to the RNA polymerase alpha subunit, lambdaN binding does not stimulate RNA interaction of NusA. The results demonstrate that lambdaN serves as a scaffold to closely oppose NusA and the mRNA in antitermination complexes.

Lifetime of heavy hypernuclei and its implications on the weak ΛN interaction

The lifetime of the Λ-hyperon in heavy hypernuclei measured in proton-Au, -Bi and -U collisions by the COSY-13 Collaboration at COSY-Jülich has been analyzed to yield τΛ = (145±11) ps. This value for τΛ is compatible with the lifetime extracted from antiproton annihilation on Bi and U targets, albeit much more accurate. Theoretical models based on the meson exchange picture and assuming the validity of the phenomenological ΔI = 1/2 rule predict the lifetime of heavy hypernuclei to be significantly larger (2-3 standard deviations). Such large differences indicate that at least one of the assumptions in these models is not fulfilled. A much better reproduction of the lifetimes of heavy hypernuclei is achieved in the phase space model, if the ΔI = 1/2 rule is discarded in the nonmesonic Λ decay.

High resolution spectroscopy of Λ hypernuclei: present status and perspectives

Recent results and future directions of the γ-ray spectroscopy of Λ hypernuclei are discussed. A further analysis of the last KEK experiment (E566) has revealed a new γ transition in 12ΛC at 6048keV (preliminary), which is ascribed to the M1(13−→11−) transition. At J-PARC, studies will be extended from p-shell to s-shell and sd-shell hypernuclei. In the first part of the J-PARC E13 experiment, we will measure the 4ΛHe(1+→0+) transition to study charge-symmetry breaking in the ΛN interaction and investigate the 19ΛF hypernucleus to study ΛN spin–spin interaction further using one of the sd-shell hypernuclei. In the second part of E13, we will precisely measure the spin-flip B(M1) value for the 7ΛLi(3/2+→1/2+) transition. Beyond E13, we plan to study impurity effects by observing possible changes in nuclear deformation caused by the presence of a Λ in sd-shell hypernuclei, as well as to investigate various heavier Λ hypernuclei in order to precisely determine the energies of Λ single-particle orbits.

Spectra of 1p-shell hypernuclei with ΛN and ΛNN interactions

Spectra of 1p-shell hypernuclei with ΛN and ΛNN interactions