Observation of Spin-Dependent Charge Symmetry Breaking in ΛN Interaction: Gamma-Ray Spectroscopy of _{Λ}^{4}He

High accuracy spectroscopy of 3- and 4-body Λ hypernuclei at Jefferson Lab

JLab E12-19-002 Experiment is planned to measure the Λ-binding energies of 3ΛH [Jπ = 1/2+ or 3/2+(T = 0)] and 4ΛH (1+) at JLab Hall C. The expected accuracy for the binding-energy measurement is |ΔBtotal Λ | ≃ 70 keV. The accurate spectroscopy for these light hypernuclei would shed light on the puzzle of the small binding energy and short lifetime of 3ΛH, and the chargesymmetry breaking in the ΛN interaction. We aim to perform the experiment in 2025.

Hypernuclear gamma-ray spectroscopy: summary and future prospect

The present status and prospects of hypernuclear γ-ray spectroscopy are summarized. In particular, 4-body hypernuclear γ-ray spectroscopy, the recent result of 4ΛHe and the future plan of 4ΛH and charge symmetry breaking in the ΛN interaction are presented. In addition, future plans to measure the Λ-spin-flip B(M1) values of 7Λ(3/2+ → 1/2+) and 12ΛC(2− → 1−) transitions are introduced. They aim to study the g-factor of Λ in the nuclear medium.

Study of Λn FSI with Λ quasi-free productions on the 3H(e, e′K+)X reaction at JLab

Abstract. An nnΛ is a neutral baryon system with no charge. The study of the pure Λ-neutron system such as nnΛ gives us information on the Λn interaction. The nnΛ search experiment (E12-17-003) was performed at JLab Hall A in 2018. In this article, the Λn FSI was investigated by a shape analysis of the 3H(e, e′K+)X missing mass spectrum, and a preliminary result for the Λn FSI study is given.

Status of the hyperon-nucleon interaction in chiral effective field theory

The Jülich-Bonn group aims at an extensive study of the baryonbaryon (BB) interaction involving strange baryons (Λ, Σ, Ξ) within SU(3) chiral effective field theory. An overview of achievements and new developments over the past few years is provided. The topics covered are: 1) Derivation of the leading charge-symmetry breaking (CSB) interaction for the ΛN system and its application in a study of CSB effects in A=4 Λ-hypernuclei. 2) Updated results for the ΞN interaction at NLO and predictions for Ξ−p correlation functions. 3) Extension of the ΛN-ΣN interaction to next-to-next-to-leading order.

Unique approach for precise determination of binding energies of hypernuclei with nuclear emulsion and machine learning

Hypertriton is the lightest hypernucleus and a benchmark in hypernuclear physics. However, it has recently been suggested that its lifetime and binding energy values may differ from the established values. To solve this puzzle, it is necessary to measure both values with a higher precision. For the precise measurement of the binding energy, we are aiming at developing a novel technique to measure the hypertriton binding energy with unprecedented accuracy by combining nuclear emulsion data and machine learning techniques. The analysis will be based on the J-PARC E07 nuclear emulsion data. Furthermore, a machine-learning model is being developed to identify other single and double-strangeness hypernuclei.

Study of charge symmetry breaking in A = 4 hypernuclei in √sNN = 3 GeV Au+Au collisions at RHIC

In these proceedings, we present the measurement of the charge symmetry breaking in A = 4 hypernuclei in Au+Au collisions at √sNN = 3 GeV. The signal reconstruction and binding energy measurements of 4ΛH and 4ΛHe, including corrections on momentum, are discussed. Our result of Λ binding energy difference for ground states is ΔBΛ(0+) = 0.16 ± 0.14(stat.) ± 0.10(syst.) MeV. Combined with the energy levels of excited states, the difference for excited states is ΔBΛ(1+) = −0.16 ± 0.14(stat.) ± 0.10(syst.) MeV which shows a negative sign with a magnitude comparable to the result of ground states. These results are compared with previous measurements and theoretical model calculations.

Baryonic effective field theory for light hypernuclei

Light hypernuclei containing one or two Λ baryons are the subject of an ongoing experimental campaign aiming to study the spectrum of these systems, as well as the 2 and 3-body interaction between Λ hyperons and nucleons. Here we shortly review the theoretical study of these systems within the framework of baryonic effective field theory.

Development of a triple coincidence method of reaction, gamma-ray, and weak decay in the hypernuclear gamma-ray spectroscopy at J-PARC

To understand the mechanism of the charge symmetry breaking between 4ΛH and 4ΛHe, we plan to measure the gamma-transition energy of 4ΛH (1+ → 0+) with a Ge detector array. For identification of the hypernucleus, we will perform triple coincidence with the reaction, γ-ray, and weak decay for the first time. We measure the pion from weak decay with a range counter. This method will enable γ-ray spectroscopy of various hyperfragments which cannot be directly produced by (K−, π−) or (π+, K+) reactions.

Resolving the Λ Hypernuclear Overbinding Problem in Pionless Effective Field Theory

We address the Λ hypernuclear "overbinding problem" in light hypernuclei which stands for a 1-3 MeV excessive Λ separation energy calculated in _{Λ}^{5}He. This problem arises in most few-body calculations that reproduce ground-state Λ separation energies in the lighter Λ hypernuclei within various hyperon-nucleon interaction models. Recent pionless effective field theory (πEFT) nuclear few-body calculations are extended in this work to Λ hypernuclei. At leading order, the ΛN low-energy constants are associated with ΛN scattering lengths, and the ΛNN low-energy constants are fitted to Λ separation energies (B_{Λ}^{exp}) for A≤4. The resulting πEFT interaction reproduces in few-body stochastic variational method calculations the reported value B_{Λ}^{exp}(_{Λ}^{5}He)=3.12±0.02  MeV within a fraction of MeV over a broad range of πEFT cutoff parameters. Possible consequences and extensions to heavier hypernuclei and to neutron-star matter are discussed.

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.

Induced Hyperon-Nucleon-Nucleon Interactions and the Hyperon Puzzle

We present the first ab initio calculations for p-shell hypernuclei including hyperon-nucleon-nucleon (YNN) contributions induced by a similarity renormalization group transformation of the initial hyperon-nucleon interaction. The transformation including the YNN terms conserves the spectrum of the Hamiltonian while drastically improving model-space convergence of the importance-truncated no-core model, allowing a precise extraction of binding and excitation energies. Results using a hyperon-nucleon interaction at leading order in chiral effective field theory for lower- to mid-p-shell hypernuclei show a good reproduction of experimental excitation energies while hyperon separation energies are typically overestimated. The induced YNN contributions are strongly repulsive and we show that they are related to a decoupling of the Σ hyperons from the hypernuclear system, i.e., a suppression of the Λ-Σ conversion terms in the Hamiltonian. This is linked to the so-called hyperon puzzle in neutron-star physics and provides a basic mechanism for the explanation of strong ΛNN three-baryon forces.

Ab initio Calculations of Charge Symmetry Breaking in the A=4 Hypernuclei

We report on ab initio no-core shell model calculations of the mirror Λ hypernuclei _{Λ}^{4}H and _{Λ}^{4}He, using the Bonn-Jülich leading-order chiral effective field theory hyperon-nucleon potentials plus a charge symmetry breaking Λ-Σ^{0} 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 charge symmetry breaking 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 recent measurements of the _{Λ}^{4}H(0_{g.s.}^{+}) binding energy at the Mainz Microtron [A. Esser et al. (A1 Collaboration), Phys. Rev. Lett. 114, 232501 (2015)] and the _{Λ}^{4}He(1_{exc}^{+}) excitation energy [T.O. Yamamoto et al. (J-PARC E13 Collaboration), Phys. Rev. Lett. 115, 222501 (2015)].