Session 2WF: Exotic Hadrons and Strangeness Nuclear Physics across the Date Line II

Beam energy dependence of hypertriton production and lifetime measurement at RHIC

We will show the recent progress on hypertriton measurement in high energy heavy-ion collisions at RHIC. We will focus on the hypertriton and anti-hypertriton invariant yield measurements in Au$+$Au collisions at center of mass energy of 7.7, 11.5, 19.6, 27, 39 and 200 GeV. The updated hypertriton lifetime with larger statistics will be presented. The physics implication of the new data will be discussed.   

Study Light $\Lambda$ Hypernuclei From Decay Pion Spectroscopy

Continued primary electron beam with high intensity and precision, such that at JLab and MAMI, makes it possible to study light $\Lambda$ hypernuclei via the pion momentum spectroscopy from 2-body mesonic decay. The $\Lambda$ binding energy B$_{\Lambda}$ of ground state from various light hypernuclei (produced by fragmentations of the primary hypernuclei) can be simultaneously measured with unprecedented precision. The precisely measured B$_{\Lambda}$ from a sequence of light hypernuclei can solidly confirm some of the emulsion results which were measured unambiguously and replace those which were highly questionable from the emulsion technique, thus provide stringent information for theoretical investigation on the $\Lambda $N interactions. The precisely measured B$_{\Lambda}$ difference between the isospin mirror pairs of light hypernuclei may provide more reliable result in study the origin of the excessive charge symmetry breaking (CSB) in $\Lambda $N interactions. Through fragmentation, highly neutron rich light hypernuclei may have higher production rate than that from direction beam production. This makes it possible to search for hypernuclei with extreme neutron number, such as $^{6}_{\Lambda}$H or even $^{8}_{\Lambda}$H at the drip line. Therefore, the new technique with decay pion spectroscopy is highly promising and such experiment is already undergoing at MAMI. Part of the preliminary results from the MAMI experiment will be presented as illustration.   

Neutron-rich Lambda Hypernuclei

The J-PARC E10 experiment aims to produce $\Lambda$ hypernuclei close to the neutron drip-line to investigate hyperon-nucleon interactions in the asymmetric nuclear medium. Although the $\Lambda$ hyperon has an isospin $I$=0, a dependence of the $\Lambda N$ interaction on the overall isospin of $\Lambda$ hypernuclei may arise due to a coupling to $\Sigma$($I$=1) channel known as the ``$\Lambda N$-$\Sigma N$ mixing'' and may be investigated in structures of the neutron-rich $\Lambda$ hypernuclei. The structure of a highly neutron-rich hypernucleus, $^6_\Lambda{\rm H}$, is discussed theoretically quite extensively in connection with the contribution of the $\Lambda N$-$\Sigma N$ mixing to the binding. One of promising methods to produce the neutron-rich $\Lambda$ hypernuclei is the application of the double charge-exchange (DCX) reactions, such as the $(K^-,\pi^+)$ and the $(\pi^-,K^+)$ reactions. Recently, we carried out the first phase of the J-PARC E10 experiment to search for $^6_\Lambda{\rm H}$ by utilizing the $^6{\rm Li}(\pi^-,K^+)$ reaction. The experiment was designed to have a high sensitivity to search for the neutron-rich $\Lambda$ hypernuclei with high-resolution magnetic spectrometers and high-intensity pion beams available at the K1.8 beam line of the J-PARC 50 GeV Proton-Synchrotron facility. The yield of the reaction was extremely smaller than that in the $^{10}{\rm B}(\pi^-,K^+)^{10}_{~\Lambda}{\rm Li}$ reaction obtained in the previous KEK-E521 experiment at KEK-PS. A comparison will be made with the result of the measurement of the $^6{\rm Li}(K^-_{\rm stopped},\pi^+)$ reaction to search for $^6_\Lambda{\rm H}$ reported by the FINUDA experiment at DA$\Phi$NE.   

Shell-model aspects of the p-shell hypernuclei

Calculations using $p^ns_Y$ and $p^np_Y$ bases (Y = $\Lambda$ and $\Sigma$) have been quite successful in explaining data, $\gamma-$ray data in particular, for p-shell hypernuclei. The $p^np_Y$ basis, however, needs to be augmented by states with an $s_Y$ coupled to $1\hbar\omega$ states of the nuclear core, with the elimination of spurious center-of-mass states, to make a complete $1\hbar\omega$ hypernuclear basis. I hope to be able to show the results from such calculations which are necessary to describe the particle decay of directly produced hypernuclear states and the structure of low-energy states of non-normal parity.   

Structure of Lambda Hypernuclei with Antisymmetrized Molecular Dynamics

In this talk, we will discuss the structure change caused by a $\Lambda $ particle and structure of neutron-rich (n-rich) and \textit{sd} shell $\Lambda $ hypernuclei based on the antisymmetrized molecular dynamics (AMD). One of the unique and interesting aspects of hypernuclei is structure change caused by a hyperon(s) as an impurity in nuclei. In light $\Lambda $ hypernuclei, experimental and theoretical studies have revealed a couple of interesting structure changes such as shrinkage of the inter-cluster distance. In n-rich and \textit{sd} shell $\Lambda $ hypernuclei, it is expected that the variety of structure and structure changes will appear in the low energy regions, because n-rich and \textit{sd} shell nuclei have various structures. For example, the n-rich nucleus $^{11}$Be has the parity-inverted ground-state 1/2$^{+}$, which is inconsistent with the ordinary shell model picture. In \textit{sd} shell nuclei, it has been discussed that various deformations appear in the ground and low-lying states. For example, $^{24}$Mg is a candidate of triaxially deformed nuclei with the presence of the low-lying 2nd 2$^{+}$ state. To reveal the structure of the corresponding $\Lambda $ hypernuclei, we have extended the AMD model for hypernuclei (HyperAMD) and applied it to n-rich and \textit{sd} shell $\Lambda $ hypernuclei. The AMD model can describe various nuclear structures without assumptions on clustering and symmetry of nuclear deformations. Combined with the generator coordinate method (GCM), the HyperAMD model succeeded to describe the low-lying structure of \textit{p-sd} shell $\Lambda $ hypernuclei. In this study, we investigate several n-rich and \textit{sd} shell $\Lambda $ hypernuclei such as $^{12}_{\Lambda}$Be and $^{25}_{\Lambda}$Mg. In this talk, we will discuss the changes of the parity-inverted ground state of $^{11}$Be by adding a $\Lambda $ particle. Furthermore, in $^{25}_{\Lambda}$Mg, we will discuss a possibility to identify the nuclear (triaxial) deformation of Mg by using $\Lambda $ as a probe.   

Double Lambda and Xi hypernuclei

Nuclei with double strangeness (S $=$ -2) provide the key information to understand Baryon-Baryon interaction under the SU(3)$_f$ symmetry. Therefore we have carried out the experiments at KEK for quarter a century. Recently, the interaction in S $=$ -2 sector is noted to derive the information of the EOS of neutron star. The Lambda-Lambda interaction has been presented to be weak attractive by NAGARA event which showed the production and decay of 6He double-hypernucleus. The event also presented the lower mass limit of H dibaryon. In other five events, we obtained the knowledge about an excitation level of 10Be double-hypernucleus under the consistency with NAGARA event. Moreover, very recently, we have discovered a Xi-14N system which was deeply bound far from the atomic 3D level (0.17 MeV) for a captured Xi hyperon. Since a 8Li nucleus was associated with the decay of one of twin-hypernuclei, the event was uniquely identified as Xi- $+$ 14N $\Rightarrow$ 10Be$_L$ $+$ 5He$_L$. The system was selected from 8 million pictures on the test running for development of ``Overall Scanning'' to be used in the coming experiment. This is the first evidence of Xi hypernucleus to be bound and it is impacting for the study of Xi-N interaction. At J-PARC facility, for the further study of hyperon-hyperon interaction, we plan to perform the E07 experiment at J-PARC. In the workshop, we will review the above knowledge obtained by the experiments at KEK-PS, and discuss developed technologies to detected 10$^2$ or more double-hypernuclei in the E07 experiment at J-PARC.