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The WASA-FRS experiment aims to reveal the nature of light Λ hypernuclei with heavy-ion beams. The lifetimes of hypernuclei are measured precisely from their decay lengths and kinematics. To reconstruct a π - track emitted from hypernuclear decay, track finding is an important issue. In this study, a machine learning analysis method with a graph neural network (GNN), which is a powerful tool for deducing the connection between data nodes, was developed to obtain track associations from numerous combinations of hit information provided in detectors based on a Monte Carlo simulation. An efficiency of 98% was achieved for tracking π - mesons using the developed GNN model. The GNN model can also estimate the charge and momentum of the particles of interest. More than 99.9% of the negative charged particles were correctly identified with a momentum accuracy of 6.3%. [ABSTRACT FROM AUTHOR]

Ξ− atomic X-ray spectroscopy is one of the most useful methods for investigation of the Ξ–nucleus strong interaction. Since the X-ray energy is shifted and/or broadened due to the Ξ–nucleus strong interaction compared to those calculated from electromagnetic interaction alone, the measurement of the energy shift, Δ E , and the width, Γ, give us information on the Ξ–nucleus potential. A serious problem in the measurement is the significant background derived from in-flight Ξ− decay. A novel method of identifying stopped Ξ− events using the nuclear emulsion was developed to realize the first Ξ− atomic X-ray spectroscopy experiment as the J-PARC E07 experiment, which also aimed at searching for ΛΛ and Ξ− hypernuclei in the emulsion. The X-rays emitted from Ξ− Br and Ξ− Ag atoms were measured using germanium detectors. No clear peaks were observed in the obtained spectra. However, we succeeded in reducing the background to 1/170 by this method employing coincidence measurements using nuclear emulsion and X-ray detectors. [ABSTRACT FROM AUTHOR]

Bound systems of |$\Xi^-$| – |$^{14}_{}{\rm N}$| are studied via |$\Xi^-$| capture at rest followed by emission of a twin single- |$\Lambda$| hypernucleus in the emulsion detectors. Two events forming extremely deep |$\Xi^-$| bound states were obtained by analysis of a hybrid method in the E07 experiment at J-PARC and reanalysis of the E373 experiment at KEK-PS. The decay mode of one event was assigned as |$\Xi^-+^{14}\!\,\!\!{\rm N}\to^{5}_{\Lambda}\!\!\!{\rm He} + ^{5}_{\Lambda}\!\!{\rm He} + ^{4}\!\!{\rm He} + \mathrm{n}$|⁠. Since there are no excited states for daughter particles, the binding energy of the |$\Xi^-$| hyperon, |$B_{\Xi^-}$|⁠ , in the |$^{14}_{}{\rm N}$| nucleus was uniquely determined to be |$6.27 \pm 0.27$| MeV. Another |$\Xi^-$| – |$^{14}_{}{\rm N}$| system via the decay |$^{9}_{\Lambda}{\rm Be} + ^{5}_{\Lambda}\!\!\!{\rm He} + \mathrm{n}$| brings a |$B_{\Xi^-}$| value, |$8.00 \pm 0.77$| MeV or |$4.96 \pm 0.77$| MeV, where the two possible values of |$B_{\Xi^-}$| correspond to the ground and the excited states of the daughter |$^{9}_{\Lambda}{\rm Be}$| nucleus, respectively. Because the |$B_{\Xi^-}$| values are larger than those of the previously reported events (KISO and IBUKI), which are both interpreted as the nuclear |$1p$| state of the |$\Xi^-$| – |$^{14}_{}{\rm N}$| system, these new events give the first indication of the nuclear |$1s$| state of the |$\Xi$| hypernucleus, |$^{15}_{\Xi}{\rm C}$|⁠. [ABSTRACT FROM AUTHOR]

A double- |$\Lambda$| hypernucleus, |${}_{\Lambda\Lambda}\mathrm{Be}$|⁠, was observed by the J-PARC E07 Collaboration in nuclear emulsions tagged by the (⁠|$K^{-}, K^{+}$|⁠) reaction. This event was interpreted as the production and decay of |$ {}_{\Lambda\Lambda}^{\;10}\mathrm{Be}$|⁠, |${}_{\Lambda\Lambda}^{\;11}\mathrm{Be}$|⁠, or |${}_{\Lambda\Lambda}^{\;12}\mathrm{Be}^{*}$| via |$\Xi^{-}$| capture in |${}^{16}\mathrm{O}$|⁠. By assuming capture in the atomic 3D state, the binding energies of two |$\Lambda$| hyperons (⁠|$B_{\Lambda\Lambda}$|⁠) of these double- |$\Lambda$| hypernuclei are obtained to be |$15.05 \pm 0.11\,\mathrm{MeV}$|⁠, |$19.07 \pm 0.11\,\mathrm{MeV}$|⁠, and |$13.68 \pm 0.11\,\mathrm{MeV}$|⁠, respectively. Based on the kinematic fitting, |${}_{\Lambda\Lambda}^{\;11}\mathrm{Be}$| is the most likely explanation for the observed event. [ABSTRACT FROM AUTHOR]

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 Λ nn 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, Δ p / p , of 5 × 1 0 − 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. [ABSTRACT FROM AUTHOR]

The hypernuclei, which are nuclei that contain the quark s , have been studied for more than 50 years. Notwithstanding, the recent experiments using high-energy heavy-ion induced reactions have challenged their current understanding. The high multiplicity of particles generated in the reaction allows for the measurement of the interaction point of the primary beam with the target. Then, a micro-vertex detection system for the WASA-FRS Experiments has been developed. Several experimental tests have been performed with 90Sr and 207Bi β sources and a 10-MeV proton beam at the CMAM tandem accelerator, and their results are reported. [ABSTRACT FROM AUTHOR]