Experiments for doubly strange hypernuclei with nuclear emulsion have been performed at KEK and J-PARC for the past 30 years. From detected 47 events, the characteristics were understood for Λ-Λ ...interaction to be weakly attractive, linear mass number dependence for two Λs binding energy, presence of Ξ hypernucleus, and it can be seen for something like the level structure of 15 Ξ C. Developing scanning method, so-called overall-scanning method , probably presents more rich information on not only doubly strange hypernuclei but also single-Λ hypernuclei.
The study on doubly-strange hypernuclei has been performed with nuclear emulsion detector at KEK-PS and J-PARC for 30 years. Detected 47 candidate events of doubly-strange hypernuclei show ...characteristics for the Λ-Λ and Ξ-
N
interactions. The Λ-Λ interaction is weakly at-tractive and the binding energy of two Λ hyperons to nuclei shows linear dependence on the mass number of a nucleus. The Ξ
–
hyperon is found to be bound by the
14
N nucleus, forming the
Ξ
15
C hypernucleus, with larger energy than that given by Coulomb force. Also, the level scheme of the Ξ
–
hyperon in the
Ξ
15
C hypernucleus can be seen. With the light source of hard X-ray instead of an optical microscope, since it will enable to count grains constituting tracks in the emulsion, charge recognitions of light nuclei, especially H
+
and He
2+
, can be possible. This would work effectively in determining the nuclides of doubly-strange hypernuclei. The
‘overall-scanning method’
to scan whole volume of the emulsion sheets will allow to detect nearly 1 x 10
3
events of doubly-strange hypernuclei, which is the expected number recorded in the emulsion of the E07 experiment, with machine learning in the near future.
The search for double hypernucleus (DH) with two units of Strangeness has now reached 46 sample events. The only one that has continued to detect DH in these 35 years is the experiment using nuclear ...emulsion as a detector. Regarding the double-Λ hypernucleus, which is a nucleus having two Λ particles, the energy that binds the two Λ particles to the nucleus seems to change linearly with the atomic-mass number. There seems to be a level structure for s- and p-state in the Ξ hypernucleus (15Ξ C), where the Ξ－ particle is deeply bound to 14N nucleus by the strong force beyond Coulomb force. In near future, we expect to obtain more detailed information on DH by introducing a machine-learning model to scan DH in whole area of the emulsion.
The knowledge of
interaction is quite limited. At present, only
Nagara
event gives a definite information for its interaction among nine samples of double hypernucleus in the world. To obtain nuclear ...mass dependence of the interaction with one thousand double hypernuclei, a system for fully automated scanning of
hyperons was developed by the success of precise position alignment (1 μm) of nuclear emulsion plates. Production and decay of double hypernuclei have typical topologies with three vertices. The development of a system to search for such topologies in overall emulsion is ongoing.
Abstract
We are developing the Gamma-Ray Astro-Imager with Nuclear Emulsion project, designed for 10 MeV–100 GeV cosmic
γ
-ray observations with a high angular resolution (5′/0.°08 at 1–2 GeV) and a ...polarization-sensitive large-aperture (∼10 m
2
) emulsion telescope for repeated long-duration balloon flights. In 2018, a balloon-borne experiment was carried out in Australia with a 0.38 m
2
sensitive area and a flight duration of 17.4 hr, including 6.7 hr of Vela observations. Significant improvements compared with the 2015 balloon-borne experiment were achieved by a factor of 5, including both an increase in effective area × time and a reduction in the background contribution. We aimed to demonstrate the telescope’s overall performance based on detection and imaging of a known
γ
-ray source, the Vela pulsar. A robust detection of the Vela pulsar was achieved with a 68% containment radius of 0.°42, at a significance of 6
σ
, at energies above 80 MeV. The resulting angular profile is consistent with that of a pointlike source. We achieved the current best imaging performance of the Vela pulsar using an emulsion
γ
-ray telescope with the highest angular resolution of any
γ
-ray telescope to date.
We review recent progress in
S
=−2 hypernuclei such as double-Λ hypernuclei and Ξ hypernuclei, which are composed of a nucleus and one or two hyperons, such as a Λ or a Ξ particle. Through ...observations of
He, such as the Nagara event, we obtain important information about the ΛΛ interaction. Using this information, we perform a four-body calculation of ααΛΛ for
Be, which was observed at KEK as the Demachi-Yanagi event. We interpret this event as the
excited state. We calculate energy levels of
Be within the framework of an αα
n
ΛΛ five-body cluster model, and then interpret the Hida event, which was observed at KEK as the ground state of
Be. Motivated by observation of the Kiso event of
C, by using the Skyrme-Hartree-Fock and relativistic mean-field frameworks, we calculate the energy spectra of this hypernucleus. We interpret this event as the
14
N(g.s.)+Ξ
−
(0
p
) state. Finally, we propose an experiment on
H and
Li to extract information about the spin- and isospin-averaged parts of the Ξ
N
interaction.
An automatic track following system has been successfully developed to follow tracks in nuclear emulsion sheets exposed with beam up to the limit to be observed for the first time. The track followed ...rate of the system is 99.5% with the assistance of the new techniques. The working speed for a track is less than 1min through one thick emulsion sheet, whereas it is 15 times faster than that of semiautomatic system with human. The system working for 24h is applied for the E07 experiment at J-PARC and makes it possible to detect ~102 nuclei with double strangeness (S=−2 nuclei) within one year. Regarding analyses to identify nuclear species of S=−2 nuclei, the system shows quite decent job for significant steps such as following tracks emitted to spherical directions from S=−2 nuclei, measurement of lengths of followed tracks, and so on.
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.
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