Alpha-decay events in a nuclear emulsion are standard calibration sources for the relation between the track length and the kinetic energy in each emulsion sheet. We developed an efficient classifier ...that sorts such alpha-decay events from various vertex-like objects in an emulsion using a convolutional neural network (CNN). We trained the CNN using 15885 images of vertex-like objects, including 906 alpha-decay events, and tested it using a dataset of 46948 images including 255 alpha-decay events. The precision and recall scores of the classification using the previous method without a CNN for the same dataset were 0.081 ± 0.006 and 0.788 ± 0.056, respectively. In contrast, our trained models achieved an average precision score of 0.760 ± 0.006 for the test dataset, after extensively tuning the hyperparameters of the CNN. Moreover, for the model obtained, the discrimination threshold of the classification can be adjusted arbitrarily according to the trade-off between the precision and recall scores. Furthermore, the developed classifier obtained a precision of 0.571 ± 0.017 when the recall score was assigned a value of 0.788. Finally, the developed CNN method reduced the need for additional human visual inspection, required after classification, by a factor of approximately 1/7, compared to the former method without a CNN, proving the feasibility of the proposed classifier.
We revisit previous measurements for the hypertriton binding energy with nuclear emulsion which were published in 1968 and 1973. Using Monte Carlo simulations, the systematic error of the hypertriton ...binding energy in emulsion measurements has been estimated to be approximately 28 keV. We corroborate the recent works that re-evaluate the hypertriton binding energy by using the former emulsion measurements in the present work, and the ambiguities and difficulties of the reevaluation are observed. Considering the need of new precise measurements with a well-controlled systematic error, we introduce a new approach by analyzing the existing nuclear emulsion data from the J-PARC E07 experiment, from which the binding energy of hypertriton could be determined, with both statistical and systematic errors, to be approximately 30 keV with 400 events.
We have developed a gas electron multiplier (GEM)-based time projection chamber (TPC) for the H-dibaryon search experiment at J-PARC. High-rate K− beam particles enter a TPC gas volume of ...approximately 0.2 m3, in a direction perpendicular to the electric field. A long-rectangular hollow section is located inside the TPC volume to accommodate a diamond target. We commissioned the TPC using 230-MeV protons with beam rates of up to 1 MHz. The TPC data acquisition system collected 5768 pad signals in full readout mode, with almost 100% efficiency, at a preset trigger rate of 230 Hz. We operated the TPC in an Ar/CH4 gas mixture (90/10) without a magnetic field. The spatial resolutions on the pad plane are measured to be 400–700μm, which correspond to 230–300μm in a magnetic field of 1 T. We confirmed high tracking capability at beam rates of up to 1 MHz.
Ξ
−
atomic X-ray spectroscopy is one of the most useful methods for investigation of the Ξ-nucleus strong interaction. A serious problem in the measurement is the significant background coming from ...in-flight Ξ
−
decay. For the first Ξ
−
atomic X-ray spectroscopy experiment, a novel method of identifying stopped Ξ
−
events using nuclear emulsion was developed to reject background photons from in-flight Ξ
−
decay. We succeeded in reducing the background to 1/170 by this method employing coincidence measurements using the nuclear emulsion and X-ray detectors.
A high statistics ∑p scattering experiment has been performed at the K1.8 beamline in the J-PARC Hadron Experimental Facility. Data for momentum-tagged ∑− beam running in a liquid hydrogen target ...were accumulated by detecting the π−p→K+∑− reaction with a high intensity π− beam of 20 M/spill. The number of the Σ− beam was about 1.7 × 107 in total. The ∑−ρ elastic scattering and the ∑−p → Λn inelastic scattering events were successfully observed with about 100 times larger statistics than that in past experiments.
Abstract
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, ΔE, 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.
The current understanding of light hypernuclei, which are sub-atomic nuclei with strangeness, is being challenged and studied in detail by several European research groups and collaborations. In ...recent years, studies of hypernuclei using high-energy heavy ion beams have reported unexpected results on the three-body hypernuclear state
3
Λ
H, named the hypertriton. For some time, reports of a shorter lifetime and larger binding energy than what was previously accepted have created a puzzling situation for its theoretical description; this is known as the "hypertriton puzzle". With the inclusion of the most recent experimental measurements, the current status of the hypertriton puzzle is evolving. Additionally, the possible neutral bound state of a Λ hyperon with two neutrons, nnΛ, has raised questions about our understanding of the formation of light hypernuclei either in bound or resonance states. These results have initiated several ongoing experimental programs all over the world to study these three-body hypernuclear states precisely. We are studying these light hypernuclear states by employing heavy ion beams at 2
A
GeV on a fixed carbon target with the WASA detector system and the Fragment Separator (FRS) at GSI. The WASA-FRS experimental campaign was performed during the first quarter of 2022, and this paper presents a short overview of the campaign and how it seeks to tackle the hypertriton and nnΛ puzzles. Data analysis is ongoing, and several preliminary results will be reported.
An experiment was performed at GSI with the objective of measuring theβ-intensity distribution in the decay of Hg, Au and Pt isotopes around N=126 using the total absorption gamma-ray spectroscopy ...technique. The aim is to benchmark theoretical models used to make predictions of half-life and neutron emission probabilities of exotic nuclei involved in the rapid neutron capture process, leading to the synthesis of very heavy elements. This paper presents some experimental details and the current status of the analysis.
We have developed a time-of-flight (ToF) array consisting of 24 plastic scintillators for triggering and timing measurements in a series of planned experiments to study double-strangeness hadronic ...and nuclear systems at the K1.8 beamline of J-PARC. Each ToF scintillator is 180cm long with a cross-section of 8×3cm2, and is read out by H1949-50 photomultiplier tubes at both ends. The timing and attenuation properties of the scintillators are measured using cosmic-ray muons and β rays from 90Sr. The cosmic-ray muon events are triggered by three pairs of 120-cm-long plastic scintillators, sandwiching the ToF array. The intrinsic time resolutions of the scintillators are estimated to be in the range 60–100ps, which is adequate for reliable separation between π and K at 1.2GeV/c. The attenuation length is measured to be approximately 210cm, which is half that for a bulk scintillator.
A new hyperon-proton scattering experiment, dubbed J-PARC E40, was performed to measure differential cross sections of the Σ
+
p
, Σ
−
p
elastic scatterings and the Σ
−
p
→ Λ
n
scattering by ...identifying a lot of Σ particles in the momentum ranging from 0.4 to 0.8 GeV/
c
produced by the
π
±
p
→
K
+
Σ
±
reactions. We successfully measured the differential cross sections of these three channels with a drastically improved accuracy with a fine angular step. These new data will become important experimental constraints to improve the theories of the two-body baryon-baryon interactions. Following this success, we proposed a new experiment to measure the differential cross sections and spin observables by using a highly polarized Λ beam for providing quantitative information on the Λ
N
interaction. The results of three Σ
p
channels and future prospects of the Λ
p
scattering experiment are described.
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