arXiv subjects

Atsushi Tokiyasu

Publications and source records attributed to Atsushi Tokiyasu.

5 recordsLinked to original sources

arXiv2026

Design and Performance of a Monolithic Plastic Scintillator Tracker with Embedded Scatterers

We propose a new scintillator-based tracker concept based on a monolithic plastic scintillator plate with embedded scatterers and wavelength-shifting fiber readout. The embedded scatterers localize scintillation light so that channels closer to the charged-particle crossing point collect more light. The particle crossing position is reconstructed from the channel-to-channel light yield distribution with a position resolution well below the readout pitch. We performed a positron beam test with prototypes to validate the reconstruction principle and to evaluate the detection efficiency and position resolution. The beam test validated the position reconstruction principle, and demonstrated a near-100% detection efficiency and a position resolution of 1.47 mm for normal incidence and 1.85 mm for an incidence angle of 45°, with a 10-mm readout pitch. In this paper, we describe the detector concept, the reconstruction method, and the results of the beam test.

physics.ins-det↗

arXiv2026

First observation of the $γ$-ray beam production by the backward Compton scattering of reflected synchrotron radiation in the extreme ultraviolet range

Compton scattering of photons off high-energy electrons is a fundamental quantum mechanical process widely utilized to produce a $γ$-ray beam for scientific research. Instead of injecting laser light into a storage ring as a conventional way, we have developed an innovative method to achieve drastically higher energies approaching the ring energy by the backward Compton scattering of extreme ultraviolet (EUV) light. In this method, $92$ $\mathrm{eV}$ photons obtained from an undulator in a storage ring were reflected back to the original ring using a Mo/Si multilayer mirror. Consequently, $γ$-ray beam production through the EUV light Compton scattering using reflected synchrotron radiation was observed for the first time in a demonstration experiment conducted at the $1$ $\mathrm{GeV}$ ring, NewSUBARU. The measured energy spectrum was well reproduced by a theoretical calculation with the maximum energy of $0.543$ $\mathrm{GeV}$. The production rate was $1.4 \pm 0.1$ kcps for the energies above $0.160$ $\mathrm{GeV}$. This rate was quantitatively explained by the luminosity and the scattering cross section. The present work paved the way to create a new $γ$-ray beam source for future applications such as hadron photoproduction experiments.

physics.acc-ph↗

arXiv2025

Development and performance evaluation of a water-based liquid scintillator tracking detector with wavelength-shifting fiber readout

We have developed a novel tracking detector utilizing a water-based liquid scintillator (WbLS) for the accurate characterization of neutrino interactions on a water target. In this detector, the WbLS is optically segmented into small cells by reflective separators, and the scintillation light is read out in three directions using wavelength-shifting fibers coupled to silicon photomultipliers. We developed and optimized WbLS samples for this application and measured their light yield using cosmic-ray muons. Subsequently, we constructed a prototype of the WbLS tracking detector and evaluated its performance with a positron beam. The beam test demonstrated good tracking performance, although the light yield was lower than required. The result prompted a review of the surfactant used in the WbLS and the material of the optical separators, leading to a significant improvement in light yield. In this paper, we report on a design of the WbLS tracking detector, the development of the WbLS, the results of the beam test, and subsequent improvements to the WbLS and optical separators.

physics.ins-det↗

arXiv2025

Performance evaluation of electron multiplier tubes as a high-intensity muon beam monitor of accelerator neutrino experiments

Upgrade work towards increasing the beam intensity of the neutrino beamline at J- PARC is underway. Monitoring tertiary muon beams is essential for stable operation of the beamline. Accordingly, we plan to replace the present muon monitor sensors with electron multiplier tubes (EMTs). We investigated the radiation tolerance and linearity response of EMTs using a 90 MeV electron beam. An EMTs was irradiated with electrons up to 470 nC. EMTs show higher radiation tolerance than the Si sensors which are presently used as one of the muon monitor detectors for the T2K long-baseline neutrino experiment at J-PARC. The integrated charge yield decrease is found to be less than 8% after a beam irradiation equivalent to 132 days of operation at the future J-PARC beam power of 1.3 MW. The EMTs show linearity better than $\pm$5% up to the future beam intensity. The observed yield decrease is likely due to dynode deterioration based on the detailed investigation. The studies described here confirm that EMTs can be used as a high-intensity muon beam monitor. From the reported results, we are proceeding with the installation in the J-PARC neutrino beamline.

physics.ins-det↗

arXiv2014

Observation of the "$K^-pp$"-like structure in the $d(π^+, K^+)$ reaction at 1.69 GeV/$c$

We have observed a "$K^-pp$"-like structure in the $d(π^+,K^+)$ reaction at 1.69 GeV/$c$. In this reaction $Λ(1405)$ hyperon resonance is expected to be produced as a doorway to form the $K^-pp$ through the $Λ^*p\rightarrow K^-pp$ process. However, most of the produced $Λ(1405)$'s would escape from deuteron without secondary reactions. Therefore, coincidence of high-momentum ($>$ 250~MeV/$c$) proton(s) in large emission angles ($39^\circ<θ_{lab.}<122^\circ$) was requested to enhance the signal-to-background ratio. A broad enhancement in the proton coincidence spectra are observed around the missing-mass of 2.27 GeV/$c^2$, which corresponds to the $K^-pp$ binding energy of 95 $^{+18}_{-17}$ (stat.) $^{+30}_{-21}$ (syst.) MeV and the width of 162 $^{+87}_{-45}$ (stat.) $^{+66}_{-78}$ (syst.) MeV.

nucl-ex↗