arXiv subjects

Masayoshi Shoji

Publications and source records attributed to Masayoshi Shoji.

10 recordsLinked to original sources

arXiv2026

Hit-rate capability of a silicon strip detector module for decay positron detection in the J-PARC muon $g-2$/EDM experiment

In the J-PARC muon $g-2$/EDM experiment, a silicon strip detector will be used to detect positrons from muon decays. The detector consists of planes of detector modules arranged radially. The expected maximum hit rate reaches 1.4~MHz per sensor strip, and achieving high detection efficiency even under such hit-rate conditions is a key performance requirement. We have developed the smallest unit of the detector module, and its performance was evaluated using a muon beam at the J-PARC MLF H-line. The specifications of the detector module and the evaluated hit-rate capability are described in this article.

physics.ins-det↗

arXiv2026

One-week optical observations of pulsed emission from the Crab pulsar with IMONY on the 3.8 m Seimei telescope

We report our optical observations of the Crab pulsar using the Imager of MPPC-based Optical photoN counter from Yamagata (IMONY), a high-time-resolution photon-counting imager with 100 ns timing resolution, mounted on the 3.8 m Seimei telescope in Japan (f/D~6). The detector format was upgraded from a $4\times4$ to an $8\times8$ GAPD array with larger pixels ($100$ to $200~{μm}$), resulting in a 14".5 field of view on the Seimei telescope. We conducted nightly optical observations for one week, including two nights of simultaneous optical and radio observations with the 64 m Usuda radio telescope. Thanks to the large diameter of the Seimei telescope and the high time resolution of IMONY, we successfully detected optical Single Pulses (SPs) emitted in each rotation. Moreover, we found an optical peak timing drift of $30\pm7.9~\mathrm{μs}$ over three days, with a significance of $3.9σ$. The corresponding emission region size is 9.1 km, which is equivalent to 0.006 times the light cylinder radius of the Crab pulsar. We ruled out the possibility of a pulsar glitch and suggested that the optical pulsed emission region of the Crab pulsar may fluctuate due to the spatial drift and variations in the magnetospheric caustics.

astro-ph.IM↗

arXiv2025

Calibrating the photometric performance of a high-time-resolution photon-counting imager for optical astronomy

Optical observations with high time resolution are essential for understanding the origin of sub-millisecond timescale astronomical phenomena, including giant radio pulses from the Crab Pulsar. We have developed a high-speed imaging system called the Imager of MPPC-based Optical photoN counter from Yamagata (IMONY). The system uses a customized Multi-Pixel Photon Counter (MPPC), which independently reads out signals from all $8\times8$ pixels and functions as an imager based on a Geiger-mode avalanche photodiode array. This system assigns timestamps to detected photons with a time resolution of 100 ns. We installed IMONY on the 3.8 m aperture Seimei Telescope in Okayama, Japan. We have successfully detected the 34-ms period of the Crab Pulsar and imaged stars in the sensor's field of view. However, we have also found that a small fraction of the pixels have shown double or multiple pulses that are used for photon arrival timing. This situation is likely due to circuit noise and may unfortunately result in overestimating the number of photons detected. In order to precisely estimate the photon flux of targets or the sky background, calibration of such over-counts is important. We measured the number of detected photons relative to the light intensity of each pixel in a laboratory environment. We estimated the number of spurious hit pulses caused by signal tail fluctuations exceeding the comparator threshold, based on the exponential distribution of time intervals between pulses. These are distinct from typical SiPM afterpulses and originate from electronic effects in our readout system. After applying the calibration to the observed data, we confirmed the linearity between the V-band magnitudes of stars and the number of detected photons.

astro-ph.IM↗

arXiv2025

Optical photon-counting observation of the Crab pulsar with Kanata telescope using prototype IMONY

We have developed an optical photon-counting imaging system, IMONY, as an instrument for short-scale time-domain astronomy. In this study, we utilized a Geiger avalanche photodiode array with a $4\times 4$ pixel configuration, with each pixel measuring \SI{100}{\micro m}. We developed a dedicated analog frontend board and constructed a data acquisition system with an FPGA to time-stamp each photon with a time resolution of \SI{100}{\ns}. We mounted a prototype model of the system on the 1.5-m Kanata telescope, intending to observe the Crab pulsar and conduct joint observations with Iitate and Usuda radio telescopes in Japan. We successfully demonstrated that IMONY could image the Crab pulsar as an expected point source and acquire the well-known pulse shape. We found that the time lag between the optical and radio main pulses was $304\pm$\SI{35}{μs}, consistent with previous studies.

astro-ph.IM↗

arXiv2024

The quality assurance test of the SliT ASIC for the J-PARC muon $g-2$/EDM experiment

The SliT ASIC is a readout chip for the silicon strip detector to be used at the J-PARC muon $g-2$/EDM experiment. The production version of SliT128D was designed and mass production was finished. A quality assurance test method for bare SliT128D chips was developed to provide a sufficient number of chips for the experiment. The quality assurance test of the SliT128D chips was performed and 5735 chips were inspected. No defect was observed in chips of 84.3%. Accepting a few channels with poor time walk performance out of 128 channels per chip, more than 90% yield can be achieved, which is sufficient to construct the whole detector.

physics.ins-det↗

arXiv2021

An FPGA-based Trigger System with Online Track Recognition in COMET Phase-I

An FPGA-based online trigger system has been developed for the COMET Phase-I experiment. This experiment searches for muon-to-electron conversion, which has never been observed yet. A drift chamber and trigger counters detect a mono-energetic electron from the conversion process in a 1-T solenoidal magnetic field. A highly intense muon source is applied to reach unprecedented experimental sensitivity. It also generates undesirable background particles, and a trigger rate due to these particles is expected to be much higher than an acceptable trigger rate in the data acquisition system. By using hit information from the drift chamber too, the online trigger system efficiently suppresses a background trigger rate while keeping signal-event acceptance large. A characteristic of this system is the utilization of the machine learning technique in the form of look-up tables on hardware. An initial simulation study indicates that the signal-event acceptance of the online trigger is 96% while the background trigger rate is reduced from over $90\,\mathrm{kHz}$ to $13\,\mathrm{kHz}$. For this scenario, we have produced trigger-related electronics that construct a distributed trigger architecture. The total latency of the trigger system was estimated to be $3.2\,\mathrm{μs}$, and the first operation test was carried out by using a part of the drift-chamber readout region.

physics.ins-det↗

arXiv2021

Performance of the Unified Readout System of Belle II

The Belle II experiment at the SuperKEKB collider at KEK, Tsukuba, Japan has successfully started taking data with the full detector in March 2019. Belle II is a luminosity frontier experiment of the new generation to search for physics beyond the Standard Model of elementary particles, from precision measurements of a huge number of B and charm mesons and tau leptons. In order to read out the events at a high rate from the seven subdetectors of Belle II, we adopt a highly unified readout system, including a unified trigger timing distribution system (TTD), a unified high speed data link system (Belle2link), and a common backend system to receive Belle2link data. Each subdetector frontend readout system has a field-programmable gate array (FPGA) in which unified firmware components of the TTD receiver and Belle2link transmitter are embedded. The system is designed for data taking at a trigger rate up to 30 kHz with a dead-time fraction of about 1% in the frontend readout system. The trigger rate is still much lower than our design. However, the background level is already high due to the initial vacuum condition and other accelerator parameters, and it is the most limiting factor of the accelerator and detector operation. Hence the occupancy and radiation effects to the frontend electronics are rather severe, and they cause various kind of instabilities. We present the performance of the system, including the achieved trigger rate, dead-time fraction, stability, and discuss the experience gained during the operation.

physics.ins-det↗

arXiv2020

SliT: A Strip-sensor Readout Chip with Subnanosecond Time-walk for the J-PARC Muon $g-2$/EDM Experiment

A new silicon-strip readout chip named "SliT" has been developed for the measurement of the muon anomalous magnetic moment and electric dipole moment at J-PARC. The SliT is designed in the Silterra 180 nm CMOS technology with mixed-signal integrated circuits. An analog circuit incorporates a conventional charge-sensitive amplifier, shaping amplifiers, and two distinct discriminators for each of 128 identical channels. A digital part includes storage memories, an event building block, a serializer, and LVDS drivers. A distinct feature of the SliT is utilization of the zero-cross architecture, which consists of a CR-RC filter followed by a CR circuit as a voltage differentiator. This architecture enables to generate hit signals with subnanosecond amplitude-independent time walk, which is the primary requirement for the experiment. The test results show the time walk of $0.38 \pm 0.16$ ns between 0.5 and 3 MIP signals. The equivalent noise charge is $1547 \pm 75 $ $e^{-}$ (rms) at $C_{\rm det} = 33$ pF as a strip-sensor capacitance. Other functionalities such as a strip-sensor readout chip have also been proven in the tests. The SliT128C satisfies all requirements of the J-PARC muon $g-2$/EDM experiment.

physics.ins-det↗

arXiv2019

Prototype Front-end ASIC for Silicon-strip Detectors of J-PARC Muon g-2/EDM Experiment

We report on the development of a front-end ASIC for silicon-strip detectors of the J-PARC Muon g-2/EDM experiment. This experiment aims to measure the muon anomalous magnetic moment and electric dipole moment precisely to explore new physics beyond the Standard Model. Since the time and momentum of positrons from muon decay are key information in the experiment, a fast response with high granularity is demanded to silicon-strip detectors as the positron tracker. The readout ASIC is thus required to tolerate a high hit rate of 1.4 MHz per strip and to have deep memory for the period of 40 us with 5 ns time resolution. To satisfy the experimental requirements, an analog prototype ASIC was newly designed with the Silterra 180 nm CMOS technology. In the evaluation test, the time-walk was demonstrated to reach 0.8~ns with a sufficient dynamic range of 6~MIPs and pulse width of 45~ns for 1 MIP event. The design details and performance of the ASIC are discussed in this article.

physics.ins-det↗

arXiv2019

Prototype Analog Front-end for Negative-ion Gas and Dual-phase Liquid-Ar TPCs

We report on the recent development of a versatile analog front-end compatible with a negative-ion $μ$-TPC for a directional dark matter search as well as a dual-phase, next-generation $\mathcal{O}$(10~kt) liquid argon TPC to study neutrino oscillations, nucleon decay, and astrophysical neutrinos. Although the operating conditions for negative-ion and liquid argon TPCs are quite different (room temperature \textit{vs.} $\sim$88~K operation, respectively), the readout electronics requirements are similar. Both require a wide-dynamic range up to 1600 fC, and less than 2000--5000 e$^-$ noise for a typical signal of 80 fC with a detector capacitance of $C_{\rm det} \approx 300$~pF. In order to fulfill such challenging requirements, a prototype ASIC was newly designed using 180-nm CMOS technology. Here, we report on the performance of this ASIC, including measurements of shaping time, dynamic range, and equivalent noise charge (ENC). We also demonstrate the first operation of this ASIC on a low-pressure negative-ion $μ$-TPC.

physics.ins-det↗