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土屋 晴文; 榎戸 輝揚*; 和田 有希*; 古田 禄大; 中澤 知洋*; 湯浅 孝行*; 楳本 大悟*; 牧島 一夫*; GROWTH Collaboration*
Proceedings of Science (Internet), 358, p.1163_1 - 1163_6, 2021/07
Since 2006, the GROWTH experiment has been successfully operating at the coastal area of Japan Sea. The GROWTH experiment aims at elucidating how particles in lightning and thunderclouds are accelerated to relativistic energies to produce gamma rays and occasionally neutrons. According to observations done by the GROWTH experiment, it is found that there are two types of radiation bursts associated with winter thunderstorms. One is long bursts lasting for a few tens of seconds to a few minutes, being not clearly related to lightning. The other is short bursts in association with lightning. To better understand the production mechanism of these radiation bursts, we have developed a small-type of radiation detectors and increased observational points with the new detectors. In this presentation, we show an overview of observations done by the GROWTH experiment. Then we focus on recent several findings observed by the new detectors. One, which is categorized into long bursts, implies a relationship between a long burst and an intra/inter-cloud discharge. Another is a combination of short bursts and long ones, showing simultaneous detections of prompt gamma rays extending up to 10 MeV and the 511-keV annihilation ones. These gamma-ray signals demonstrate the occurrence of photonuclear reactions in lightning. Based on these results, we discuss the production mechanism of gamma rays related to thunderstorms.
佐藤 健太*; 谷田 聖; 他19名*
Proceedings of Science (Internet), 358, p.413_1 - 413_8, 2021/07
The Relativistic Heavy Ion Collider forward (RHICf) experiment aims at understanding the high-energy hadronic interaction by measuring the cross sections of very forward neutral particles in proton-proton collisions at = 510 GeV. For the analysis of the photon measurement, the trigger efficiency and the particle identification performance are studied by using the Monte Carlo simulation data and the experimental data. In the RHICf operation, two kinds of trigger modes (Shower, HighEM) were implemented. The trigger efficiency of the Shower trigger is 100% for photons with the energies more than 20 GeV. The HighEM trigger is designed to detect high energy photons effectively, and the trigger efficiency of the HighEM trigger is 90% for photons with the energies more than 130 GeV. The correction factor for the photon identification is calculated by using the efficiency and purity. It is found that this correction does not make a sizeable effect on the shape of the energy spectrum because the energy dependency of the factor is small.