Development of Time-of-flight Detecter for Gravitational Constant of Antihydrogen in GBAR Experiment

Abstract

One of the first endeavor to directly examine the gravitational property of antimatter, the GBAR(Gravitational Behavior of Antihydrogen at Rest) experiment aims to observe the free-fall of antihydrogen. When laser detaches an excess positron from an ultra cold antihydrogen ion, the resulting antihydrogen escapes from a Paul trap and undergoes free-fall. To measure its gravitational constant, we need to detect the free-fall time and annihilation position of the antihydrogen. This article describes the development of the Time-Of-Flight(TOF) detector and its performance. The detector, which is an array of plastic scintillation counters covering the free-fall chamber(FFC), is required to have a time resolution better than 200 ps to reject cosmic rays, the most significant sources of background noise. During the summer in 2017, a wall of the TOF was installed at the Antiproton Decelerator(AD) hall, CERN and a set of the cosmic ray tests were conducted. As a result, we confirmed that the average time resolution of each counter is 76 ps, and the position resolution is 0.84 cm. With these resolutions satisfying the requirement of the experiment, we expect that the TOF will be able to reconstruct a more precise annihilation position.