Recent Progress on the GAPS Time of Flight System

Abstract

The General AntiParticle Spectrometer (GAPS) is a balloon-borne cosmic-ray antimatter experiment that uses the exotic atom technique, eliminating the requirement for strong B-fields used by conventional magnetic spectrometers. It will be sensitive to antideuterons with kinetic energies of 0.05-0.25 GeV / nucleon, which are highly motivated candidates for indirect dark matter detection. Moreover, GAPS will provide new information on the antiproton spectrum from $0.07<T<0.25$ GeV. The GAPS design is based on a lithium drifted silicon tracker and plastic scintillator time of flight (TOF) system. The latter is the focus of this contribution. Currently, the TOF system includes an outer "umbrella" consisting of 132 counters covering an area of 38 m$^2$ and a nearly hermetic inner "cube" with 64 counters and area of 15 m$^2$. The counters will be mechanically secured to the gondola using an innovative carbon fiber structure. Each end of the 196 counters will be read out using a silicon photomultiplier (SiPM) based analog front end with a high gain timing channel and low gain trigger channel. The high gain channel is sampled and digitized with a custom readout board that uses the DRS-4 ASIC. A local trigger monitors multiple programmable threshold levels for all 392 counter ends. A master trigger analyzes the local trigger hit patterns and initiates a TOF read out for an interesting event. A central computer then analyzes and estimates key observables. This contribution summarizes the design, performance, and prototype development of the TOF system and the path going forward in 2019 and 2020 towards construction and integration of the system.