28th International Cosmic Ray Conference 2141 The Time-of-Flight System of the PAMELA Experiment

The PAMELA satellite-borne experiment, scheduled to be launched in 2004, is designed to provide a better understanding of the antimatter component of cosmic rays. In the following we report on the features and performances of its scintillator telescope system which will provide the primary experimental trigger and time-of-flight particle identification. 1. Detector description The Time-of-Flight (ToF) system of PAMELA experiment [1] is composed of several layers of plastic scintillators read out by Photo-Multiplier Tubes (PMTs). The ToF must fulfill the following goals: • provide a fast signal for triggering data acquisition in the whole instrument; • measure the flight time of particles crossing its planes, once this information is integrated with the measurement of the trajectory length through the instrument, their velocity β can be derived. This feature enable also the rejection of albedo particles; • determine the absolute value of charge z of incident particles through the mul-tiple measurement of energy loss dE/dx in the scintillator counters. 1.1. ToF layout The ToF, as showed in Fig. 1., will be divided in 6 layers, arranged in three planes, each plane composed of two layers. The overall geometry of the ToF layers is summarized in Tab. 1.. Mechanical structure Both ends of each scintillator paddle are glued to a one-piece adiabatic UV-transparent Plexiglas light guide. This is in turn mechanically coupled to a pp. 2141–2144 c©2003 by Universal Academy Press, Inc. 2142 PMT by means of optical pads. Scintillators and light-guides are wrapped in a 25 µm thin Mylar foil. The S3 plane will be housed directly in the base plate of PAMELA and kept in place by a set of steel frames. The other two planes will be enclosed in light-proof boxes. The external shell of these boxes is 300 µm thick Avional, and the space between the box and the scintillators is filled with a one-piece PVC mask