PAMELA: a satellite experiment for antiparticles measurement in cosmic rays

PAMELA is a satellite-borne experiment that will study the antiproton and positron fluxes in cosmic rays in a wide range of energy (from 80 MeV up to 190 GeV for antiprotons and from 50 MeV up to 270 GeV for positrons) and with high statistics, and to measure the antihelium/helium ratio with a sensitivity of the order of 10^-8. It will fly on-board of a polar orbiting Resurs DK1 satellite, going to be launched into space by a Soyuz TM2 rocket in 2004 from Baikonur cosmodrome in Kazakistan, for a 3 year long mission. Particle identification and energy measurement is performed in the PAMELA experiment using the subdetectors it is composed of: a magnetic spectrometer made up of a permanent magnet equipped with double-sided microstrip silicon detectors, an electromagnetic imaging calorimeter composed of layers of tungsten absorber and silicon detectors planes, a transition radiation detector made by straw tubes interleaved with carbon fiber radiators, a plastic scintillator time-of-flight and trigger system, a set of anticounter plastic scintillator detectors and a neutron detector. The features of the detectors and the main results obtained in test beam sessions are presented.