Speaker
Summary
The Payload for Antimatter-Matter Exploration and Light Nuclei Astrophysics
(PAMELA), primarily designed to directly measure antiparticles (antiprotons and
positrons) in the cosmic radiation, was launched successfully on June 15th,
2006, and, since then, it is in continuous data taking. The calorimeter of the
PAMELA apparatus has been designed to identify antiprotons from an electron
background and positrons from a background of protons with high efficiency
and rejection power. It is a sampling silicon-tungsten imaging calorimeter, which
comprises 44 single-sided silicon sensor planes (380 µm thick) interleaved with
22 plates of tungsten absorber (0.74 X0 each). It is the first silicon-tungsten
calorimeter to be launched in space.
In this work we present the in-orbit performance of the calorimeter, including
the measured identification capabilities. We show that the calorimeter provides
a proton rejection factor of ~10^5 while keeping a high efficiency in selecting
electrons and positrons, thus fulfilling the identification power needed to reach
the primary scientific objectives of PAMELA. We show also that, after almost two
years of operation in space, the calorimeter is still performing nominally.
