Performance of the AMS-02 Electromagnetic Calorimeter in Space

AMS-02(Alpha Magnetic Spectrometer) is an high energy particle detector developed to operate on the International Space Station. AMS-02 was installed on ISS on May 2011 and is expected to operate for 10-20 years collecting about 160-320 billions of events. The main goals of the experiment are the detection of primordial antimatter and dark matter by studying spectra and flux of different cosmic ray components (protons, electrons, nuclei, positrons, antiprotons, gamma rays, etc) in the high energy range (1-2000 GeV). Identification of electrons, positrons and photons is provided by the Electromagnetic Calorimeter (ECAL), a fine grained lead-scintillating fibers sampling calorimeter that allows for a precise three-dimensional imaging of the longitudinal and lateral shower development. It provides an excellent reconstruction of electromagnetic shower energy and a highly efficient rejection of the hadronic background. Thanks to the 3D shower reconstruction capability, ECAL allows a stand-alone determination of the incoming particle direction, with unprecedented angular resolution. As a result, ECAL is able to identify high energy photons coming from galactic or extragalactic sources.