Development of the Electromagnetic Calorimeter for the Precise Measurement of the Cosmic Ray Positron Fraction with PEBS

Since almost a century ago, it is known that a quarter of the energy density in the Universe is represented by the dark matter which has been seen only through gravitational interaction. Despite of intensive searches for a dark matter constituent in different methods, no positive results have been seen yet. Recently, special hopes are put into the observation of the charged cosmic rays which could bear signs of dark matter annihilation. This is due to the several anomalies observed in positron fraction and total e+ +e− flux in the cosmic rays. Since the available data do not allow to draw strong conclusion about the nature of those anomalies, a new balloon-borne experiment for the precise measurement of the cosmic ray positron fraction has been proposed. A Positron Electron Balloon Spectrometer (PEBS) is equipped with a magnetic spectrometer, a transition radiation detector, an electromagnetic calorimeter and a time of flight system, and will give the means to extend the measurement to higher energies. This thesis is devoted to the description of the development and performance study of one of the PEBS constituents - the electromagnetic calorimeter (ECAL). This sub-detector plays a key role in the PEBS performance delivering an energy measurement of incident positrons and electrons and allowing to distinguish the positrons from the vast proton background. The ECAL uses a novel approach for the light detection - silicon photomultipliers (SiPM). The understanding of the SiPM response to the large range of signals, starting from tens of photons and going up to tens of thousands of photons, is necessary in calorimetry applications. Therefore a detailed study of their operation is carried out with simulation and described in this work. During the four years of study, two prototypes of the ECAL were built and exposed to a test beam at PS and SPS facilities at CERN. The results of the prototypes performance for the energies up to 180 GeV are discussed in detail, assessing the PEBS ECAL capabilities to achieve design requirements for particle identification.