Calibration and equalisation of plastic scintillator detectors for antiproton annihilation identification over positron/positronium background

In this contribution, the system of the external plastic scintillator slabs of the AEgIS experiment is presented. These slabs, surrounding the superconducting magnet and operating at room temperature, are read out by photomultiplier tubes (PMTs) that are calibrated and equalised to be exploited as a whole detector with useful segmentation and redundancy to effectively detect single antiparticle annihilations. In particular, thanks to periodically recurring calibrations with cosmic rays and to a detailed study of the system in different operational conditions, including extensive Monte Carlo (MC) simulations, these scintillators can be used to identify antiproton annihilations over the constant background represented by cosmic rays and over the strongly time-dependent background due to positrons/positronium annihilations. By means of the sampling and digitization of the analog signal produced by each phototube and the consequent analysis of the amplitude of the recorded events, the energy released by the particle in the scintillator slab can be estimated consistently and with good accuracy. As a consequence, we are able to identify an amplitude range where positrons/positronium annihilations can be univocally excluded. This prerequisite allows us to exploit the array of external plastic scintillators for antihydrogen annihilations tagging.