The trigger logic of EUSO-SPB and its performance

Abstract

EUSO-SPB (Extreme Universe Space Observatory - Super Pressure Balloon) is the first path-finder mission of the JEM-EUSO program which hosts a trigger logic following the concept envisaged for the main mission. Prior to its implementation the logic has been tested offline by means of dedicated simulations and experimental data taken at the TurLab facility as well as by the previous path-finder missions EUSO-Balloon and EUSO-TA. All these tests allowed optimizing the performance of the algorithm, especially in terms of controlling the rate of fake events due to other types of luminous phenomena such as anthropogenic lights, airplanes, lightnings, meteors, etc. Due to the necessity of limiting the logic to a single level trigger, quite some efforts have been devoted to its codification and implementation in the Photo-Detector Module of EUSO-SPB which is the main board exploiting the trigger logic and controlling the front-end electronics. The performance of the implemented logic has been then verified by means of dedicated tests carried out in a field campaign at the Telescope Array site where the EUSO-SPB detector was exposed to the night sky luminosity and to a variety of point-like and diffused light sources such as stars, meteors, airplanes and lightnings. Moreover, dedicated tests were performed using the Central Laser Facility of Telescope Array and a mobile laser system of the Colorado School of Mines with variable intensity to mimic up-going cosmic ray showers and determine experimentally the triggering performance of EUSO-SPB. The trigger logic scheme and its hardware implementation as well as the results of the field tests carried out at the Telescope Array site in September-October 2016 and of the preliminary analyses of the data collected during EUSO-SPB flight are summarized.