Characterization and Absolute Calibration of R11265 Multi-Anode Photomultiplier Tubes for the JEM-EUSO Space and Balloon Program: II. Application to the EUSO-SPB2 Photodetection Modules

The fluorescence camera of the EUSO-SPB2 mission is the last and most advanced implementation of the technology developed within the JEM-EUSO (Joint Exploratory Missions for an Extreme Universe Space Observatory) collaboration to study ultra-high-energy cosmic rays (UHECRs), extensive atmospheric showers and transient luminous events from space. It consists of three photodetection modules, each hosting nine elementary cells with 36 multi-anode photomultiplier tubes (MAPMTs), for a total of 6912 pixels. The associated electronics was designed to operate in single photon counting mode. In this paper, we apply the calibration techniques presented in the accompanying paper (Paper I) to characterize the photodetectors of the EUSO-SPB2 fluorescence camera. In particular, we determine the photodetection efficiency and physical size of each pixel. We find an average efficiency of similar to 32%. We also examine its dependence with high voltage and photon wavelength, and determine the double pulse resolution of the different channels, of the order of 10 ns.