Flight Calibration of the Photodetector in the TUS Detector

A technique is proposed for carrying out flight calibration of a photomultiplier tubes (PMTs) of the photodetector in the orbital TUS detector of ultra-high-energy cosmic rays in the absence of a calibration signal. The new technique consists in calculating two statistical characteristics of digitized signals from detected events (their mean value A and variance $$\sigma _{A}^{2}$$ ) and constructing the linear approximation $$\sigma _{A}^{2}$$ (A) for stationary signals. This technique has been tested in a laboratory experiment with a photodetector module, which is identical to the modules used in the detector. As a result, the gains of most photodetector channels of the TUS detector have been estimated again and the changes that occurred (in particular, the “aging effect”) have been analyzed.