Analysis of the low-light response of photomultiplier tubes from the Underground Muon Detector

B. WUNDHEILER; N. GONZALES; A. LUCERO

Malargüe, Mendoza

Otro; Internal technical notes (GAP Notes); 2020

Observatorio Pierre Auger

Photomultiplier tubes have been employed as the canonical instruments to measure low-intensity radiation at the level of a few photons. Charged particles composing the air-showers generated by cosmic rays are detected by measuring the photons produced by their interaction with a medium with scintillation properties. In this context, the response of photomultiplier tubes, in particular the signal generated by single impinging photons, has been a topic of extensive research. Historically, the distribution of the charge of current pulses has been described by analytical non-linear models finely tuned with a strict choice of initial values for the fitted parameters. In this work, we assess the problem of the charge distribution of pulses generated by single impinging photons with a two- step novel procedure. We introduce the shape parameter which combines the pulse amplitude and width. Together with the pulse charge, they are fed to a principal component analysis to separate single-photon pulses from the rest of the signal. Considering an analytical model fitted to the charge distribution as the reference value, the prediction of the mean charge of single-photon pulses sprouting from our method has a bias of the order of 0.1% and a resolution of ∼ 2%.