Dark noise calibration of the Super-Kamiokande outer detector

Abstract

The process for calculating the single photoelectron gain in the Super-Kamiokande outer detector has been streamlined. The original technique used optic fibers to expose the detector's photomultiplier tubes to known amounts of light in order to determine the signal response to one photoelectron. This process was long and required data collection to halt during calibration. The new technique makes use of the background noise hits that are recorded in the time before an event that triggers the outer detector. By assuming that these hits are single photoelectrons, the data points provide a charge calibration that is fast, does not intrude on data collection, and presents little compromise of accuracy. The dark noise calibration technique has already been used to adjust the voltage supplies to the photomultiplier tubes so that their gains are more uniform. It also makes it possible to check the long term stability of the gain calibration.