Calibration and Characterization of the IceCube Photomultiplier Tube

TL;DR

This paper details the laboratory calibration and characterization of over 5,000 Hamamatsu R7081-02 photomultiplier tubes for the IceCube neutrino observatory, focusing on their optical, timing, and charge response properties.

Contribution

It provides comprehensive calibration procedures and parameterizations for the PMTs, enhancing the accuracy of IceCube's event detection and reconstruction capabilities.

Findings

Charge spectrum parameterizations established

Timing resolution and afterpulse characteristics measured

Photon detection efficiency calibrated with Rayleigh scattering

Abstract

Over 5,000 PMTs are being deployed at the South Pole to compose the IceCube neutrino observatory. Many are placed deep in the ice to detect Cherenkov light emitted by the products of high-energy neutrino interactions, and others are frozen into tanks on the surface to detect particles from atmospheric cosmic ray showers. IceCube is using the 10-inch diameter R7081-02 made by Hamamatsu Photonics. This paper describes the laboratory characterization and calibration of these PMTs before deployment. PMTs were illuminated with pulses ranging from single photons to saturation level. Parameterizations are given for the single photoelectron charge spectrum and the saturation behavior. Time resolution, late pulses and afterpulses are characterized. Because the PMTs are relatively large, the cathode sensitivity uniformity was measured. The absolute photon detection efficiency was calibrated using Rayleigh-scattered photons from a nitrogen laser. Measured characteristics are discussed in the context of their relevance to IceCube event reconstruction and simulation efforts.