In Situ Measurement of the IceCube DOM Efficiency Factor Using Atmospheric Minimum Ionizing Muons

Abstract

The IceCube Neutrino Observatory is a large scale neutrino detector embedded deep within the Antarctic ice located at the geographical South Pole. It instruments over one cubic kilometre of ice with 5,160 Digital Optical Modules (DOM), each of which houses a 10 inch diameter photomultiplier tube (PMT). Deep in the centre of the detector is a densely instrumented region known as DeepCore which lowers the detection threshold for low energy physics analyses. DOMs in DeepCore contain a PMT with a higher quantum efficiency than the rest of IceCube, resulting in a higher sensitivity to photons. Through the use of the PMTs, IceCube captures Cherenkov light produced by high energy charge particles created in neutrino interactions. Extensive inlab tests of the DOM’s behavior have been done and the characteristics parameterized, but once frozen in the ice, absolute direct in situ calibration is difficult. Utilizing a sample of atmospheric minimum ionizing muons, selected for their well modeled behavior, charge measurements are compared between the active detector and a Monte Carlo simulation intended to replicate the detector’s response. Potential in situ effects can cause a discrepancy between the signal response and simulation response. This difference between the real signal and simulation can then be used to construct a scaling factor, the DOM efficiency, to compensate for such effects. By using this method, the DOM efficiency factor that best describes the IceCube DOMs is 0.984 ± 0.023, and for DeepCore DOMs 0.923 ± 0.033, indicating a slight excess of detected charge in simulation.