Delia Tosi (UW Madison / WIPAC)
The IceCube neutrino observatory is composed of more than five thousand Digital Optical Modules (DOMs), installed on the surface and at depths between 1500 and 2500 m in clear ice at the South Pole. Each DOM incorporates a 10” diameter photomultiplier tube (PMT) intended to detect light emitted when high energy neutrinos interact with atoms in the ice. Depending on the energy of the neutrino and the distance from debris particle tracks, PMTs can be hit by up to several thousand photons. The number of photons per PMT and their time distribution is used to reject background events and to determine the energy and direction of each neutrino. The detector energy scale was established with good precision independent of lab measurements on DOM optical sensitivity, based on light yield from stopping muons and calibration of ice properties. A laboratory setup has now been developed to more precisely measure the DOM optical sensitivity as a function of angle and wavelength. DOM sensitivities are measured in water using a broad beam of light whose intensity is measured with a NIST calibrated photodiode. This study will refine the current knowledge of IceCube response and lay a foundation for future precision upgrades to the detector.