Geometry Calibration of IceCube : using Photon Timing from Downgoing Muons

Abstract: The IceCube Neutrino Observatory at the South Pole has instrumented one cu-bic kilometer of ice by deploying digital optical modules (DOMs) in 86 drillholes, each containing a string of DOMs. So far IceCube has used the locationof the drill tower for the positions of DOMs in the transverse directions (x andy) to the vertical direction (z). Attempts to improve on this have so far failed.This thesis presents a new method for calibrating the positions of the DOMs.For a large selection of muon tracks, a maximum likelihood-based approach isused to determine the positions of DOMs. As a proof of concept, four centralstrings are studied to keep systematics uncertainties as low as possible. Themethod can find x and y (z) positions to 0.2m (0.5m) as found using simulationcorresponding to four days of data. In four days of real data we find that thereconstructed z position has a systematic offset of around 5m, which is not aphysical shift as the positions are known to 0.2m. For the x and y positions theresults are consistent with nominal positions except for string 36. As string 36is a string at the center of the IceCube array, it should be the most symmet-ric and an accurate estimate could indicate that the method has found a realdeviation.