University of Wisconsin-Madison

First Year Performance Paper - Section 7

7 Summary and Plan for Completion

We have deployed and operated one string and eight surface detectors of the IceCube Neutrino Observatory in 2005. The separation between the digital optical modules on the surface and those near the bottom of the string in the deep ice is 2.5 km, comparable to the scale projected for the finished IceCube. Successful reconstruction of coincident cosmic-ray events with few nanosecond accuracy therefore demonstrates that the full detector will work as planned.

All 76 PMTs in the DOMs are working. Remote calibration of the timing and amplitude of the digital optical modules is carried out successfully as part of the normal operation of the detector. Tests with downward cosmic-ray muons and with artificial flashers demonstrate that timing accuracy at the level of a few nanoseconds is maintained over all the DOMs. These accurate calibrations have allowed the reconstruction of the first upward-going candidate neutrino induced events with unambiguous time patterns on more than 30 DOMs. The zenith angle distribution of atmospheric muons has been reconstructed with String-21 and the time residuals for each DOM have been measured using muons. The ability to reconstruct waveforms with few nanosecond resolution will be a powerful tool for analysis of complex events.

The presence of a surface array above a neutrino telescope is a unique feature of IceCube. It will enable an exploration of the cosmic-ray spectrum using the combined measurement of the electromagnetic and muon components of atmospheric showers at energies from below the knee up to 1018 eV with unprecedented statistics and energy resolution. Charge spectra of the DOMs in the 8 IceTop tanks exhibit a muon peak at about 240 PE indicating a nominal energy deposition of 0.8 MeV/photoelectron, and the data indicate a uniform response as a function of the deposited energy in the tanks. The direction of showers has been reconstructed and the expected sec(↕) dependence is observed.

During the austral summer of December 2005 - January 2006 eight more strings of 60 DOMs each have been deployed in the ice along with 12 additional surface stations. After the new strings are commissioned, the number of operating DOMs with 10 inch PMTs in IceCube will be comparable to the total number of 8 inch PMTs in the AMANDA modules. Because of the larger spacing the effective volume of the combined neutrino detector will be twice that of AMANDA II and somewhat larger for higher energy events (> 10 TeV). This will allow the experiment to start physics analysis, and in a few years the discovery of the first astrophysical neutrinos is a realistic possibility. With 33 sixteen stations on the surface the combined detector will also be sensitive to cosmic-rays up to 1017 eV.

The construction is scheduled to advance at a rate of 14 or more strings and tank stations per year in successive seasons until the detector reaches its final configuration in 2011. The plan calls for 4800 In-Ice DOMs on 80 strings, distributed in a volume of 1 km3 in a triangular pattern with 125 m lateral spacing and at depths from 1450 to 2450 m. The surface array will comprise 160 frozen water tanks each containing 2 DOMs, which constitute 80 stations arranged in pairs associated with each string.