3 Science Motivation for Kilometer-Scale Detectors
The main goal of the IceCube project is the detection of extraterrestrial sources of very high energy neutrinos [19, 50, 51].
- IceCube will reach a sensitivity for diffuse fluxes of a few 10-9·E-22 GeV-1 cm-2 s-1, which is more than one order of magnitude below conservative "upper bounds" derived from cosmic-ray observations, and three orders of magnitude below bounds derived from gamma ray observations alone. The published AMANDA limit has already improved previous experimental limits by more than a factor 10 and will be improved by AMANDAII and IceCube by roughly an additional 1.0 and 2.5 orders of magnitude, respectively. Within this range of sensitivity, models predict between "several" and thousands of events per year.
- Point source searches will reach a sensitivity of at least 10-12 cm-2 s-1 for energies greater than about 10 TeV. This is nearly two orders of magnitude below the observed Mrk501 TeV gamma-ray flux during its flaring phase. Predictions for some steady or quasi-steadysources reach a few tens of events per year.
- Supernova models predict 10-100 events shortly before and after the SN burst.
- Gamma Ray Bursts are expected to yield 10-100 events per year.
- IceCube has also significant EeV capabilities. Event numbers predicted by top-down scenarios (like topological defects) lead to 1-30 events per year, comparable to expectations for dedicated EeV experiments.
- IceCube has a realistic chance to identify tau neutrinos via "double-bang" events, with up to 100 events per year expected for certain topological defect models.
IceCube is a multi-purpose detector. Beside high energy neutrino astronomy, it can be used to investigate a series of other questions:
- Magnetic monopoles: Present limits for the flux of relativistic monopoles can be improved by two orders of magnitude. This is a factor of 1000 below the Parker bound [52]. One also can search for slow monopoles catalyzing proton decay, or for strange quark matter.
- Neutrinos from WIMP annihilation: IceCube can play a complementary role to future direct detection experiments, particularly for high WIMP masses. The instrument is unique for TeV dark matter.
- MeV neutrinos from supernova bursts: IceCube will detect a supernova burst over the whole Galaxy, and as far as the Magellanic clouds.
- As a by-product, neutrino oscillations, physics (and gamma-ray astronomy) with downgoing muons, or even questions of glaciology can be investigated.
Discovery of any single one of the high energy signals listed above would unquestionably make IceCube a resounding success. However, as a detector one hundred times larger than AMANDA and one thousand times larger than any underground detector, IceCube will be opening a new window on the universe, and as such holds out even greater promise: the exciting discovery of unanticipated phenomena.
