Uli Katz: The Orca Project
As a way of introduction the speaker discussed how a neutrino telescope works. A upward-going neutrino produces an interaction in the rock below the detector, and the charged secondaries cross the detector volume (water or ice), stimulating Cherenkov radiation. This can be recorded by a 3-D array of photosensors. Backgrounds come from irreducible atmospheric neutrinos from cosmic-ray interactions in the atmosphere, atmospheric muons, and Sea water light. The firs source is an important calibration source, and allows for oscillation studies. Atmospheric muons from above highly exceed the neutrino event rate.
Antares has shown the capability of measuring neutrino oscillations although they are not optmized for that task. In alternative to Km3Net, which focuses on neutrino astronomy, Orca can study oscillations with cosmic rays. It will only be pursued if the mass hierarchy measurement is found possible. Currently Orca is a feasibility study and not yet a concrete proposal.
The optical module envisions many small PMT in a 17-inch glass sphere. The footprint of Orca is intentionally randomized in a 150×150 meter area.
The major experimental questions are on trigger and selection efficiencies, systematic effects, backgrounds. They are still in the early phase of investigating these.
The speaker then discussed whether it is justified to pursue ORCA and PINGU simultaneously, when they aim at the same physics and have similar expected reaches. He mentioned that he heard a remark from a colleague who said he would have never believed the Higgs boson results by the LHC collider if these had come from a single experiment. I found the remark rather silly, in the face of the overwhelming evidence that is being presented in multiple final states by each of the two experiments, but I ascribed it to ignorance rather than malign attitude toward these experiments.