The AQUA-RICH atmospheric neutrino experiment

We describe a 125 m diameter spherical detector containing 1 Mt of water, capable of high rate observation of atmospheric neutrino events (30000/y). The ring imaging Cherenkov (RICH) technique is used to measure velocity, momentum and direction of particles produced by neutrinos interacting in water. The detector will be sited outdoors (under a 50 m water shield) in a natural (further excavated) pit. probably in Sicily. Spherical reflecting mirrors focus Cherenkov light produced by secondaries from interacting neutrinos. Photons are detected by 5310 hybrid photodiodes (WPDs) of 1 m diameter each with 396 pads of 45 x 45 mm(2) on the photocathode surface, demagnified to 9 x 9 mm(2) on the silicon sensor. For most tracks the ring width will be dominated by multiple scattering which should allow momentum to be determined. Hadrons of momentum p less than or equal to 5 GeV/c can be measured with sigma(p)/p less than or equal to 7% and muons of p less than or equal to 32 GeV/c with sigma(p)/p less than or equal to 1%. The ring center determines track direction with sigma(theta x), sigma(theta y) approximate to 6 mrad. Track reconstruction in water will require time resolution sigma(t) < 1 ns. Detection of oscillating muon signals (disappearance)is feasible with atmospheric neutrinos and precision measurement of oscillation parameters is feasible for 10(-2) less than or equal to Delta m(2) less than or equal to 10(-4) eV(2). Tau or sterile neutrino appearance experiments are also possible with atmospheric neutrinos. Other physics topics addressable with this detector are proton decay, supernova detection and search for astrophysical neutrino sources. A first lest module of 3 tons water and 120 PMs (32 mm phi) will operate (5/99) with 1-3 GeV muons in a CERN-PS test beam to verify the momentum algorithm. A second (6 m)(3) test module with 216 tons of water and 25 HPDs (0.25 m phi) is designed to observe full multi-track images and test pattern recognition and ring reconstruction algorithms. (C) 1999 Elsevier Science B.V. All rights reserved.