Double beta decay  Atmospheric neutrinos  Externally produced events

Future

It is clear that we have an experimental problem for both categories of events. The question is whether it can be solved in the future. It is not only a problem of statistics but also of systematics connected with the quality of detectors. The detectors that currently are taking data are: 1) Internal events: SOUDAN2, MACRO, Superkamiokande.
Superkamiokande began operation in April 1996. The Multi-GeV events are now contained (due to the dimensions) and the quality of the data is improved because of the larger PM coverage. Starting in 1999, it is planned to take data with a long base line (250 km) 1.4 GeV $\nu_\mu$ beam with a 1000-ton water Cerenkov near detector. This detector can be used at the beginning to check the systematic error of the far detector for atmospheric neutrinos. After 2-3 years of running with the long base line neutrino beam (around 2002-2003), Superkamiokande should check directly with disappearance experiments the oscillation pattern resulting from the current water Cerenkov atmospheric neutrino data. 2) External events: currently are taking data Superkamiokande, Baksan, MACRO.
There are four new detectors under construction that could give information on the atmospheric neutrino problem: Icarus, Nestor, Baikal, Amanda. Icarus will be very interesting for neutrino internal events. The mass will not be competitive with Superkamiokande, but the event pattern will be much cleaner. Nestor is an underwater Cerenkov detector, to be located in the Mediterranean sea, near Pilos in Greece. The first stage of the project will consist of a tower having a nominal area of about 2000 m² for E>5 GeV and 20000 m² for E> 1 TeV. The collaboration has chosen to maximise the surface for high-energy muons, so it will not be competitive with Superkamiokande for internal events, but should be interesting for external events. Baikal is an underwater Cerenkov detector in the Baikal lake at a depth of 1300 m. The final detector should have an effective area of 2300 m² for E$\mu > 1$ TeV. Amanda is an under-ice Cerenkov detector, to be located near the US South Pole base. The final area is expected to be similar to that of Nestor. For atmospheric neutrinos, the same consideration as those for Nestor.