J. Maneira: The Sudbury Neutrino Observatory (SNO)
Jose Maneira (LIP) gave a talk on the SNO experiment, starting with a brief history of the endeavour.
While the flux of observed neutrino interactions from Sun-generated neutrinos was known for many years to be in deficit, the situation could not be clarified until one could measure neutral-current interactions: these provide a flux measurement that is independent on the possibility of neutrino oscillations between different flavors. The SNO detector was built with precisely that aim. This could be achieved by detecting the neutron emitted in the final state of a neutrino interaction on deuteron target.
In the first phase of operation of SNO, neutrons were detected by deuteron capture. In phase 2 the neutrons were captured by chlorine; in phase 3 Helium-3 was used. This latter method went operational in 2004.
Results from a statistical analysis proved that neutrinos oscillate, so that only a third of the total flux of solar neutrinos is composed of electron neutrinos. Later, a combined fit of data from the three phases of operation extracted the flux of boron-eight solar neutrinos, and a parametriation of the oscillation survival probability. This ended up providing crucial input for a good precision of the theta_12 mixing parameter.
An upgrade to SNO+ involves a change of scope: it consists in replacing heavy water with 780 tons of liquid scintillator, loading it with 3900kg of Tellurium, to search for neutrinoless double beta decay of 130Te. The expected result is T(1/2)> 1.96×10^26 years, at 90% Confidence Level.