Direct evidence for neutrino flavour transformation from neutral-current interactions in SNO

by Art McDonald (Queen's University, Canada)

Tuesday 21 May 2002, 16:30 → 17:30 Europe/Zurich

500/1-001 - Main Auditorium (CERN)

The Sudbury Neutrino Observatory (SNO) is a 1,000 tonne heavy water Cerenkov-based neutrino detector situated 2,000 meters underground in INCO's Creighton Mine near Sudbury, Ontario, Canada. For the neutrinos from ⁸B decay in the Sun, SNO observes the Charged Current (CC) neutrino reaction sensitive only to electron neutrinos and observes others (Neutral Current and Elastic Scattering) sensitive to all active neutrino types. SNO can thereby search for direct evidence of neutrino flavour change. Using these reactions and assuming the standard ⁸B spectral shape, the electron neutrino component of the ⁸B solar flux is 1.76 ±0.05 (stat) ± 0.09 (syst) x 10⁶ cm^-2 s^-1 for a kinetic energy threshold of 5 MeV. The non-n_e active component is f_mt = 3.41 ±0.45 (stat) +0.48 -0.45 (syst) x 10⁶ cm^-2 s^-1, 5.3 s greater than zero, providing direct evidence for solar n_e flavour transformation. The total flux measured with the NC reaction, with no assumption of ⁸B spectral shape, is 6.42 ±1.57 (stat) +0.55 - 0.58 (syst), in good agreement with the flux calculated with standard solar models. For CC events, assuming an undistorted ⁸B spectrum, the night minus day rate is 14.0% ± 6.3% +1.5% - 1.4% of the average rate. A global solar neutrino analysis in terms of matter-induced oscillations of two active flavours strongly favours the Large Mixing Angle solution.

Organiser(s): Jasper Kirkby / EP Division

Note: Tea & coffee will be served at 16.00 hrs.