Initial results from the CHOOZ long baseline reactor neutrino oscillation experiment

M Apollonio, A Baldini, C Bemporad, E Caffau, F Cei, Y Déclais, H de Kerret, B Dieterle, A Etenko, J George, G Giannini, M Grassi (+27 others)
1998 Physics Letters B  
Initial results are presented from CHOOZ, a long-baseline reactor-neutrino vacuum-oscillation experiment. Electron antineutrinos were detected by a liquid scintillation calorimeter located at a distance of about 1 km. The detector was constructed in a tunnel protected from cosmic rays by a 300 MWE rock overburden. This massive shielding strongly reduced potentially troublesome backgrounds due to cosmic-ray muons, leading to a background rate of about one event per day, more than an order of
more » ... han an order of magnitude smaller than the observed neutrino signal. From the statistical agreement between detected and expected neutrino event rates, we find (at 90% confidence level) no evidence for neutrino oscillations in the electron antineutrino disappearance mode for the parameter region given approximately by deltam**2 > 0.9 10**(-3) eV**2 for maximum mixing and (sin(2 theta)**2) > 0.18 for large deltam**2.
doi:10.1016/s0370-2693(97)01476-7 fatcat:22biiw74enawdco4qy5es4wt3y