The T2K Collaboration reports a precision measurement of muon neutrino disappearance with an off-axis neutrino beam with a peak energy of 0.6 GeV. Near detector measurements are used to constrain the neutrino flux and cross section parameters. The Super-Kamiokande far detector, which is 295 km downstream of the neutrino production target, collected data corresponding to 3.01 × 1020 protons on target. In the absence of neutrino oscillations, 205 ± 17 (syst) events are expected to be detected while only 58 muon neutrino event candidates are observed. A fit to the neutrino rate and energy spectrum, assuming three neutrino flavors and normal mass hierarchy yields a best-fit mixing angle sin2(Θ23) = 0.514 ± 0.082 and mass splitting |Δm232| = 2.44+0.17-0.15 × 10-3 eV2/c4. Our result corresponds to the maximal oscillation disappearance probability.
Bibliographical noteFunding Information:
Financial support was provided by Biogen Idec, Merck Serono, Bayer Healthcare, Teva Pharmaceutical Industries, ‘La Caixa’ (Spain), Fundación Obra Social Caja Madrid (Spain) and Acadèmia de Ciències Mèdiques i de la Salut de Catalunya i de Balears (Spain).
Financial support was provided by Biogen Idec, Merck Serono, Bayer Healthcare, Teva Pharmaceutical Industries, 'La Caixa' (Spain), Fundaci?n Obra Social Caja Madrid (Spain) and Acad?mia de Ci?ncies M?diques i de la Salut de Catalunya i de Balears (Spain).
© 2013 American Physical Society.