Precision measurement of µ disappearance by T2K

T2K is a long-baseline neutrino oscillation experiment, where a muon neutrino beam is produced at the J-PARC facility and after traveling 295 km it is detected by SuperKamiokande, a water Cherenkov detector with a 22.5 kton fiducial mass. One aim of the experiment is to precisely determine the mixing angle θ23 and the mass squared difference ∆m23 using a measurement of muon neutrino disappearance. The T2K accumulated dataset is 6.57 × 10 protons on target, which is 8% of the experimental goal. Here we present an analysis of the T2K muon neutrino disappearance data and the worlds best constraint on the value of the mixing angle θ23 obtained by this analysis.