First oscillation analysis using neutrino and antineutrino data at T2K

Abstract

We present details of the first T2K neutrino and antineutrino oscillation results, in which data collected using both a muon neutrino-enhanced neutrino beam and a muon antineutrino-enhanced neutrino beam are analysed, equating to 7.002×1020 protons on target (POT) and 7.471×1020 POT respectively. Both disappearance and appearance data are analysed using a Bayesian Markov Chain Monte Carlo method, providing the first ever sensitivity to the CP-violating phase δCP from T2K data alone. The T2K data favour near-maximal mixing, with sin2 θ23 and consistent with previous T2K measurements, a value of sin2 θ13 consistent with measurements by reactor experiments, and δCP close to -π/2. When fitting with T2K data alone, the 90% credible interval for δCP disfavours values around π/2: δCP ∉ [0.38, 2.60] rad. When using a prior on sin2 2θ13 from reactor measurements, the 90% credible interval contains δCP ∉ [−3.10, −0.17] rad, disfavouring the CP-conserving values 0 and ±π. The effect on this result of the δCP prior is also investigated and presented.