First oscillation analysis using neutrino and antineutrino data at T2K

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 ${\nu }_{\mu }/{\overline{\nu }}_{\mu }$ disappearance and ${\nu }_e/{\overline{\nu }}_e$ appearance data are analysed using a Bayesian Markov Chain Monte Carlo method, providing the first ever sensitivity to the CP-violating phase δ_CP from T2K data alone. The T2K data favour near-maximal mixing, with sin² θ ₂₃ and $\Delta m_{32}^2$ consistent with previous T2K measurements, a value of sin² θ ₁₃ consistent with measurements by reactor experiments, and δ_CP close to -π/2. When fitting with T2K data alone, the 90% credible interval for δ_CP disfavours values around π/2: δ _CP ∉ [0.38, 2.60] rad. When using a prior on sin² 2θ ₁₃ from reactor measurements, the 90% credible interval contains δ_CP ∉ [−3.10, −0.17] rad, disfavouring the CP-conserving values 0 and ±π. The effect on this result of the δ_CP prior is also investigated and presented. (paper)