First measurement of the muon neutrino charged current single pion production cross section on water with the T2K near detector

The T2K off-axis near detector, ND280, is used to make the first differential cross section measurements of muon neutrino charged current single positive pion production on a water target at energies ∼ 0.8 GeV. The differential measurements are presented as a function of the muon and pion kinematics, in the restricted phase space defined by p_π+ > 200 MeV/c, p_μ > 200 MeV/c, cosθ_π+ > 0.3 and cos(θ_μ) > 0.3. The total flux integrated ν_μ charged current single positive pion production cross section on water in the restricted phase space is measured to be <σ>_φ = 4.25 ± 0.48(stat) ± 1.56(syst) x 10^-40 cm²/nucleon. The total cross section is consistent with the NEUT prediction (5.03 x 10^-40) cm²/nucleon) and 2 σ lower than the GENIE prediction (7.68 x 10^-40 cm²/nucleon). The differential cross sections are in good agreement with the NEUT generator. The GENIE simulation reproduces well the shapes of the distributions, but overestimates the overall cross section normalization. (authors)