The T2K Neutrino Flux Prediction

The Tokai-to-Kamioka ( T2K) experimentstudies neutrino oscillationsusing an off-axis muon neutrinobeam with a peak energy of about 0.6 GeV that originates at the J-PARCaccelerator facility. Interactions of the neutrinosare observed at near detectors placed at 280 m from the production target and at the far detector -- Super-Kamiokande(SK) -- located 295 km away. The flux prediction is an essential part of the successful prediction of neutrinointeraction rates at the T2K detectors and is an important input to T2K neutrino oscillationand cross section measurements. A FLUKA and GEANT3 based simulation models the physical processes involved in the neutrinoproduction, from the interaction of primary beam protons in the T2K target, to the decay of hadrons and muons that produce neutrinos. The simulation uses proton beam monitor measurements as inputs. The modeling of hadronic interactions is re-weighted using thin target hadron production data, including recent charged pion and kaon measurements from the NA61/SHINE experiment. For the first T2K analyses the uncertainties on the flux prediction are evaluated to be below 15% near the flux peak. The uncertainty on the ratio of the flux predictions at the far and near detectors is less than 2% near the flux peak.