T2K neutrino flux prediction

Abstract

The Tokai-to-Kamioka (T2K) experiment studies neutrino oscillations using an off-axis muon neutrino beam with a peak energy of about 0.6 GeV that originates at the J-PARC accelerator facility. Interactions of the neutrinos are 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 neutrino interaction rates at the T2K detectors and is an important input to T2K neutrino oscillation and cross section measurements. A FLUKA and GEANT3 based simulation models the physical processes involved in the neutrino production, from the interaction of primary beam protons in the T2K target, to the decay of hadrons 3 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.

Measurements of neutrino oscillation in appearance and disappearance channels by the T2K experiment with6.6×1020protons on target

“…The proton beam properties have been stable throughout T2K operation, and their values and uncertainties for the most recent T2K run period, Run 4, are given in Table II. The values for other run periods have been published previously [11]. The neutrino beam position and width stability is also monitored by the INGRID detector, and the results are given in Sec.…”

“…The hadron production data used for the oscillation analyses described here are equivalent to those used in our previous publications [3,11], including the statistics-limited NA61/SHINE data set taken in 2007 on a thin carbon target. The NA61/SHINE data analyses of the 2009 thin-target and T2K-replica-target data are ongoing, and these additional data will be used in future T2K analyses.…”

“…Dates energy for each neutrino flavor [11]. Table III shows the breakdown for the ν μ and ν e flux uncertainties for energy bins near the peak energy.…”

“…Horn and target alignment uncertainties come from survey measurements. Systematic uncertainties in modeling particle multiplicities from hadronic interactions come from several sources: experimental uncertainties in the external data, the uncertain scaling to different incident particle momenta and target materials, and extrapolation to regions of particle production phase space not covered by external data [11]. The overall uncertainty is described by calculating the covariance of the pion, kaon, and secondary nucleon multiplicities and their interaction lengths.…”

“…The secondary beam line is simulated in order to estimate the nominal neutrino flux (in absence of neutrino oscillations) at the near and far detectors and the covariance arising from uncertainties in hadron production and the beam line configuration [11]. We use the FLUKA 2008 package [12,13] to model the interactions of the primary beam protons and the subsequently produced pions and kaons in the graphite target.…”