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Register a new userThe T2K Neutrino Flux Prediction
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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 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.
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The Booster Neutrino Experiment (MiniBooNE) searches for numu-to-nue oscillations using the O(1 GeV) neutrino beam produced by the Booster synchrotron at the Fermi National Accelerator Laboratory (FNAL). The Booster delivers protons with 8 GeV kinetic energy (8.89 GeV/c momentum) to a beryllium target, producing neutrinos from the decay of secondary particles in the beam line. We describe the Monte Carlo simulation methods used to estimate the flux of neutrinos from the beamline incident on the MiniBooNE detector for both polarities of the focussing horn. The simulation uses the Geant4 framework for propagating particles, accounting for electromagnetic processes and hadronic interactions in the beamline materials, as well as the decay of particles. The absolute double differential cross sections of pion and kaon production in the simulation have been tuned to match external measurements, as have the hadronic cross sections for nucleons and pions. The statistical precision of the flux predictions is enhanced through reweighting and resampling techniques. Systematic errors in the flux estimation have been determined by varying parameters within their uncertainties, accounting for correlations where appropriate.
The observation of the recent electron neutrino appearance in a muon neutrino beam and the high-precision measurement of the mixing angle $theta_{13}$ have led to a re-evaluation of the physics potential of the T2K long-baseline neutrino oscillation experiment. Sensitivities are explored for CP violation in neutrinos, non-maximal $sin^22theta_{23}$, the octant of $theta_{23}$, and the mass hierarchy, in addition to the measurements of $delta_{CP}$, $sin^2theta_{23}$, and $Delta m^2_{32}$, for various combinations of $ u$-mode and (bar{ u})-mode data-taking. With an exposure of $7.8times10^{21}$~protons-on-target, T2K can achieve 1-$sigma$ resolution of 0.050(0.054) on $sin^2theta_{23}$ and $0.040(0.045)times10^{-3}~rm{eV}^2$ on $Delta m^2_{32}$ for 100%(50%) neutrino beam mode running assuming $sin^2theta_{23}=0.5$ and $Delta m^2_{32} = 2.4times10^{-3}$ eV$^2$. T2K will have sensitivity to the CP-violating phase $delta_{rm{CP}}$ at 90% C.L. or better over a significant range. For example, if $sin^22theta_{23}$ is maximal (i.e $theta_{23}$=$45^circ$) the range is $-115^circ<delta_{rm{CP}}<-60^circ$ for normal hierarchy and $+50^circ<delta_{rm{CP}}<+130^circ$ for inverted hierarchy. When T2K data is combined with data from the NO$ u$A experiment, the region of oscillation parameter space where there is sensitivity to observe a non-zero $delta_{CP}$ is substantially increased compared to if each experiment is analyzed alone.
The T2K experiment has reported the first observation of the appearance of electron neutrinos in a muon neutrino beam. The main and irreducible background to the appearance signal comes from the presence in the neutrino beam of a small intrinsic component of electron neutrinos originating from muon and kaon decays. In T2K, this component is expected to represent 1.2% of the total neutrino flux. A measurement of this component using the near detector (ND280), located 280 m from the target, is presented. The charged current interactions of electron neutrinos are selected by combining the particle identification capabilities of both the time projection chambers and electromagnetic calorimeters of ND280. The measured ratio between the observed electron neutrino beam component and the prediction is 1.01+-0.10 providing a direct confirmation of the neutrino fluxes and neutrino cross section modeling used for T2K neutrino oscillation analyses. Electron neutrinos coming from muons and kaons decay are also separately measured, resulting in a ratio with respect to the prediction of 0.68+-0.30 and 1.10+-0.14, respectively.
T2K reports its first results in the search for CP violation in neutrino oscillations using appearance and disappearance channels for neutrino- and antineutrino-mode beam. The data include all runs from Jan 2010 to May 2016 and comprise $7.482times10^{20}$,protons on target in neutrino mode, which yielded in the far detector 32 e-like and 135 $mu$-like events, and $7.471times10^{20}$,protons on target in antineutrino mode which yielded 4 e-like and 66 $mu$-like events. Reactor measurements of $sin^{2}2theta_{13}$ have been used as an additional constraint. The one-dimensional confidence interval at 90% for $delta_{CP}$ spans the range ($-3.13$, $-0.39$) for normal mass ordering. The CP conservation hypothesis ($delta_{CP}=0,pi$) is excluded at 90% C.L.
Knowledge of the neutrino flux produced by the Neutrinos at the Main Injector (NuMI) beamline is essential to the neutrino oscillation and neutrino interaction measurements of the MINERvA, MINOS+, NOvA and MicroBooNE experiments at Fermi National Accelerator Laboratory. We have produced a flux prediction which uses all available and relevant hadron production data, incorporating measurements of particle production off of thin targets as well as measurements of particle yields from a spare NuMI target exposed to a 120 GeV proton beam. The result is the most precise flux prediction achieved for a neutrino beam in the one to tens of GeV energy region. We have also compared the prediction to in situ measurements of the neutrino flux and find good agreement.
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