This paper presents a measurement of the charged current interaction rate of the electron neutrino beam component of the beam above $1.5$~GeV using the large fiducial mass of the T2K $pi^0$ detector. The predominant poriton of the $ u_e$ flux ($sim$8
5 %) at these energies comes from kaon decays. The measured ratio of the observed beam interaction rate to the predicted rate in the detector with water targets filled is 0.89 $pm$ 0.08 (stat.) $pm$ 0.11 (sys.), and with the water targets emptied is 0.90 $pm$ 0.09 (stat.) $pm$ 0.13 (sys.). The ratio obtained for the interactions on water only from an event subtraction method is 0.87 $pm$ 0.33 (stat.) $pm$ 0.21 (sys.). This is the first measurement of the interaction rate of electron neutrinos on water, which is particularly of interest to experiments with water Cherenkov detectors.
We report on measurements of neutrino oscillation using data from the T2K long-baseline neutrino experiment collected between 2010 and 2013. In an analysis of muon neutrino disappearance alone, we find the following estimates and 68% confidence inter
vals for the two possible mass hierarchies: Normal Hierarchy: $sin^2theta_{23}=0.514^{+0.055}_{-0.056}$ and $Delta m^2_{32}=(2.51pm0.10)times 10^{-3}$ eV$^2$/c$^4$ Inverted Hierarchy: $sin^2theta_{23}=0.511pm0.055$ and $Delta m^2_{13}=(2.48pm0.10)times 10^{-3}$ eV$^2$/c$^4$ The analysis accounts for multi-nucleon mechanisms in neutrino interactions which were found to introduce negligible bias. We describe our first analyses that combine measurements of muon neutrino disappearance and electron neutrino appearance to estimate four oscillation parameters and the mass hierarchy. Frequentist and Bayesian intervals are presented for combinations of these parameters, with and without including recent reactor measurements. At 90% confidence level and including reactor measurements, we exclude the region: $delta_{CP}=[0.15,0.83]pi$ for normal hierarchy and $delta_{CP}=[-0.08,1.09]pi$ for inverted hierarchy. The T2K and reactor data weakly favor the normal hierarchy with a Bayes Factor of 2.2. The most probable values and 68% 1D credible intervals for the other oscillation parameters, when reactor data are included, are: $sin^2theta_{23}=0.528^{+0.055}_{-0.038}$ and $|Delta m^2_{32}|=(2.51pm0.11)times 10^{-3}$ eV$^2$/c$^4$.
The Charged-Current Quasi-Elastic (CCQE) interaction, $ u_{l} + n rightarrow l^{-} + p$, is the dominant CC process at $E_ u sim 1$ GeV and contributes to the signal in accelerator-based long-baseline neutrino oscillation experiments operating at int
ermediate neutrino energies. This paper reports a measurement by the T2K experiment of the $ u_{mu}$ CCQE cross section on a carbon target with the off-axis detector based on the observed distribution of muon momentum ($p_mu$) and angle with respect to the incident neutrino beam ($theta_mu$). The flux-integrated CCQE cross section was measured to be $(0.83 pm 0.12) times 10^{-38}textrm{ cm}^{2}$ in good agreement with NEUT MC value of ${0.88 times 10^{-38}} textrm{ cm}^{2}$. The energy dependence of the CCQE cross section is also reported. The axial mass, $M_A^{QE}$, of the dipole axial form factor was extracted assuming the Smith-Moniz CCQE model with a relativistic Fermi gas nuclear model. Using the absolute (shape-only) $p_{mu}costheta_mu$ distribution, the effective $M_A^{QE}$ parameter was measured to be ${1.26^{+0.21}_{-0.18} textrm{ GeV}/c^{2}}$ (${1.43^{+0.28}_{-0.22} textrm{ GeV}/c^{2}}$).
We report a measurement of the $ u_mu$ inclusive charged current cross sections on iron and hydrocarbon in the T2K on-axis neutrino beam. The measured inclusive charged current cross sections on iron and hydrocarbon averaged over the T2K on-axis flux
with a mean neutrino energy of 1.51 GeV are $(1.444pm0.002(stat.)_{-0.157}^{+0.189}(syst.))times 10^{-38}mathrm{cm}^2/mathrm{nucleon}$, and $(1.379pm0.009(stat.)_{-0.147}^{+0.178}(syst.))times 10^{-38}mathrm{cm}^2/mathrm{nucleon}$, respectively, and their cross section ratio is $1.047pm0.007(stat.)pm0.035(syst.)$. These results agree well with the predictions of the neutrino interaction model, and thus we checked the correct treatment of the nuclear effect for iron and hydrocarbon targets in the model within the measurement precisions.
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 comp
onent 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.
New data from the T2K neutrino oscillation experiment produce the most precise measurement of the neutrino mixing parameter theta_{23}. Using an off-axis neutrino beam with a peak energy of 0.6 GeV and a data set corresponding to 6.57 x 10^{20} proto
ns on target, T2K has fit the energy-dependent nu_mu oscillation probability to determine oscillation parameters. Marginalizing over the values of other oscillation parameters yields sin^2 (theta_{23}) = 0.514 +0.055/-0.056 (0.511 +- 0.055), assuming normal (inverted) mass hierarchy. The best-fit mass-squared splitting for normal hierarchy is Delta m^2_{32} = (2.51 +- 0.10) x 10^{-3} eV^2/c^4 (inverted hierarchy: Delta m^2_{13} = (2.48 +- 0.10) x 10^{-3} eV^2/c^4). Adding a model of multinucleon interactions that affect neutrino energy reconstruction is found to produce only small biases in neutrino oscillation parameter extraction at current levels of statistical uncertainty.
The T2K collaboration reports a precision measurement of muon neutrino disappearance with an off-axis neutrino beam with a peak energy of 0.6 GeV. Near detector measurements are used to constrain the neutrino flux and cross section parameters. The Su
per-Kamiokande far detector, which is 295 km downstream of the neutrino production target, collected data corresponding to $3.01 times 10^{20}$ protons on target. In the absence of neutrino oscillations, $205 pm 17$ (syst.) events are expected to be detected and only 58 muon neutrino event candidates are observed. A fit to the neutrino rate and energy spectrum assuming three neutrino flavors, normal mass hierarchy and $theta_{23}leq pi/4$ yields a best-fit mixing angle $sin^2(2theta_{23})=1.000$ and mass splitting $|Delta m^2_{32}| =2.44 times 10^{-3}$ eV$^2$/c$^4$. If $theta_{23}geq pi/4$ is assumed, the best-fit mixing angle changes to $sin^2(2theta_{23})=0.999$ and the mass splitting remains unchanged.
The T2K collaboration: reports evidence for electron neutrino appearance at the atmospheric mass splitting, |Delta m_{32}^2|=2.4x10^{-3} eV^2. An excess of electron neutrino interactions over background is observed from a muon neutrino beam with a pe
ak energy of 0.6 GeV at the Super-Kamiokande (SK) detector 295 km from the beams origin. Signal and background predictions are constrained by data from near detectors located 280 m from the neutrino production target. We observe 11 electron neutrino candidate events at the SK detector when a background of 3.3pm0.4(syst.) events is expected. The background-only hypothesis is rejected with a p-value of 0.0009 (3.1sigma), and a fit assuming u_{mu}-> u_e oscillations with sin^2(2theta_{23})=1, delta_{CP}=0 and |Delta m_{32}^2|=2.4x10^{-3} eV^2 yields sin^2(2theta_{13})=0.088^{+0.049}_{-0.039}(stat.+syst.).
T2K has performed the first measurement of u{mu} inclusive charged current interactions on carbon at neutrino energies of ~1 GeV where the measurement is reported as a flux-averaged double differential cross section in muon momentum and angle. The f
lux is predicted by the beam Monte Carlo and external data, including the results from the NA61/SHINE experiment. The data used for this measurement were taken in 2010 and 2011, with a total of 10.8 x 10^{19} protons-on-target. The analysis is performed on 4485 inclusive charged current interaction candidates selected in the most upstream fine-grained scintillator detector of the near detector. The flux-averaged total cross section is <sigma_CC>_phi =(6.91 +/- 0.13 (stat) +/- 0.84 (syst)) x10^{-39} cm^2/nucleon for a mean neutrino energy of 0.85 GeV.
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 detect
ors 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.
