T2K (Tokai to Kamioka) is a long baseline neutrino experiment with the primary goal of measuring the neutrino mixing angle θ 13 . It uses a muon neutrino beam, produced at the J-PARC accelerator facility in Tokai, sent through a near detector complex on its way to the far detector, Super-Kamiokande. Appearance of electron neutrinos at the far detector due to oscillation is used to measure the value of θ 13 .

The T2K experiment is a long baseline neutrino oscillation experiment. Its main goal is to measure the last unknown lepton sector mixing angle θ13θ13 by observing νeνe appearance in a νμνμ beam. It also aims to make a precision measurement of the known oscillation parameters, View the MathML sourceΔm232 and sin22θ23sin22θ23, via νμνμ disappearance studies. Other goals of the experiment include various neutrino cross-section measurements and sterile neutrino searches. The experiment uses an intense proton beam generated by the J-PARC accelerator in Tokai, Japan, and is composed of a neutrino beamline, a near detector complex (ND280), and a far detector (Super-Kamiokande) located 295 km away from J-PARC. This paper provides a comprehensive review of the instrumentation aspect of the T2K experiment and a summary of the vital information for each subsystem

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 intervals for the two possible mass hierarchies: normal hierarchy∶ sin 2 θ 23 ¼ 0.514 þ0.055 −0.056 and Δm 2 32 ¼ ð2.51 AE 0.10Þ × 10 −3 eV 2 =c 4 and inverted hierarchy∶ sin 2 θ 23 ¼ 0.511 AE 0.055 and Δm 2 13 ¼ ð2.48 AE 0.10Þ × 10 −3 eV 2 =c 4 . The analysis accounts for multinucleon 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, jΔm 2 j, sin 2 θ 23 , sin 2 θ 13 , δ CP , 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 δ CP ¼ ½0.15; 0.83 π for normal hierarchy and δ CP ¼ ½−0.08; 1.09 π 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% one-dimensional credible intervals for the other oscillation parameters, when reactor data are included, are sin 2 θ 23 ¼ 0.528 þ0.055 −0.038 and jΔm 2 32 j ¼ ð2.51 AE 0.11Þ × 10 −3 eV 2 =c 4 .

The T2K experiment has observed electron neutrino appearance in a muon neutrino beam produced 295 km from the Super-Kamiokande detector with a peak energy of 0.6 GeV. A total of 28 electron neutrino events were detected with an energy distribution consistent with an appearance signal, PRL 112, 061802 (2014) P H Y S I C A L R E V I E W L E T T E R Sweek ending 14 FEBRUARY 2014 061802-2 corresponding to a significance of 7.3σ when compared to 4.92 AE 0.55 expected background events. In the Pontecorvo-Maki-Nakagawa-Sakata mixing model, the electron neutrino appearance signal depends on several parameters including three mixing angles θ 12 , θ 23 , θ 13 , a mass difference Δm 2 32 and a CP violating phase δ CP . In this neutrino oscillation scenario, assuming jΔm 2 32 j ¼ 2.4 × 10 −3 eV 2 , sin 2 θ 23 ¼ 0.5, and Δm −0.037 ) is obtained at δ CP ¼ 0. When combining the result with the current best knowledge of oscillation parameters including the world average value of θ 13 from reactor experiments, some values of δ CP are disfavored at the 90% C.L. DOI: 10.1103/PhysRevLett.112.061802 PACS numbers: 14.60.Pq, 14.60.Lm, 25.30.Pt, 29.40.Ka Introduction.-The discovery of neutrino oscillations using atmospheric neutrinos was made by SuperKamiokande in 1998 [1]. Since then, many other experiments have confirmed the phenomenon of neutrino oscillations through various disappearance modes of flavor transformations. However, to date, there has not been an observation of the explicit appearance of a different neutrino flavor from neutrinos of another flavor through neutrino oscillations. In 2011, the T2K collaboration published the first indication of electron neutrino appearance from a muon neutrino beam at 2.5σ significance based on a data set corresponding to 1.43 × 10 20 protons on target (POT) [2,3]. This result was followed by the publication of further evidence for electron neutrino appearance at 3.1σ in early 2013 [4]. This Letter presents new results from the T2K experiment that establish, at greater than 5σ, the observation of electron-neutrino appearance from a muon-neutrino beam.In a three-flavor framework, neutrino oscillations are described by the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix [5,6] which is parametrized by three mixing angles θ 12 , θ 23 , θ 13 , and a CP violating phase δ CP . In this framework, the probability for ν μ → ν e oscillation can be expressed [7] as where L is the neutrino propagation distance and E is the neutrino energy. The measurement of ν μ → ν e oscillations is of particular interest because this mode is sensitive to both θ 13 and δ CP . The first indication of nonzero θ 13 was published by T2K [3] based on the measurement of ν μ → ν e oscillations. More recently, indications of ν μ → ν e oscillations were also reported by the MINOS experiment [8]. The value of θ 13 is now precisely known to be 9.1°AE 0.6°from measurements ofν e disappearance in reactor neutrino experiments [9][10][11][12]. Using the reactor measurement of θ 13 , the ν μ → ν e appearance mode can be used to ...

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.

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The ProtoDUNE-SP detector is a single-phase liquid argon time projection chamber with an active volume of 7.2× 6.1× 7.0 m3. It is installed at the CERN Neutrino Platform in a specially-constructed beam that delivers charged pions, kaons, protons, muons and electrons with momenta in the range 0.3 GeV/c to 7 GeV/c. Beam line instrumentation provides accurate momentum measurements and particle identification. The ProtoDUNE-SP detector is a prototype for the first far detector module of the Deep Underground Neutrino Experiment, and it incorporates full-size components as designed for that module. This paper describes the beam line, the time projection chamber, the photon detectors, the cosmic-ray tagger, the signal processing and particle reconstruction. It presents the first results on ProtoDUNE-SP's performance, including noise and gain measurements, dE/dx calibration for muons, protons, pions and electrons, drift electron lifetime measurements, and photon detector noise, signal sensitivity and time resolution measurements. The measured values meet or exceed the specifications for the DUNE far detector, in several cases by large margins. ProtoDUNE-SP's successful operation starting in 2018 and its production of large samples of high-quality data demonstrate the effectiveness of the single-phase far detector design.

Two different nuclear-medium effects are isolated using a low three-momentum transfer subsample of neutrino-carbon scattering data from the MINERvA neutrino experiment. The observed hadronic energy in charged-current νµ interactions is combined with muon kinematics to permit separation of the quasielastic and ∆(1232) resonance processes. First, we observe a small cross section at very low energy transfer that matches the expected screening effect of long-range nucleon correlations. Second, additions to the event rate in the kinematic region between the quasielastic and ∆ resonance processes are needed to describe the data. The data in this kinematic region also has an enhanced population of multi-proton final states. Contributions predicted for scattering from a nucleon pair have both properties; the model tested in this analysis is a significant improvement but does not fully describe the data. We present the results as a double-differential cross section to enable further investigation of nuclear models. Improved description of the effects of the nuclear environment are required by current and future neutrino oscillation experiments.