We report the results of a search for νe appearance in a νµ beam in the MINOS long-baseline neutrino experiment. With an improved analysis and an increased exposure of 8.2 × 10 20 protons on the NuMI target at Fermilab, we find that 2 sin 2 (θ23) sin 2 (2θ13) < 0.12 (0.20) at 90% confidence level for δ=0 and the normal (inverted) neutrino mass hierarchy, with a best fit of 2 sin 2 (θ23) sin 2 (2θ13) = 0.041−0.031 (0.079−0.053 ). The θ13=0 hypothesis is disfavored by the MINOS data at the 89% confidence level.PACS numbers: 14.60. Pq, 14.60.Lm, arXiv:1108.0015v1 [hep-ex] 29 Jul 2011 2 It has been experimentally established that neutrinos undergo flavor change as they propagate [1][2][3][4][5][6][7]. This phenomenon is well-described by three-flavor neutrino oscillations, characterized by the spectrum of neutrino masses together with the elements of the PMNS mixing matrix [8]. This matrix is often parametrized by three Euler angles θ ij and a CP-violating phase δ. While θ 12 and θ 23 are known to be large [1,4,6], θ 13 appears to be relatively small [9][10][11][12][13], with the tightest limits so far coming from the CHOOZ [10] and MINOS [12] experiments. The T2K collaboration has recently reported indications of a nonzero value for θ 13 at the 2.5σ confidence level (C.L.) [14]. This letter reports new θ 13 constraints from the MINOS experiment, using an increased data set and significant improvements to the analysis.MINOS is a two-detector long-baseline neutrino oscillation experiment situated along the NuMI neutrino beamline [15]. The 0.98-kton Near Detector (ND) is located on-site at Fermilab, 1.04 km downstream of the NuMI target. The 5.4-kton Far Detector (FD) is located 735 km downstream in the Soudan Underground Laboratory. The two detectors have nearly identical designs, each consisting of alternating layers of steel (2.54 cm thick) and plastic scintillator (1 cm). The scintillator layers are constructed from optically isolated, 4.1 cm wide strips that serve as the active elements of the detectors. The strips are read out via optical fibers and multi-anode photomultiplier tubes. Details can be found in Ref. [16].The data used in this analysis come from an exposure of 8.2×1020 protons on the NuMI target. The corresponding neutrino events in the ND have an energy spectrum that peaks at 3 GeV and a flavor composition of 91.7% ν µ , 7.0% ν µ , and 1.3% ν e +ν e , as estimated by beamline and detector Monte Carlo (MC) simulations, with additional constraints from MINOS ND data and external measurements [6,17]. The two-detector arrangement and the relatively small intrinsic ν e component make this analysis rather insensitive to beam uncertainties. Neutrino-nucleus and final-state interactions are simulated using NEUGEN3 [18], and particle propagation and detector response are simulated with GEANT3 [19].MINOS is sensitive to θ 13 through ν µ → ν e oscillations. To leading order, the probability for this oscillation mode is given bywhere ∆m 2 32 (in units of eV 2 ) and θ 23 are the dominant atmospheric oscillation...

and comprise 7.482 × 10 20 protons on target in neutrino mode, which yielded in the far detector 32 e-like and 135 μ-like events, and 7.471 × 10 20 protons on target in antineutrino mode, which yielded 4 e-like and 66 μ-like events. Reactor measurements of sin 2 2θ 13 have been used as an additional constraint. The one-dimensional confidence interval at 90% for the phase δ CP spans the range (−3.13, −0.39) for normal mass ordering. The CP conservation hypothesis (δ CP ¼ 0, π) is excluded at 90% C.L.

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 .

No abstract

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 ...