Improved Search for Muon-Neutrino to Electron-Neutrino Oscillations in MINOS

Abstract

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...

Predicting θ 13 and the neutrino mass scale from quark lepton mass hierarchies

“…In the following we shall employ Monte-Carlo techniques to study quantitatively the dependence of yet undetermined, but soon testable parameters of the neutrino sector on the unknown O(1) factors of the mass matrices. Using the already measured neutrino masses and mixings as input, we find surprisingly sharp predictions which indicate a large value for the smallest mixing angle θ 13 in accordance with recent results from T2K [13], Minos [14] and Double Chooz [15], a value for the lightest neutrino mass of O(10 −3 ) eV and one Majorana phase in the mixing matrix peaked at α 21 = π.…”

“…Of the three angles, two are only bounded from one side by experiment: for the largest mixing angle θ 23 there exists a lower bound, whereas the smallest mixing angle θ 13 is so far only bounded from above. Recent results from T2K [13], Minos [14] JHEP03(2012)008 and the preliminary result of Double Chooz [15] point to a value of θ 13 just below the current experimental bound. The respective best fit points, assuming a normal hierarchy, are sin 2 2θ 13 = 0. the corresponding distributions are shown in figure 1.…”

Study of lepton flavor violation in flavor symmetric models for lepton sector

“…As long as tan β is rather small, the deviation would be tiny but the large tan β scenario may be also fascinating because of the discrepancy of (g − 2) µ . Furthermore, nonzero θ 13 is confirmed at the experiments [17][18][19][20][21][22], so it is important to discuss the contribution of the T -breaking terms to the PMNS matrix. In the next section, we investigate the mass mixing from the one-loop correction, and discuss the contribution to θ 13 and the flavor changing processes.…”

“…Especially, we could find so many models motivated by the large mixing in neutrino sector, because the experimental result may imply so-called Tri-Bi maximal mixing [5][6][7], which can be easily accommodated by the BSMs with non-Abelian discrete flavor symmetry such as A 4 [8][9][10][11][12], S 4 [13][14][15], and ∆ (27) [16] etc.. Recent result on the nonzero θ 13 [17][18][19][20][21][22] may require some small modifications in those models, but we could expect that so many kinds of flavor symmetric models can be still consistent with the experimental results [4,. Then, the next question in this approach to the flavor structure would be how to test the flavor symmetry in experiments.…”

SUSY SU(5)×S 4 GUT flavor model for fermion masses and mixings with adjoint, large θ 13 PMNS

“…Even before the Daya Bay result, however, there have emerged direct evidence of large θ 13 from T2K [54], MINOS [55] and Double Chooz [56]. The accurate nonzero reactor angle θ 13 implies Tri-Bimaximal mixing pattern and else would be ruled out.…”