Person:

Feldman, Gary

Results are reported from a search for active to sterile neutrino oscillations in the MINOS long-baseline experiment, based on the observation of neutral-current neutrino interactions, from an exposure to the NuMI neutrino beam of 7.07×10207.07×1020 protons on target. A total of 802 neutral-current event candidates is observed in the Far Detector, compared to an expected number of 754±28(stat.)±37(syst.)754±28(stat.)±37(syst.) for oscillations among three active flavors. The fraction fsfs of disappearing \numu that may transition to νsνs is found to be less than 22% at the 90% C.L.

We searched for a sidereal modulation in the MINOS far detector neutrino rate. Such a signal would be a consequence of Lorentz and CPT violation as described by the standard-model extension framework. It also would be the first detection of a perturbative effect to conventional neutrino mass oscillations. We found no evidence for this sidereal signature, and the upper limits placed on the magnitudes of the Lorentz and CPT violating coefficients describing the theory are an improvement by factors of 20–510 over the current best limits found by using the MINOS near detector.

We report measurements of oscillation parameters from νμ and ν⎯⎯μ disappearance using beam and atmospheric data from MINOS. The data comprise exposures of 10.71×1020 protons on target in the νμ-dominated beam, 3.36×1020 protons on target in the ν⎯⎯μ-enhanced beam, and 37.88 kton yr of atmospheric neutrinos. Assuming identical ν and ν⎯⎯ oscillation parameters, we measure |Δm2|=(2.41+0.09−0.10)×10−3  eV2 and sin2(2θ)=0.950+0.035−0.036. Allowing independent ν and ν⎯⎯ oscillations, we measure antineutrino parameters of |Δm⎯⎯⎯2|=(2.50+0.23−0.25)×10−3  eV2 and sin2(2θ⎯⎯)=0.97+0.03−0.08, with minimal change to the neutrino parameters.

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 8.2×1020 protons on the NuMI target at Fermilab, we find that 2sin2(θ23)sin2(2θ13)<0.12(0.20) at 90% confidence level for δ=0 and the normal (inverted) neutrino mass hierarchy, with a best-fit of 2sin2(θ23)sin2(2θ13)=0.041+0.047−0.031(0.079+0.071−0.053). The θ13=0 hypothesis is disfavored by the MINOS data at the 89% confidence level.

We report constraints on antineutrino oscillation parameters that were obtained by using the two MINOS detectors to measure the 7% muon antineutrino component of the NuMI neutrino beam. In the Far Detector, we select 130 events in the charged-current muon antineutrino sample, compared to a prediction of 136.4±11.7(stat)+10.2−8.9(syst) events under the assumption |Δm⎯⎯⎯2|=2.32×10−3  eV2, sin2(2θ⎯⎯)=1.0. Assuming no oscillations occur at the Near Detector baseline, a fit to the two-flavor oscillation approximation constrains |Δm⎯⎯⎯2|<3.37×10−3  eV2 at the 90% confidence level with sin2(2θ⎯⎯)=1.0.

This Letter reports the first direct observation of muon antineutrino disappearance. The MINOS experiment has taken data with an accelerator beam optimized for ν⎯⎯μ production, accumulating an exposure of 1.71×1020 protons on target. In the Far Detector, 97 charged current ν⎯⎯μ events are observed. The no-oscillation hypothesis predicts 156 events and is excluded at 6.3σ. The best fit to oscillation yields |Δm⎯⎯⎯2|=[3.36+0.46−0.40(stat)±0.06(syst)]×10−3  eV2, sin2(2θ⎯⎯)=0.86+0.11−0.12(stat)±0.01(syst). The MINOS νμ and ν⎯⎯μ measurements are consistent at the 2.0% confidence level, assuming identical underlying oscillation parameters.

We report new constraints on flavor-changing non-standard neutrino interactions from the MINOS experiment, in which neutrino versus antineutrino interactions can be distinguished on an event-by-event basis. We analyzed a combined set of beam neutrino and antineutrino data from the well-understood NuMI beam, and found no evidence for deviations from standard neutrino mixing. The observed energy spectra constrain the non-standard neutrino interactions parameter to the range −0.20<εμτ<0.07(90%C.L.).

The magnetized MINOS Near Detector, at a depth of 225 mwe, is used to measure the atmospheric muon charge ratio. The ratio of observed positive to negative atmospheric muon rates, using 301 days of data, is measured to be 1.266±0.001(stat)+0.015−0.014(syst). This measurement is consistent with previous results from other shallow underground detectors and is 0.108±0.019(stat+syst) lower than the measurement at the functionally identical MINOS Far Detector at a depth of 2070 mwe. This increase in charge ratio as a function of depth is consistent with an increase in the fraction of muons arising from kaon decay for increasing muon surface energies.

We report on a new analysis of neutrino oscillations in MINOS using the complete set of accelerator and atmospheric data. The analysis combines the νμ disappearance and νe appearance data using the three-flavor formalism. We measure |Δm232|=[2.28–2.46]×10−3  eV2 (68% C.L.) and sin2θ23=0.35–0.65 (90% C.L.) in the normal hierarchy, and |Δm232|=[2.32–2.53]×10−3  eV2 (68% C.L.) and sin2θ23=0.34–0.67 (90% C.L.) in the inverted hierarchy. The data also constrain δCP, the θ23 octant degeneracy and the mass hierarchy; we disfavor 36% (11%) of this three-parameter space at 68% (90%) C.L.

This paper reports results from a search for νμ→νe transitions by the MINOS experiment based on a 7×1020 protons-on-target exposure. Our observation of 54 candidate νe events in the far detector with a background of 49.1±7.0(stat)±2.7(syst) events predicted by the measurements in the near detector requires 2sin2(2θ13)sin2θ23<0.12(0.20) at the 90% C.L. for the normal (inverted) mass hierarchy at δCP=0. The experiment sets the tightest limits to date on the value of θ13 for nearly all values of δCP for the normal neutrino mass hierarchy and maximal sin2(2θ23).