Giles Barr

Abstract:

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)-8.9+10.2(syst) events under the assumption |Δm̄2|=2.32×10-3eV2, sin2(2θ̄)=1.0. Assuming no oscillations occur at the Near Detector baseline, a fit to the two-flavor oscillation approximation constrains |Δm̄2|<3.37×10-3eV2 at the 90% confidence level with sin2(2θ̄)=1.0. © 2011 American Physical Society.

Abstract:

T2K is a second generation long-baseline experiment in Japan, designed to perform precision studies of neutrino oscillations. A neutrino beam originating at the J-PARC facility is sampled by two near detectors, approximately 280 m distant from the source and directed towards the Kamioka underground facility, 295 km distant, where the Super-Kamiokande water Cerenkov detector is situated. Both the on-axis (INGRID) and off-axis (ND280) near detectors employ the MIDAS framework for their data acquisition systems. Events are selected via a flexible hardware trigger, which allows mixed operating modes incorporating beam spill, cosmic and calibration triggers. Data are acquired from the front-end electronics over optical Gigabit Ethernet links by custom MIDAS front-end applications distributed over a cluster of Linux computers. Event fragments from all sub-detectors are merged and logged on a central backend processor and then copied to remote storage for long-term archival. The system is also designed to allow flexible partitioning of sub-detectors for standalone diagnostics and calibration. We present the design of the DAQ system and report on experience gathered during early operation of the near detectors. © 2006 IEEE.

Abstract:

The T2K experiment observes indications of νμ→ν e appearance in data accumulated with 1.43×1020 protons on target. Six events pass all selection criteria at the far detector. In a three-flavor neutrino oscillation scenario with |Δm232|=2.4×10⊃- 3eV2, ⊃sin⊃ 22θ23=1 and ⊃sin⊃ 22θ13=0, the expected number of such events is 1.5±0.3(syst). Under this hypothesis, the probability to observe six or more candidate events is 7×10⊃-3, equivalent to 2.5σ significance. At 90% C.L., the data are consistent with 0.03(0.04) <⊃sin⊃ 22θ13<0.28(0.34) for δCP= 0 and a normal (inverted) hierarchy.

Abstract:

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 |Δm²| = [3.36(-0.40)(+0.46)(stat) ± 0.06(syst)] × 10⁻³ eV², sin²(2θ) = 0.86(-0.12)(+0.11)(stat) ± 0.01(syst). The MINOS ν(μ) and ν(μ) measurements are consistent at the 2.0% confidence level, assuming identical underlying oscillation parameters.

Abstract:

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 7.07×10(20) 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) for oscillations among three active flavors. The fraction f(s) of disappearing ν(μ) that may transition to ν(s) is found to be less than 22% at the 90% C.L.