Physical Review Letters 108 (2012)
We report an improved measurement of ν ̄μ disappearance over a distance of 735 km using the MINOS detectors and the Fermilab Main Injector neutrino beam in a ν ̄μ-enhanced configuration. From a total exposure of 2.95×1020 protons on target, of which 42% have not been previously analyzed, we make the most precise measurement of Δm ̄2=[2.62-0.28+0.31(stat)±0. 09(syst)]×10 -3eV2 and constrain the ν ̄μ mixing angle sin2(2θ̄)>0.75 (90% C.L.). These values are in agreement with Δm2 and sin2(2θ) measured for ν μ, removing the tension reported in. © 2012 American Physical Society.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 694 (2012) 211-223
Precise measurement of neutrino beam direction and intensity was achieved based on a new concept with modularized neutrino detectors. INGRID (Interactive Neutrino GRID) is an on-axis near detector for the T2K long baseline neutrino oscillation experiment. INGRID consists of 16 identical modules arranged in horizontal and vertical arrays around the beam center. The module has a sandwich structure of iron target plates and scintillator trackers. INGRID directly monitors the muon neutrino beam profile center and intensity using the number of observed neutrino events in each module. The neutrino beam direction is measured with accuracy better than 0.4 mrad from the measured profile center. The normalized event rate is measured with 4% precision. © 2012 Elsevier B.V. All rights reserved.
Physical Review D - Particles, Fields, Gravitation and Cosmology 85 (2012)
We report a measurement of muon-neutrino disappearance in the T2K experiment. The 295-km muon-neutrino beam from Tokai to Kamioka is the first implementation of the off-axis technique in a long-baseline neutrino oscillation experiment. With data corresponding to 1.43×1020 protons on target, we observe 31 fully-contained single μ-like ring events in Super-Kamiokande, compared with an expectation of 104±14(syst) events without neutrino oscillations. The best-fit point for two-flavor ν μ→ν τ oscillations is sin2(2θ 23)=0.98 and |Δm322|=2.65×10 -3eV2. The boundary of the 90% confidence region includes the points ( sin2(2θ 23), |Δm322|)=(1.0,3.1×10 -3eV2), (0.84, 2.65×10 -3eV2) and (1.0, 2.2×10 -3eV2). © 2012 American Physical Society.
PHYSICAL REVIEW D 85 (2012) ARTN 031103
New measurements of the transverse beam asymmetry for elastic electron scattering from selected nuclei
Physical Review Letters 109 (2012)
We have measured the beam-normal single-spin asymmetry A n in the elastic scattering of 1-3 GeV transversely polarized electrons from H1 and for the first time from He4, C12, and Pb208. For H1, He4, and C12, the measurements are in agreement with calculations that relate A n to the imaginary part of the two-photon exchange amplitude including inelastic intermediate states. Surprisingly, the Pb208 result is significantly smaller than the corresponding prediction using the same formalism. These results suggest that a systematic set of new A n measurements might emerge as a new and sensitive probe of the structure of heavy nuclei. © 2012 American Physical Society.
Physical Review D - Particles, Fields, Gravitation and Cosmology 86 (2012)
This paper reports measurements of atmospheric neutrino and antineutrino interactions in the MINOS Far Detector, based on 2553 live-days (37.9kton-years) of data. A total of 2072 candidate events are observed. These are separated into 905 contained-vertex muons and 466 neutrino-induced rock-muons, both produced by charged-current ν μ and ν ̄μ interactions, and 701 contained-vertex showers, composed mainly of charged-current ν e and ν ̄e interactions and neutral-current interactions. The curvature of muon tracks in the magnetic field of the MINOS Far Detector is used to select separate samples of ν μ and ν ̄μ events. The observed ratio of ν ̄μ to ν μ events is compared with the MonteCarlo (MC) simulation, giving a double ratio of Rν̄/νdata/ Rν̄/νMC=1.03±0.08(stat)±0.08(syst). The ν μ and ν ̄μ data are separated into bins of L/E resolution, based on the reconstructed energy and direction of each event, and a maximum likelihood fit to the observed L/E distributions is used to determine the atmospheric neutrino oscillation parameters. This fit returns 90% confidence limits of |Δm2|=(1.9±0.4)×10 -3eV2 and sin22θ>0.86. The fit is extended to incorporate separate ν μ and ν ̄μ oscillation parameters, returning 90% confidence limits of |Δm2|-|Δm ̄2|=0.6- 0.8+2.4×10 -3eV2 on the difference between the squared-mass splittings for neutrinos and antineutrinos. © 2012 American Physical Society.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 686 (2012) 48-63
The pi-zero detector (POD) is one of the subdetectors that makes up the off-axis near detector for the Tokai-to-Kamioka (T2K) long baseline neutrino experiment. The primary goal for the POD is to measure the relevant cross-sections for neutrino interactions that generate π0s, especially the cross-section for neutral current π0 interactions, which are one of the dominant sources of background to the νμ→ νe appearance signal in T2K. The POD is composed of layers of plastic scintillator alternating with water bags and brass sheets or lead sheets and is one of the first detectors to use Multi-Pixel Photon Counters (MPPCs) on a large scale. © 2012 Elsevier B.V. All rights reserved.
44th Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting 2012 (2012) 99-117
In the context of time-of-flight measurements, the timing at the departure and arrival locations is obviously critical to the outcome of the experiment. In the case of neutrino time-of-flight experiments, the locations are many hundreds of kilometers apart with synchronization requirements of nanoseconds for several months at a time. In addition to the already stringent set of requirements outlined above, the locations of the origin of the particle beam and the detector need to be precisely determined. NIST and USNO have provided the MINOS (Main Injector Neutrino Oscillation Search) collaboration with both hardware and expertise to synchronize the two sites of the experiment, the accelerator at Fermilab in Batavia, IL and the Soudan Mine in northern Minnesota. Two GPS receivers are installed at each location where the local clocks are commercial Cesium clocks. Two more GPS receivers are constantly traveling between locations (including NIST in Boulder, CO) to provide multiple differential calibrations of the fixed receivers. The availability of the TWTFST equipment from USNO allowed for one comparison between the GPS and TWSTFT for the link between the locations, providing an independent means of determining the accuracy of the synchronization. Several months of continuous GPS data are now available, including the two-way calibration instance and several differential GPS calibrations. The results of data processing yielded synchronization stability below one nanosecond with accuracy at the nanosecond level over several months. © (2012) by the Institute of Navigation. All rights reserved.
Physical Review D - Particles, Fields, Gravitation and Cosmology 85 (2012)
We have searched for sidereal variations in the rate of antineutrino interactions in the MINOS Near Detector. Using antineutrinos produced by the NuMI beam, we find no statistically significant sidereal modulation in the rate. When this result is placed in the context of the Standard Model Extension theory we are able to place upper limits on the coefficients defining the theory. These limits are used in combination with the results from an earlier analysis of MINOS neutrino data to further constrain the coefficients. © 2012 American Physical Society.
PHYSICAL REVIEW D 85 (2012) ARTN 031101
New Journal of Physics 14 (2012)
In this paper we describe how two or more experimental results can be combined within the procedure of Feldman and Cousins, to provide combined confidence limits on the physical parameters of interest. We demonstrate the technique by combining the recent electron neutrino appearance results from T2K and MINOS. Our best fit point is sin 2 2θ 13 = 0.08 (0.11) and δ = 1.1 (2.0)π; in addition we exclude sin2 2θ 13 = 0 at 2.7σ (2.8σ) for the normal (inverted) neutrino mass hierarchy. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
Phys Rev Lett 107 (2011) 181802-
We report the results of a search for ν(e) appearance in a ν(μ) 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) (θ(23))sin(2)(2θ(13))<0.12(0.20) at 90% confidence level for δ = 0 and the normal (inverted) neutrino mass hierarchy, with a best-fit of 2sin(2) (θ(23))sin(2)(2θ(13)) = 0.041(-0.031)(+0.047) (0.079(-0.053) (+0.071)). The θ(13) = 0 hypothesis is disfavored by the MINOS data at the 89% confidence level.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment (2011)
IEEE Transactions on Nuclear Science 58 (2011) 1800-1806
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.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 659 (2011) 106-135
The T2K experiment is a long baseline neutrino oscillation experiment. Its main goal is to measure the last unknown lepton sector mixing angle θ13 by observing νe appearance in a νμ beam. It also aims to make a precision measurement of the known oscillation parameters, Δ232+ and sin22θ23, via νμ 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. © 2011 Elsevier B.V. All rights reserved.
Physical Review Letters 107 (2011)
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.
Nuclear Physics B - Proceedings Supplements 217 (2011) 169-174
The goal of the Tokai-to-Kamioka (T2K) experiment is to search for the neutrino oscillation parameter θ13 and determine precisely the value of θ23 and Δmθ232. In this proceeding we describe the T2K baseline and detector systems. We report the performance and stability of the different component during the first run covering the period from January to June 2010. Next year expectation for θ13 sensitivity is also presented. © 2011 Elsevier B.V.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 656 (2011) 69-83
The calorimeter, range detector and active target elements of the T2K near detectors rely on the Hamamatsu Photonics Multi-Pixel Photon Counters (MPPCs) to detect scintillation light produced by charged particles. Detailed measurements of the MPPC gain, afterpulsing, crosstalk, dark noise, and photon detection efficiency for low light levels are reported. In order to account for the impact of the MPPC behavior on T2K physics observables, a simulation program has been developed based on these measurements. The simulation is used to predict the energy resolution of the detector. Copyright © 2011 Published by Elsevier B.V. All rights reserved.
Physical Review Letters 107 (2011)
This Letter reports the first direct observation of muon antineutrino disappearance. The MINOS experiment has taken data with an accelerator beam optimized for ν̄μ production, accumulating an exposure of 1.71×1020 protons on target. In the Far Detector, 97 charged current ν̄μ events are observed. The no-oscillation hypothesis predicts 156 events and is excluded at 6.3σ. The best fit to oscillation yields |Δm⊃̄2|=[3.36-0.40+0.46(stat)±0.06(syst)] ×10⊃-3eV2, ⊃sin⊃2(2θ̄)=0.86-0.12+0.11(stat) ±0.01(syst). The MINOS νμ and ν̄μ measurements are consistent at the 2.0% confidence level, assuming identical underlying oscillation parameters. © 2011 American Physical Society.