Giles Barr

Abstract:

This paper reports results from a search for νμ→ν e 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 2 sin2(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(2θ 23). © 2010 The American Physical Society.

Abstract:

A search for depletion of the combined flux of active neutrino species over a 735 km baseline is reported using neutral-current interaction data recorded by the MINOS detectors in the NuMI neutrino beam. Such a depletion is not expected according to conventional interpretations of neutrino oscillation data involving the three known neutrino flavors. A depletion would be a signature of oscillations or decay to postulated noninteracting sterile neutrinos, scenarios not ruled out by existing data. From an exposure of 3.18×1020 protons on target in which neutrinos of energies between ∼500MeV and 120 GeV are produced predominantly as νμ, the visible energy spectrum of candidate neutral-current reactions in the MINOS far detector is reconstructed. Comparison of this spectrum to that inferred from a similarly selected near-detector sample shows that of the portion of the νμ flux observed to disappear in charged-current interaction data, the fraction that could be converting to a sterile state is less than 52% at 90% confidence level (C.L.). The hypothesis that active neutrinos mix with a single sterile neutrino via oscillations is tested by fitting the data to various models. In the particular four-neutrino models considered, the mixing angles θ24 and θ34 are constrained to be less than 11° and 56° at 90% C.L., respectively. The possibility that active neutrinos may decay to sterile neutrinos is also investigated. Pure neutrino decay without oscillations is ruled out at 5.4 standard deviations. For the scenario in which active neutrinos decay into sterile states concurrently with neutrino oscillations, a lower limit is established for the neutrino decay lifetime τ3/m3>2.1×10-12s/eV at 90% C.L. © 2010 The American Physical Society.

Abstract:

The temperature of the upper atmosphere affects the height of primary cosmic ray interactions and the production of high-energy cosmic ray muons which can be detected deep underground. The MINOS far detector at Soudan, MN, has collected over 67×106 cosmic ray induced muons. The underground muon rate measured over a period of five years exhibits a 4% peak-to-peak seasonal variation which is highly correlated with the temperature in the upper atmosphere. The coefficient, αT, relating changes in the muon rate to changes in atmospheric temperature was found to be αT=0.873±0. 009(stat)±0.010(syst). Pions and kaons in the primary hadronic interactions of cosmic rays in the atmosphere contribute differently to αT due to the different masses and lifetimes. This allows the measured value of αT to be interpreted as a measurement of the K/π ratio for Ep 7TeV of 0.12-0.05+0.07, consistent with the expectation from collider experiments. © 2010 The American Physical Society.

Abstract:

Measurements of the double-differential proton production cross-section d2σ/dpdΩ in the range of momentum 0.5 GeV/c p ≤ 8.0 GeV/c and angle 0.05 rad ≤ θ < 0.25 rad in collisions of charged pions and protons on beryllium, carbon, aluminium, copper, tin, tantalum, and lead are presented. The data were taken with the large acceptance HARP detector in the T9 beam line of the CERN Proton Synchrotron. Incident particles were identified by an elaborate system of beam detectors and impinged on a target of 5% of a nuclear interaction length. The tracking and identification of the produced particles was performed using the forward spectrometer of the HARP experiment. Results are obtained for the double-differential cross-sections mainly at four incident beam momenta (3, 5, 8, and 12 GeV/c). Measurements are compared with predictions of the GEANT4 and MARS Monte Carlo generators. © 2010 The American Physical Society.