Giles Barr

Abstract:

A measurement of the double-differential cross-section for the production of charged pions in proton-tantalum collisions emitted at large angles from the incoming beam direction is presented. The data were taken in 2002 with the HARP detector in the T9 beam line of the CERN PS. The pions were produced by proton beams in a momentum range from 3 GeV/c to 12 GeV/c hitting a tantalum target with a thickness of 5% of a nuclear interaction length. The angular and momentum range covered by the experiment (100 MeV/c ≤ p< 800 MeV/c and 0.35 rad ≤ θ< 2.15 rad) is of particular importance for the design of a neutrino factory. The produced particles were detected using a small-radius cylindrical time projection chamber (TPC) placed in a solenoidal magnet. Track recognition, momentum determination and particle identification were all performed based on the measurements made with the TPC. An elaborate system of detectors in the beam line ensured the identification of the incident particles. Results are shown for the double-differential cross-sections d 2σ/dpdθ at four incident proton beam momenta (3 GeV/c, 5 GeV/c, 8 GeV/c and 12 GeV/c). In addition, the pion yields within the acceptance of typical neutrino factory designs are shown as a function of beam momentum. The measurement of these yields within a single experiment eliminates most systematic errors in the comparison between rates at different beam momenta and between positive and negative pion production. © 2007 Springer-Verlag / Società Italiana di Fisica.

Abstract:

We found 140 neutrino-induced muons in 854.24 live days in the MINOS far detector, which has an acceptance for neutrino-induced muons of 6.91×106cm2sr. We looked for evidence of neutrino disappearance in this data set by computing the ratio of the number of low momentum muons to the sum of the number of high momentum and unknown momentum muons for both data and Monte Carlo expectation in the absence of neutrino oscillations. The ratio of data and Monte Carlo ratios, R, is R=0.65-0.12+0.15(stat)±0.09(syst), a result that is consistent with an oscillation signal. A fit to the data for the oscillation parameters sin 22θ23 and Δm232 excludes the null oscillation hypothesis at the 94% confidence level. We separated the muons into μ- and μ+ in both the data and Monte Carlo events and found the ratio of the total number of μ- to μ+ in both samples. The ratio of those ratios, R^CPT, is a test of CPT conservation. The result R^CPT=0.72-0.18+0.24(stat)-0. 04+0.08(syst) is consistent with CPT conservation. © 2007 The American Physical Society.

Abstract:

The beam and detector, used for the NA48 experiment, devoted to the measurement of Re (ε{lunate}′ / ε{lunate}), and for the NA48/1 experiment on rare KS and neutral hyperon decays, are described. © 2007 Elsevier B.V. All rights reserved.

Abstract:

This Letter reports on a new high precision measurement of the form factors of the KL → π± μ∓ νμ decay. The data sample of about 2.3 × 106 events was recorded in 1999 by the NA48 experiment at CERN. Studying the Dalitz plot density we measured a linear, λ+′ = (20.5 ± 2.2stat ± 2.4syst) × 10-3, and a quadratic, λ+″ = (2.6 ± 0.9stat ± 1.0syst) × 10-3 term in the power expansion of the vector form factor. No evidence was found for a second order term for the scalar form factor; the linear slope was determined to be λ0 = (9.5 ± 1.1stat ± 0.8syst) × 10-3. Using a linear fit our results were: λ+ = (26.7 ± 0.6stat ± 0.8syst) × 10-3 and λ0 = (11.7 ± 0.7stat ± 1.0syst) × 10-3. A pole fit of the form factors yields: mV = (905 ± 9stat ± 17syst)   MeV / c2 and mS = (1400 ± 46stat ± 53syst)   MeV / c2. © 2007 Elsevier B.V. All rights reserved.

Abstract:

The particle identification (PID) methods used for the calculation of secondary pion yields with the HARP forward spectrometer are presented. Information from time of flight and Cherenkov detectors is combined using likelihood techniques. The efficiencies and purities associated with the different PID selection criteria are obtained from the data. For the proton-aluminium interactions at 12.9 GeV/c incident momentum, the PID efficiencies for positive pions are 86 % in the momentum range below 2 GeV/c, 92 % between 2 and 3 GeV/c and 98 % in the momentum range above 3 GeV/c. The purity of the selection is better than 92 % for all momenta. Special emphasis has been put on understanding the main error sources. The final PID uncertainty on the pion yield is 3.3 %. © 2007 Elsevier B.V. All rights reserved.