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We present a search at the Jefferson Laboratory for new forces mediated by sub-GeV vector bosons with weak coupling α' to electrons. Such a particle A' can be produced in electron-nucleus fixed-target scattering and then decay to an e + e- pair, producing a narrow resonance in the QED trident spectrum. Using APEX test run data, we searched in the mass range 175-250 MeV, found no evidence for an A'→ e+ e- reaction, and set an upper limit of α'/α ~/= 10(-6). Our findings demonstrate that fixed-target searches can explore a new, wide, and important range of masses and couplings for sub-GeV forces.

The ProtoDUNE-SP detector is a single-phase liquid argon time projection chamber with an active volume of 7.2× 6.1× 7.0 m3. It is installed at the CERN Neutrino Platform in a specially-constructed beam that delivers charged pions, kaons, protons, muons and electrons with momenta in the range 0.3 GeV/c to 7 GeV/c. Beam line instrumentation provides accurate momentum measurements and particle identification. The ProtoDUNE-SP detector is a prototype for the first far detector module of the Deep Underground Neutrino Experiment, and it incorporates full-size components as designed for that module. This paper describes the beam line, the time projection chamber, the photon detectors, the cosmic-ray tagger, the signal processing and particle reconstruction. It presents the first results on ProtoDUNE-SP's performance, including noise and gain measurements, dE/dx calibration for muons, protons, pions and electrons, drift electron lifetime measurements, and photon detector noise, signal sensitivity and time resolution measurements. The measured values meet or exceed the specifications for the DUNE far detector, in several cases by large margins. ProtoDUNE-SP's successful operation starting in 2018 and its production of large samples of high-quality data demonstrate the effectiveness of the single-phase far detector design.

Kerth, L. et al.. (2012) Branching fraction and form-factor shape measurements of exclusive charmless semileptonic B decays, and determination of |V_{ub}|. Physical Review D (Particles, Fields, Gravitation and Cosmology), Vol.86 (No.9). Article no.092004 Permanent WRAP url: http://wrap.warwick.ac.uk/52210 Copyright and reuse:The Warwick Research Archive Portal (WRAP) makes the work of researchers of the University of Warwick available open access under the following conditions. Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.Copies of full items can be used for personal research or study, educational, or not-forprofit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. Publisher's statement: © 2012 American Physical Society A note on versions:The version presented here is a working paper or pre-print that may be later published elsewhere. If a published version is known of, the above WRAP url will contain details on finding it. We report the results of a study of the exclusive charmless semileptonic decays,undertaken with approximately 462 × 10 6 BB pairs collected at the Υ(4S) resonance with the BABAR detector. The analysis uses events in which the signal B decays are reconstructed with a loose neutrino reconstruction technique. We obtain partial branching fractions in several bins of q 2 , the square of the momentum transferred to the lepton-neutrino pair, for B 0 → π − ℓ + ν, B + → π 0 ℓ + ν, B + → ωℓ + ν and B + → ηℓ + ν. From these distributions, we extract the form-factor shapes f+(q 2 ) and the total branching fractions B(B 0 → π − ℓ + ν) = (1.45 ± 0.04stat ± 0.06syst) × 10 −4 (combined π − and π 0 decay channels assuming isospin symmetry), B(B + → ωℓ + ν) = (1.19 ± 0.16stat ± 0.09syst) × 10 −4and B(B + → ηℓ + ν) = (0.38 ± 0.05stat ± 0.05syst) × 10 −4 . We also measure B(B + → η ′ ℓ + ν) = (0.24 ± 0.08stat ± 0.03syst) × 10 −4 . We obtain values for the magnitude of the CKM matrix element |V ub | by direct comparison with three different QCD calculations in restricted q 2 ranges of B → πℓ + ν decays. From a simultaneous fit to the experimental data over the full q 2 range and the FNAL/MILC lattice QCD predictions, we obtain |V ub | = (3.25 ± 0.31) × 10 −3 , where the error is the combined experimental and theoretical uncertainty.