Showing papers by "Jim Napolitano published in 2015"

New Measurement of Antineutrino Oscillation with the Full Detector Configuration at Daya Bay

Abstract: We report a new measurement of electron antineutrino disappearance using the fully constructed Daya Bay Reactor Neutrino Experiment. The final two of eight antineutrino detectors were installed in the summer of 2012. Including the 404 days of data collected from October 2012 to November 2013 resulted in a total exposure of 6.9×10^5 GW_(th) ton days, a 3.6 times increase over our previous results. Improvements in energy calibration limited variations between detectors to 0.2%. Removal of six ^(241)Am−^(13)C radioactive calibration sources reduced the background by a factor of 2 for the detectors in the experimental hall furthest from the reactors. Direct prediction of the antineutrino signal in the far detectors based on the measurements in the near detectors explicitly minimized the dependence of the measurement on models of reactor antineutrino emission. The uncertainties in our estimates of sin 2^2θ_(13) and |Δm^2_(ee)| were halved as a result of these improvements. An analysis of the relative antineutrino rates and energy spectra between detectors gave sin^2 2θ_(13)=0.084±0.005 and |Δm^2_(ee)|=(2.42±0.11)×10^(−3) eV^2 in the three-neutrino framework.

The PROSPECT Physics Program

Abstract: The Precision Reactor Oscillation and Spectrum Experiment, PROSPECT, is designed to make a precise measurement of the antineutrino spectrum from a highly-enriched uranium reactor and probe eV-scale sterile neutrinos by searching for neutrino oscillations over meter-long distances. PROSPECT is conceived as a 2-phase experiment utilizing segmented $^6$Li-doped liquid scintillator detectors for both efficient detection of reactor antineutrinos through the inverse beta decay reaction and excellent background discrimination. PROSPECT Phase I consists of a movable 3-ton antineutrino detector at distances of 7 - 12 m from the reactor core. It will probe the best-fit point of the $ u_e$ disappearance experiments at 4$\sigma$ in 1 year and the favored region of the sterile neutrino parameter space at $>$3$\sigma$ in 3 years. With a second antineutrino detector at 15 - 19 m from the reactor, Phase II of PROSPECT can probe the entire allowed parameter space below 10 eV$^{2}$ at 5$\sigma$ in 3 additional years. The measurement of the reactor antineutrino spectrum and the search for short-baseline oscillations with PROSPECT will test the origin of the spectral deviations observed in recent $\theta_{13}$ experiments, search for sterile neutrinos, and conclusively address the hypothesis of sterile neutrinos as an explanation of the reactor anomaly.

The muon system of the Daya Bay Reactor antineutrino experiment

Abstract: The Daya Bay experiment consists of functionally identical antineutrino detectors immersed in pools of ultrapure water in three well-separated underground experimental halls near two nuclear reactor complexes. These pools serve both as shields against natural, low-energy radiation, and as water Cherenkov detectors that efficiently detect cosmic muons using arrays of photomultiplier tubes. Each pool is covered by a plane of resistive plate chambers as an additional means of detecting muons. Design, construction, operation, and performance of these muon detectors are described.

The veto system of the DarkSide-50 experiment

Abstract: Nuclear recoil events produced by neutron scatters form one of the most important classes of background in WIMP direct detection experiments, as they may produce nuclear recoils that look exactly like WIMP interactions. In DarkSide-50, we both actively suppress and measure the rate of neutron-induced background events using our neutron veto, composed of a boron-loaded liquid scintillator detector within a water Cherenkov detector. This paper is devoted to the description of the neutron veto system of DarkSide-50, including the detector structure, the fundamentals of event reconstruction and data analysis, and basic performance parameters.

Light collection and pulse-shape discrimination in elongated scintillator cells for the PROSPECT reactor antineutrino experiment

Abstract: Author(s): Ashenfelter, J; Balantekin, B; Band, HR; Barclay, G; Bass, CD; Berish, D; Bowden, NS; Bowes, A; Brodsky, JP; Bryan, CD; Cherwinka, JJ; Chu, R; Classen, T; Commeford, K; Davee, D; Dean, D; Deichert, G; Diwan, MV; Dolinski, MJ; Dolph, J; Dwyer, DA; Gaison, JK; Galindo-Uribarri, A; Gilje, K; Glenn, A; Goddard, BW; Green, M; Han, K; Hans, S; Heeger, KM; Heffron, B; Jaffe, DE; Langford, TJ; Littlejohn, BR; Caicedo, DAM; McKeown, RD; Mendenhall, MP; Mueller, P; Mumm, HP; Napolitano, J; Neilson, R; Norcini, D; Pushin, D; Qian, X; Romero, E; Rosero, R; Saldana, L; Seilhan, BS; Sharma, R; Sheets, S; Stemen, NT; Surukuchi, PT; Varner, RL; Viren, B; Wang, W; White, B; White, C; Wilhelmi, J; Williams, C; Wise, T; Yao, H; Yeh, M; Yen, YR; Zangakis, G; Zhang, C; Zhang, X | Abstract: A meter-long, 23-liter EJ-309 liquid scintillator detector has been constructed to study the light collection and pulse-shape discrimination performance of elongated scintillator cells for the PROSPECT reactor antineutrino experiment. The magnitude and uniformity of light collection and neutron-gamma discrimination power in the energy range of antineutrino inverse beta decay products have been studied using gamma and spontaneous fission calibration sources deployed along the cell axis. We also study neutron-gamma discrimination and light collection abilities for differing PMT and reflector configurations. Key design features for optimizing MeV-scale response and background rejection capabilities are identified.

Light Collection and Pulse-Shape Discrimination in Elongated Scintillator Cells for the PROSPECT Reactor Antineutrino Experiment

Abstract: A meter-long, 23-liter EJ-309 liquid scintillator detector has been constructed to study the light collection and pulse-shape discrimination performance of elongated scintillator cells for the PROSPECT reactor antineutrino experiment. The magnitude and uniformity of light collection and neutron/gamma discrimination power in the energy range of antineutrino inverse beta decay products have been studied using gamma and spontaneous fission calibration sources deployed along the cell long axis. We also study neutron-gamma discrimination and light collection abilities for differing PMT and reflector configurations. Key design features for optimizing MeV-scale response and background rejection capabilities are identified.

The Water Purification System for the Daya Bay Reactor Neutrino Experiment

Abstract: We describe the design, installation, and operation of a purification system that is able to provide large volumes of high purity ASTM (D1193-91) Type-I water to a high energy physics experiment. The water environment is underground in a lightly sealed system, and this provides significant challenges to maintaining high purity in the storage pools, each of which contains several thousand cubic meters. High purity is dictated by the need for large optical absorption length, which is critical for the operation of the experiment. The system is largely successful, and the water clarity criteria are met. We also include a discussion of lessons learned.

Waterproofed photomultiplier tube assemblies for the Daya Bay reactor neutrino experiment

Abstract: In the Daya Bay Reactor Neutrino Experiment 960 20-cm-diameter waterproof photomultiplier tubes are used to instrument three water pools as Cherenkov detectors for detecting cosmic ray muons. Of these 960 photomultiplier tubes, 341 are recycled from the MACRO experiment. A systematic program was undertaken to refurbish them as waterproof assemblies. In the context of passing the water leakage check, a success rate better than 97% was achieved. Details of the design, fabrication, testing, operation, and performance of these waterproofed photomultiplier-tube assemblies are presented. (C) 2015 Elsevier B.V. All rights reserved.