Showing papers by "Jim Napolitano published in 2016"

Measurement of the Reactor Antineutrino Flux and Spectrum at Daya Bay

Abstract: This Letter reports a measurement of the flux and energy spectrum of electron antineutrinos from six 2.9 GWth nuclear reactors with six detectors deployed in two near (effective baselines 512 and 561 m) and one far (1579 m) underground experimental halls in the Daya Bay experiment. Using 217 days of data, 296 721 and 41 589 inverse β decay (IBD) candidates were detected in the near and far halls, respectively. The measured IBD yield is (1.55±0.04) ×10(-18) cm(2) GW(-1) day(-1) or (5.92±0.14) ×10(-43) cm(2) fission(-1). This flux measurement is consistent with previous short-baseline reactor antineutrino experiments and is 0.946±0.022 (0.991±0.023) relative to the flux predicted with the Huber-Mueller (ILL-Vogel) fissile antineutrino model. The measured IBD positron energy spectrum deviates from both spectral predictions by more than 2σ over the full energy range with a local significance of up to ∼4σ between 4-6 MeV. A reactor antineutrino spectrum of IBD reactions is extracted from the measured positron energy spectrum for model-independent predictions.

Results from the first use of low radioactivity argon in a dark matter search

Abstract: Liquid argon is a bright scintillator with potent particle identification properties, making it an attractive target for direct-detection dark matter searches. The DarkSide-50 dark matter search here reports the first WIMP search results obtained using a target of low-radioactivity argon. DarkSide-50 is a dark matter detector, using two-phase liquid argon time projection chamber, located at the Laboratori Nazionali del Gran Sasso. The underground argon is shown to contain Ar-39 at a level reduced by a factor (1.4 +- 0.2) x 103 relative to atmospheric argon. We report a background-free null result from (2616 +- 43) kg d of data, accumulated over 70.9 live-days. When combined with our previous search using an atmospheric argon, the 90 % C.L. upper limit on the WIMP-nucleon spin-independent cross section based on zero events found in the WIMP search regions, is 2.0 x 10-44 cm2 (8.6 x 10-44 cm2, 8.0 x 10-43 cm2) for a WIMP mass of 100 GeV/c2 (1 TeV/c2 , 10 TeV/c2).

Improved Search for a Light Sterile Neutrino with the Full Configuration of the Daya Bay Experiment.

Abstract: This Letter reports an improved search for light sterile neutrino mixing in the electron antineutrino disappearance channel with the full configuration of the Daya Bay Reactor Neutrino Experiment. With an additional 404 days of data collected in eight antineutrino detectors, this search benefits from 3.6 times the statistics available to the previous publication, as well as from improvements in energy calibration and background reduction. A relative comparison of the rate and energy spectrum of reactor antineutrinos in the three experimental halls yields no evidence of sterile neutrino mixing in the 2 × 10^(−4) ≲ |Δm^2_(41)| ≲0.3 eV^2 mass range. The resulting limits on sin^2 2θ_(14) are improved by approx imately a factor of 2 over previous results and constitute the most stringent constraints to date in the |Δm^2_(41)| ≲ 0.2 eV^2 region.

Limits on active to sterile neutrino oscillations from disappearance searches in the MINOS, Daya Bay, and Bugey-3 experiments

Abstract: Searches for a light sterile neutrino have been performed independently by the MINOS and the Daya Bay experiments using the muon (anti)neutrino and electron antineutrino disappearance channels, respectively. In this Letter, results from both experiments are combined with those from the Bugey-3 reactor neutrino experiment to constrain oscillations into light sterile neutrinos. The three experiments are sensitive to complementary regions of parameter space, enabling the combined analysis to probe regions allowed by the Liquid Scintillator Neutrino Detector (LSND) and MiniBooNE experiments in a minimally extended four-neutrino flavor framework. Stringent limits on sin 2 2θ_(μe) are set over 6 orders of magnitude in the sterile mass-squared splitting Δm^2_(41). The sterile-neutrino mixing phase space allowed by the LSND and MiniBooNE experiments is excluded for Δm^2_(41) <0.8 eV^2 at 95% CL_s.

The Detector System of The Daya Bay Reactor Neutrino Experiment

Abstract: The Daya Bay experiment was the first to report simultaneous measurements of reactor antineutrinos at multiple baselines leading to the discovery of ν¯e oscillations over km-baselines. Subsequent data has provided the world׳s most precise measurement of sin^2 2θ_(13) and the effective mass splitting Δm^2_(ee). The experiment is located in Daya Bay, China where the cluster of six nuclear reactors is among the world׳s most prolific sources of electron antineutrinos. Multiple antineutrino detectors are deployed in three underground water pools at different distances from the reactor cores to search for deviations in the antineutrino rate and energy spectrum due to neutrino mixing. Instrumented with photomultiplier tubes, the water pools serve as shielding against natural radioactivity from the surrounding rock and provide efficient muon tagging. Arrays of resistive plate chambers over the top of each pool provide additional muon detection. The antineutrino detectors were specifically designed for measurements of the antineutrino flux with minimal systematic uncertainty. Relative detector efficiencies between the near and far detectors are known to better than 0.2%. With the unblinding of the final two detectors’ baselines and target masses, a complete description and comparison of the eight antineutrino detectors can now be presented. This paper describes the Daya Bay detector systems, consisting of eight antineutrino detectors in three instrumented water pools in three underground halls, and their operation through the first year of eight detector data-taking.

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 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.

Background Radiation Measurements at High Power Research Reactors

Abstract: Research reactors host a wide range of activities that make use of the intense neutron fluxes generated at these facilities. Recent interest in performing measurements with relatively low event rates, e.g. reactor antineutrino detection, at these facilities necessitates a detailed understanding of background radiation fields. Both reactor-correlated and naturally occurring background sources are potentially important, even at levels well below those of importance for typical activities. Here we describe a comprehensive series of background assessments at three high-power research reactors, including γ-ray, neutron, and muon measurements. For each facility we describe the characteristics and identify the sources of the background fields encountered. The general understanding gained of background production mechanisms and their relationship to facility features will prove valuable for the planning of any sensitive measurement conducted therein.

The Electronics and Data Acquisition System for the DarkSide-50 Veto Detectors

Abstract: DarkSide-50 is a detector for dark matter candidates in the form of weakly interacting massive particles It utilizes a liquid argon time projection chamber for the inner main detector, surrounded by a liquid scintillator veto (LSV) and a water Cherenkov veto detector (WCV) The LSV and WCV act as the neutron and cosmogenic muon veto detectors for DarkSide-50 This paper describes the electronics and data acquisition system used for these two detectors The system is made of a custom built front end electronics and commercial National Instruments high speed digitizers The front end electronics, the DAQ, and the trigger system have been used to acquire data in the form of zero-suppressed waveform samples from the 110 PMTs of the LSV and the 80 PMTs of the WCV The veto DAQ system has proven its performance and reliability This electronics and DAQ system can be scaled and used as it is for the veto of the next generation DarkSide-20k detector

CALIS - a CALibration Insertion System for the DarkSide-50 dark matter search experiment

Abstract: This paper describes the design, fabrication, commissioning and use of a CALibration source Insertion System (CALIS) in the DarkSide-50 direct dark matter search experiment. CALIS deploys radioactive sources into the liquid scintillator veto to characterize the detector response and detection efficiency of the DarkSide-50 Liquid Argon Time Projection Chamber, and the surrounding 30 t organic liquid scintillator neutron veto. It was commissioned in September 2014 and has been used successfully in several gamma and neutron source campaigns since then. A description of the hardware and an excerpt of calibration analysis results are given below.

Scenario Optimisation of Pumping Schedules in a Complex Water Supply System Considering a Cost–Risk Balancing Approach

Abstract: The optimisation of water pumping plant activation schedules is a significant issue when managing emergency and costly water transfer under a drought risk. This problem needs specific optimisation tools to deal with complex multi-reservoir supply systems and to consider different alternative scenarios. The effectiveness of emergency transfers alleviating droughts requires early warning and activation; on the other hand, the high operating costs of pump stations require system managers to take a robust approach that defines activation rules. The proposed optimisation procedure combines scenario optimisation analysis with a cost-risk balancing approach. The model searches for the identification of optimal decision rules by balancing the risk of water shortages and the operating costs of pumping stations. Scenario optimisation provides ‘barycentric’ values that define the activation threshold by comparing hydrological synthetic series results. A multi-objective approach is also required in order to balance energy cost minimisation requirements and a reduction of damage needs that can be caused by water shortages. Consequently, a scenario optimisation has been developed considering the multi-objective and cost-risk balancing problem. A model application has been developed optimising water management and energy costs in a real water system with shortage risks in the South Sardinia (Italy) region.

Effect of Low Electric Fields on Alpha Scintillation Light Yield in Liquid Argon

Abstract: Measurements were made of scintillation light yield of alpha particles from the $^{222}$Rn decay chain within the DarkSide-50 liquid argon time projection chamber. The light yield was found to increase as the applied electric field increased, with alphas in a 200 V/cm electric field exhibiting a 2% increase in light yield compared to alphas in no field.

The DarkSide project

Abstract: DarkSide is a graded experimental project based on radiopure argon, and is now, and will be, used in direct dark matter searches. The present DarkSide-50 detector, operating at the Gran Sasso National Laboratory, is a dual-phase, 50 kg, liquid argon time-projection-chamber surrounded by an active liquid scintillator veto. It is designed to be background free in 3 years of operation. DS-50 performances, when filled with atmospheric argon, are reported. However DS-50 filled with underground argon, shows impressive reduction of the (39)Ar isotope. The application of this powerful technology in a future generation of the DarkSide program is discussed.

DarkSide-50: status of the detector and results

Abstract: Yann Guardincerri∗1, P. Agnes2, I. F. M. Albuquerque41, T. Alexander48,1,30, A. K. Alton5, D. M. Asner30, H. O. Back30, B. Baldin1, K. Biery1, V. Bocci35, G. Bonfini4, W. Bonivento8, M. Bossa3,4, B. Bottino14,13, A. Brigatti25, J. Brodsky34, F. Budano39,40, S. Bussino39,40, M. Cadeddu9,8, L. Cadonati48, M. Cadoni9,8, F. Calaprice34, N. Canci16,4, A. Candela4, M. Caravati9,8, M. Cariello13, M. Carlini4, S. Catalanotti29,28, P. Cavalcante4, A. Chepurnov27, C. Cicalò8, A. G. Cocco28, G. Covone29,28, D. D’Angelo26,25, M. D’Incecco4, S. Davini3,4,13, S. De Cecco22, M. De Deo4, M. De Vincenzi39,40, A. Derbin31, A. Devoto9,8, F. Di Eusanio34, G. Di Pietro4,25, C. Dionisi35,37, E. Edkins15, A. Empl16, A. Fan47, G. Fiorillo29,28, K. Fomenko12, G. Forster48,1, D. Franco2, F. Gabriele4, C. Galbiati34,25, S. Giagu35,37, C. Giganti22, G. K. Giovanetti34, A. M. Goretti4, F. Granato44, L. Grandi10, M. Gromov27, M. Guan17, B. R. Hackett15, K. Herner1, D. Hughes34, P. Humble30, E. V. Hungerford16, Al. Ianni23,4, An. Ianni34,4, I. James39,40, T. N. Johnson45, C. Jollet43, K. Keeter11, C. L. Kendziora1, G. Koh34, D. Korablev12, G. Korga16,4, A. Kubankin6, X. Li34, M. Lissia8, B. Loer30, P. Lombardi25, G. Longo29,28, Y. Ma17, I. N. Machulin20,24, A. Mandarano3,4, S. M. Mari39,40, J. Maricic15, L. Marini14,13, C. J. Martoff44, A. Meregaglia43, P. D. Meyers34, R. Milincic15, J. D. Miller16, D. Montanari1, A. Monte48, B. J. Mount11, V. N. Muratova31, P. Musico13, J. Napolitano44, A. Navrer Agasson22, S. Odrowski4, M. Orsini4, F. Ortica33,32, L. Pagani14,13, M. Pallavicini14,13, E. Pantic45, S. Parmeggiano25, K. Pelczar19, N. Pelliccia33,32, A. Pocar48,34, S. Pordes1, D. A. Pugachev20,24, H. Qian34, K. Randle34, G. Ranucci25, M. Razeti8, A. Razeto4,34, B. Reinhold15, A. L. Renshaw16,47, M. Rescigno35, Q. Riffard2, A. Romani33,32, B. Rossi28,34, N. Rossi4, D. Rountree49, D. Sablone4, P. Saggese25, R. Saldanha10, W. Sands34, C. Savarese3,4, B. Schlitzer45, E. Segreto7, D. A. Semenov31, E. Shields34, P. N. Singh16, M. D. Skorokhvatov20,24, O. Smirnov12, A. Sotnikov12, C. Stanford34, Y. Suvorov47,4,20, R. Tartaglia4, J. Tatarowicz44, G. Testera13, A. Tonazzo2, P. Trinchese29,28, E. V. Unzhakov31, M. Verducci35,37, A. Vishneva12, B. Vogelaar49, M. Wada34, S. Walker29,28, H. Wang47, Y. Wang17,47, A. W. Watson44, S. Westerdale34, J. Wilhelmi44, M. M. Wojcik19, Xi. Xiang34, X. Xiao47, J. Xu34, C. Yang17, A. Zec48, W. Zhong17, C. Zhu34, G. Zuzel19

The Electronics and Data Acquisition System for the DarkSide-50 Veto Detectors

Abstract: DarkSide-50 is a detector for dark matter candidates in the form of weakly interacting massive particles (WIMPs). It utilizes a liquid argon time projection chamber (LAr TPC) for the inner main detector. The TPC is surrounded by a liquid scintillator veto (LSV) and a water Cherenkov veto detector (WCV). The LSV and WCV, both instrumented with PMTs, act as the neutron and cosmogenic muon veto detectors for DarkSide-50. This paper describes the electronics and data acquisition system used for these two detectors.