U.S. Department of Energy

Pacific Northwest National Laboratory

FY2016 Publications

PUBLICATIONS

2016

Dark matter search results from the PICO-60 CF3 i bubble chamber : Amole, C., Ardid, M., Asner, D. M., Baxter, D., Behnke, E., Bhattacharjee, P., ... (PICO Collaboration) (2016). Dark matter search results from the PICO-60 CF3 i bubble chamber. Physical Review D - Particles, Fields, Gravitation and Cosmology, 93(5), [052014]. DOI: 10.1103/PhysRevD.93.052014

New data are reported from the operation of the PICO-60 dark matter detector, a bubble chamber filled with 36.8 kg of CF3I and located in the SNOLAB underground laboratory. PICO-60 is the largest bubble chamber to search for dark matter to date. With an analyzed exposure of 92.8 livedays, PICO-60 exhibits the same excellent background rejection observed in smaller bubble chambers. Alpha decays in PICO-60 exhibit frequency-dependent acoustic calorimetry, similar but not identical to that reported recently in a C3F8 bubble chamber. PICO-60 also observes a large population of unknown background events, exhibiting acoustic, spatial, and timing behaviors inconsistent with those expected from a dark matter signal. These behaviors allow for analysis cuts to remove all background events while retaining 48.2% of the exposure. Stringent limits on weakly interacting massive particles interacting via spin-dependent proton and spin-independent processes are set, and most interpretations of the DAMA/LIBRA modulation signal as dark matter interacting with iodine nuclei are ruled out.

Improved dark matter search results from PICO-2L Run 2 : Amole, C., Ardid, M., Arnquist, I. J., Asner, D. M., Baxter, D., Behnke, E., ... (PICO Collaboration) (2016). Improved dark matter search results from PICO-2L Run 2. Physical Review D - Particles, Fields, Gravitation and Cosmology, 93(6), [061101]. DOI: 10.1103/PhysRevD.93.061101

New data are reported from a second run of the 2-liter PICO-2L C3F8 bubble chamber with a total exposure of 129 kg-days at a thermodynamic threshold energy of 3.3 keV. These data show that measures taken to control particulate contamination in the superheated fluid resulted in the absence of the anomalous background events observed in the first run of this bubble chamber. One single nuclear-recoil event was observed in the data, consistent both with the predicted background rate from neutrons and with the observed rate of unambiguous multiple-bubble neutron scattering events. The chamber exhibits the same excellent electron-recoil and alpha decay rejection as was previously reported. These data provide the most stringent direct detection constraints on weakly interacting massive particle (WIMP)-proton spin-dependent scattering to date for WIMP masses <50 GeV/c2.

Measurement of the Higgs boson mass and eþe− → ZH cross section using Z → μþμ− and Z → eþe− at the ILC : J., Yan, S., Watanuki, K., Fuji, A., Ishikawa, D., Jeans, J., Strube, J., Tian, H., Yamamoto.  Measurement of the Higgs boson mass and eþe− → ZH cross section using Z → μþμ− and Z → eþe− at the ILC.  Physical Review D - Particles, Fields, Gravitation, and Cosomolgy, 94, 113002 (2016) DOI: 10.1103/PhysRevD.94.113002

This paper presents a full simulation study of the measurement of the production cross section (σZH ) of the Higgsstrahlung process e+e−→ZH and the Higgs boson mass (MH ) at the International Linear Collider (ILC), using events in which a Higgs boson recoils against a Z boson decaying into a pair of muons or electrons. The analysis is carried out for three center-of-mass energies √s=250 , 350, and 500 GeV, and two beam polarizations e−Le+R and e−Re+L , for which the polarizations of e− and e+ are (Pe−,Pe+)=(−80%,+30%) and (+80% , −30% ), respectively. Assuming an integrated luminosity of 250  fb−1 for each beam polarization at √s=250  GeV , where the best lepton momentum resolution is obtainable, σZH and MH can be determined with a precision of 2.5% and 37 MeV for e−Le+R and 2.9% and 41 MeV for e−Re+L , respectively. Regarding a 20 year ILC physics program, the expected precisions for the HZZ coupling and MH are estimated to be 0.4% and 14 MeV, respectively. The event selection is designed to optimize the precisions of σZH and MH while minimizing the bias on the measured σZH due to discrepancy in signal efficiencies among Higgs decay modes. For the first time, model independence has been demonstrated to a sub-percent level for the σZH measurement at each of the three center-of-mass energies. The results presented show the impact of center-of-mass energy and beam polarization on the evaluated precisions and serve as a benchmark for the planning of the ILC run scenario.

The Darkside Awakens : Davini, S., Agnes, P., Agostino, L., Albuquerque, I. F., Alexander, T., Alton, A. K., . . . Zuzel, G. (2016). The DarkSide awakens. Journal of Physics: Conference Series, 718, 042016. DOI: 10.1088/1742-6596/718/4/042016

 

The DarkSide program at LNGS aims to perform background-free WIMP searches using two phase liquid argon time projection chambers, with the ultimate goal of covering all parameters down to the so-called neutrino oor. One of the distinct features of the program is the use of underground argon with has a reduced content of the radioactive 39Ar compared to atmospheric argon. The DarkSide Collaboration is currently operating the DarkSide-50 experiment, the first such WIMP detector using underground argon. Operations with underground argon indicate a suppression of 39Ar by a factor (1:4 0:2) 103 relative to atmospheric argon. The new results obtained with DarkSide-50 and the plans for the next steps of the DarkSide program, the 20 t fiducial mass DarkSide-20k detector and the 20t fiducial Argo, are reviewed in this proceedings.

 

2017

Convolutional neural networks applied to neutrino events in a liquid argon time projection chamber : Acciarri, R., Adams, C., An, R., Asaadi, J., Auger, M., Bagby, L., ... Zhang, C. (2017). Convolutional neural networks applied to neutrino events in a liquid argon time projection chamber. Journal of Instrumentation, 12(3), [P03011]. DOI: 10.1088/1748-0221/12/03/P03011

We present several studies of convolutional neural networks applied to data coming from the MicroBooNE detector, a liquid argon time projection chamber (LArTPC). The algorithms studied include the classification of single particle images, the localization of single particle and neutrino interactions in an image, and the detection of a simulated neutrino event overlaid with cosmic ray backgrounds taken from real detector data. These studies demonstrate the potential of convolutional neural networks for particle identification or event detection on simulated neutrino interactions. We also address technical issues that arise when applying this technique to data from a large LArTPC at or near ground level.

Determining the neutrino mass with Cyclotron Radiation Emission Spectroscopy – Project 8 : Project 8 Collaboration (Ashtari Esfahani, Ali et al.), Determining the neutrino mass with Cyclotron Radiation Emission Spectroscopy – Project 8 J.Phys. G44 (2017) no.5, 054004, DOI: 10.1088/1361-6471/aa5b4f

The most sensitive direct method to establish the absolute neutrino mass is observation of the endpoint of the tritium beta-decay spectrum. Cyclotron Radiation Emission Spectroscopy (CRES) is a precision spectrographic technique that can probe much of the unexplored neutrino mass range with O(eV) resolution. A lower bound of m(e) & 9(0:1)meV is set by observations of neutrino oscillations, while the KATRIN Experiment { the current-generation tritium beta-decay experiment that is based on Magnetic Adiabatic Collimation with an Electrostatic (MAC-E) filter sensitivity of m(e) . 0:2 eV. The CRES technique aims to avoid the diculties in scaling up a MAC-E filter-based experiment to achieve a lower mass sensitivity. In this paper we review the current status of the CRES technique and describe Project 8, a phased absolute neutrino mass experiment that has the potential to reach sensitivities down to m(e) . 40meV using an atomic tritium source.

Mass Spectrometric Determination of Uranium and Thorium in High Radiopurity Polymers using Ultra Low Background Electroformed Copper Crucibles for Dry Ashing : Arnquist, I. J., Hoppe, E. J., Bliss, M., & Grate, J. W. (2017). Mass Spectrometric Determination of Uranium and Thorium in High Radiopurity Polymers Using Ultra Low Background Electroformed Copper Crucibles for Dry Ashing. Analytical Chemistry, 89(5), 3101-3107. DOI:10.1021/acs.analchem.6b04854

A rapid new method for determining the U and Th mass concentrations in high radiopurity plastics is described, consisting of (1) dry ashing the plastic sample and tracers in low mass crucibles made of ultra low background electroformed copper (ULB EF-Cu) foil cut and folded into boats, (2) dissolving both the ash and the boat in acid, (3) performing a column separation to remove copper, and (4) determining the elements of interest by isotope dilution mass spectrometry. This method was demonstrated on both unfluorinated and fluorinated plastics, demonstrating high tracer recoveries and detection limits to pg/g (i.e., parts per trillion) levels or below, corresponding to μBq/kg of material. Samples of biomedical polyester (Max-Prene 955) and a fluoropolymer (polyvinylidene fluoride, PVDF) were analyzed in powder raw material forms as well as solids in the form of pellets or injection molded parts.

The quick and ultrasensitive determination of K in NaI using inductively coupled plasma mass spectrometry : Arnquist, I. J., & Hoppe, E. W. (2017). The quick and ultrasensitive determination of K in NaI using inductively coupled plasma mass spectrometry. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 851, 15-19.  DOI: https://doi.org/10.1016/j.nima.2017.01.064

A highly sensitive, novel and quick assay method utilizing inductively coupled plasma mass spectrometry was developed for the determination of K in NaI powders and NaI(Tl) scintillator crystals for use in ultralow background applications.

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