52 research outputs found

    Measuring cosmogenic Li9 background in a reactor neutrino experiment

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    Cosmogenic isotopes 9Li and 8He produced in the detector are the most problematic background in the reactor neutrino experiments designed to determine precisely the neutrino mixing angle theta13. The average time interval of cosmic-ray muons in the detector is often on the order of the lifetimes of the 9Li and 8He isotopes. We have developed a method for determining this kind of background from the distribution of time since last muon for muon rate up to about 20 Hz when the background-to-signal ratio is small, on the order of a few percents.Comment: 9 pages, 3 figures. To appear in NIM

    Scale-dependent galaxy bias, CMB lensing-galaxy cross-correlation, and neutrino masses

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    One of the most powerful cosmological datasets when it comes to constraining neutrino masses is represented by galaxy power spectrum measurements, Pgg(k)P_{gg}(k). The constraining power of Pgg(k)P_{gg}(k) is however severely limited by uncertainties in the modeling of the scale-dependent galaxy bias b(k)b(k). In this Letter we present a new method to constrain b(k)b(k) by using the cross-correlation between the Cosmic Microwave Background (CMB) lensing signal and galaxy maps (CκgC_\ell^{\rm \kappa g}) using a simple but theoretically well-motivated parametrization for b(k)b(k). We apply the method using CκgC_\ell^{\rm \kappa g} measured by cross-correlating Planck lensing maps and the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 11 (DR11) CMASS galaxy sample, and Pgg(k)P_{gg}(k) measured from the BOSS DR12 CMASS sample. We detect a non-zero scale-dependence at moderate significance, which suggests that a proper modeling of b(k)b(k) is necessary in order to reduce the impact of non-linearities and minimize the corresponding systematics. The accomplished increase in constraining power of Pgg(k)P_{gg}(k) is demonstrated by determining a 95% C.L. upper bound on the sum of the three active neutrino masses MνM_{\nu} of Mν<0.19eVM_{\nu}<0.19\, {\rm eV}. This limit represents a significant improvement over previous bounds with comparable datasets. Our method will prove especially powerful and important as future large-scale structure surveys will overlap more significantly with the CMB lensing kernel providing a large cross-correlation signal.Comment: 11 pages, 3 figure

    An overview of the Daya Bay Reactor Neutrino Experiment

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    The Daya Bay Reactor Neutrino Experiment discovered an unexpectedly large neutrino oscillation related to the mixing angle θ13\theta_{13} in 2012. This finding paved the way to the next generation of neutrino oscillation experiments. In this article, we review the history, featured design, and scientific results of Daya Bay. Prospects of the experiment are also described.Comment: 18 pages, 5 figures. An overview to appear in the Special Issue on neutrino oscillations of Nuclear Physics

    Waterproofed Photomultiplier Tube Assemblies for the Daya Bay Reactor Neutrino Experiment

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    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.Comment: 16 pages, 11 figures. Submitted to Nucl. Instr. Met