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Register a new userThe calibration of the Sudbury Neutrino Observatory using uniformly distributed radioactive sources
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The production and analysis of distributed sources of 24Na and 222Rn in the Sudbury Neutrino Observatory (SNO) are described. These unique sources provided accurate calibrations of the response to neutrons, produced through photodisintegration of the deuterons in the heavy water target, and to low energy betas and gammas. The application of these sources in determining the neutron detection efficiency and response of the 3He proportional counter array, and the characteristics of background Cherenkov light from trace amounts of natural radioactivity is described.
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A calibration source using gamma-rays from 16N (t_1/2 = 7.13 s) beta-decay has been developed for the Sudbury Neutrino Observatory (SNO) for the purpose of energy and other calibrations. The 16N is produced via the (n,p) reaction on 16O in the form of CO2 gas using 14-MeV neutrons from a commercially available Deuterium-Tritium (DT) generator. The 16N is produced in a shielding pit in a utility room near the SNO cavity and transferred to the water volumes (D2O or H2O) in a CO2 gas stream via small diameter capillary tubing. The bulk of the activity decays in a decay/trigger chamber designed to block the energetic beta-particles yet permit the primary branch 6.13 MeV gamma-rays to exit. Detection of the coincident beta-particles with plastic scintillator lining the walls of the decay chamber volume provides a tag for the SNO electronics. This paper gives details of the production, transfer, and triggering systems for this source along with a discussion of the source gamma-ray output and performance.
The long baseline between the Earth and the Sun makes solar neutrinos an excellent test beam for exploring possible neutrino decay. The signature of such decay would be an energy-dependent distortion of the traditional survival probability which can be fit for using well-developed and high precision analysis methods. Here a model including neutrino decay is fit to all three phases of $^8$B solar neutrino data taken by the Sudbury Neutrino Observatory. This fit constrains the lifetime of neutrino mass state $ u_2$ to be ${>8.08times10^{-5}}$ s/eV at $90%$ confidence. An analysis combining this SNO result with those from other solar neutrino experiments results in a combined limit for the lifetime of mass state $ u_2$ of ${>1.04times10^{-3}}$ s/eV at $99%$ confidence.
We report results from a combined analysis of solar neutrino data from all phases of the Sudbury Neutrino Observatory. By exploiting particle identification information obtained from the proportional counters installed during the third phase, this analysis improved background rejection in that phase of the experiment. The combined analysis resulted in a total flux of active neutrino flavors from 8B decays in the Sun of (5.25 pm 0.16(stat.)+0.11-0.13(syst.))times10^6 cm^{-2}s^{-1}. A two-flavor neutrino oscillation analysis yielded Deltam^2_{21} = (5.6^{+1.9}_{-1.4})times10^{-5} eV^2 and tan^2{theta}_{12}= 0.427^{+0.033}_{-0.029}. A three-flavor neutrino oscillation analysis combining this result with results of all other solar neutrino experiments and the KamLAND experiment yielded Deltam^2_{21} = (7.41^{+0.21}_{-0.19})times10^{-5} eV^2, tan^2{theta}_{12} = 0.446^{+0.030}_{-0.029}, and sin^2{theta}_{13} = (2.5^{+1.8}_{-1.5})times10^{-2}. This implied an upper bound of sin^2{theta}_{13} < 0.053 at the 95% confidence level (C.L.).
Neutrons produced in nuclear interactions initiated by cosmic-ray muons present an irreducible background to many rare-event searches, even in detectors located deep underground. Models for the production of these neutrons have been tested against previous experimental data, but the extrapolation to deeper sites is not well understood. Here we report results from an analysis of cosmogenically produced neutrons at the Sudbury Neutrino Observatory. A specific set of observables are presented, which can be used to benchmark the validity of GEANT4 physics models. In addition, the cosmogenic neutron yield, in units of $10^{-4};text{cm}^{2}/left(text{g}cdotmuright)$, is measured to be $7.28 pm 0.09;text{stat.} ^{+1.59}_{-1.12};text{syst.}$ in pure heavy water and $7.30 pm 0.07;text{stat.} ^{+1.40}_{-1.02};text{syst.}$ in NaCl-loaded heavy water. These results provide unique insights into this potential background source for experiments at SNOLAB.
Experimental tests of Lorentz symmetry in systems of all types are critical for ensuring that the basic assumptions of physics are well-founded. Data from all phases of the Sudbury Neutrino Observatory, a kiloton-scale heavy water Cherenkov detector, are analyzed for possible violations of Lorentz symmetry in the neutrino sector. Such violations would appear as one of eight possible signal types in the detector: six seasonal variations in the solar electron neutrino survival probability differing in energy and time dependence, and two shape changes to the oscillated solar neutrino energy spectrum. No evidence for such signals is observed, and limits on the size of such effects are established in the framework of the Standard Model Extension, including 40 limits on perviously unconstrained operators and improved limits on 15 additional operators. This makes limits on all minimal, Dirac-type Lorentz violating operators in the neutrino sector available for the first time.
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