Sudbury Neutrino Observatory Detector Research Articles

Current Status and Future Prospects of the SNO+ Experiment

SNO+ is a large liquid scintillator-based experiment located 2 km underground at SNOLAB, Sudbury, Canada. It reuses the Sudbury Neutrino Observatory detector, consisting of a 12 m diameter acrylic vessel which will be filled with about 780 tonnes of ultra-pure liquid scintillator. Designed as a multipurpose neutrino experiment, the primary goal of SNO+ is a search for the neutrinoless double-beta decay (0νββ) of130Te. In Phase I, the detector will be loaded with 0.3% natural tellurium, corresponding to nearly 800 kg of130Te, with an expected effective Majorana neutrino mass sensitivity in the region of 55–133 meV, just above the inverted mass hierarchy. Recently, the possibility of deploying up to ten times more natural tellurium has been investigated, which would enable SNO+ to achieve sensitivity deep into the parameter space for the inverted neutrino mass hierarchy in the future. Additionally, SNO+ aims to measure reactor antineutrino oscillations, low energy solar neutrinos, and geoneutrinos, to be sensitive to supernova neutrinos, and to search for exotic physics. A first phase with the detector filled with water will begin soon, with the scintillator phase expected to start after a few months of water data taking. The0νββPhase I is foreseen for 2017.

SNO and the new SNOLAB

A new international science laboratory, SNOLAB, has recently begun operation 2 km underground at the site of the Sudbury Neutrino Observatory (SNO), near Sudbury, Canada. The laboratory incorporates the SNO detector and includes several new experimental areas with a total excavated volume about three times larger than the original SNO cavity. The SNO detector has now completed operation with heavy water and data analysis is being completed with improved accuracy by combining all three phases of the project. A new project, SNO +, has recently been funded and will provide high sensitivity for neutrino-less double beta decay, low energy solar neutrinos, geoneutrinos, supernovae and other physics measurements. A number of dark matter measurements are in progress or preparing for deployment and a new supernova measurement, HALO is also being deployed. The status and physics objectives of the experimental program is outlined.

Monte Carlo for the NCD phase of the Sudbury Neutrino Observatory

In the third phase of the Sudbury Neutrino Observatory (SNO) experiment an array of 3He proportional counters was added deployed in the heavy-water volume of the SNO detector. This Neutral-Current Detection (NCD) Array detected the neutrons from the neutral-current interaction of 8B solar neutrinos with deuterium. Before we can determine the neutrino flux we must separate the neutron-capture pulses from pulses due to alpha particles and instrumental backgrounds. We have created a unique, detailed simulation of the current pulses from the proportional counters that includes energy straggling, ion drift, electron diffusion, space charge, and electronics effects. We have conducted extensive studies to determine the accuracy of the simulation. In the solar neutrino analysis the NCD Monte Carlo is used to determine the energy spectrum of the alpha background, as well as the applicable systematic effects. In the near future it will be used to fit the data pulses to separate neutron-capture and alpha pulses. With this pulse-shape analysis method the differences between pulse characteristics can be associated directly with the physical mechanisms of track formation and charge motion in the counter gas.

News from the Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory (SNO) has now completed neutrino detection with 1,000 tonnes of heavy water situated 2,000 meters underground in INCO's Creighton Mine near Sudbury, Ontario. During the first two phases of the experiment, SNO showed that neutrinos change flavour on their way to earth and accurately measured the solar neutrino oscillation parameters. Besides this, SNO was also able to use the data of these first two phases for other analyses. In particular, it recently set a limit on the Solar hep Reaction and the diffuse Supernova background. The third and final phase of operation uses an array of neutron detectors to independently observe the Neutral Current reaction of solar neutrinos on deuterium. Data analysis of this phase is in progress. In this paper, I discuss the latest results of the first two phases of the SNO experiment and report on the operation and calibration of the SNO detector during the it's final phase.

Wavelength shifters for water Cherenkov detectors

The light yield of a water-based Cherenkov detector can be significantly improved by adding a wavelength shifter (WLS). WLS molecules absorb ultraviolet photons and re-emit them at longer wavelengths where typical photomultiplier tubes are more sensitive. In this study, several WLS compounds are tested for possible deployment in the Sudbury Neutrino Observatory (SNO). Test results on optical properties and chemical compatibility for a few WLS candidates are reported; together with timing and gain measurements. A Monte Carlo simulation of the SNO detector response is used to estimate the total light gain with WLS. Finally, a cosmic ray Cherenkov detector was built to investigate the optical properties of WLS.

An array of low-background 3He proportional counters for the Sudbury Neutrino Observatory

An array of Neutral-Current Detectors (NCDs) has been built in order to make a unique measurement of the total active flux of solar neutrinos in the Sudbury Neutrino Observatory (SNO). Data in the third phase of the SNO experiment were collected between November 2004 and 2006, after the NCD array was added to improve the neutral-current sensitivity of the SNO detector. This array consisted of 36 strings of proportional counters filled with a mixture of 3He and CF 4 gas capable of detecting the neutrons liberated by the neutrino-deuteron neutral-current reaction in the D 2O, and four strings filled with a mixture of 4He and CF 4 gas for background measurements. The proportional counter diameter is 5 cm. The total deployed array length was 398 m. The SNO NCD array is the lowest-radioactivity large array of proportional counters ever produced. This article describes the design, construction, deployment, and characterization of the NCD array, discusses the electronics and data acquisition system, and considers event signatures and backgrounds.

Determination of theνeand totalB8solar neutrino fluxes using the Sudbury Neutrino Observatory Phase I data set

This article provides the complete description of results from the Phase I data set of the Sudbury Neutrino Observatory (SNO). The Phase I data set is based on a 0.65 kt-year exposure of heavy water to the solar $^8$B neutrino flux. Included here are details of the SNO physics and detector model, evaluations of systematic uncertainties, and estimates of backgrounds. Also discussed are SNO's approach to statistical extraction of the signals from the three neutrino reactions (charged current, neutral current, and elastic scattering) and the results of a search for a day-night asymmetry in the $\nu_e$ flux. Under the assumption that the $^8$B spectrum is undistorted, the measurements from this phase yield a solar $\nu_e$ flux of $\phi(\nu_e) = 1.76^{+0.05}_{-0.05}{(stat.)}^{+0.09}_{-0.09} {(syst.)} \times 10^{6}$ cm$^{-2}$ s$^{-1}$, and a non-$\nu_e$ component $\phi(\nu_{\mu\tau}) = 3.41^{+0.45}_{-0.45}{(stat.)}^{+0.48}_{-0.45} {(syst.)} \times 10^{6}$ cm$^{-2}$ s$^{-1}$. The sum of these components provides a total flux in excellent agreement with the predictions of Standard Solar Models. The day-night asymmetry in the $\nu_e$ flux is found to be $A_{e} = 7.0 \pm 4.9 \mathrm{(stat.)^{+1.3}_{-1.2}}% \mathrm{(sys.)}$, when the asymmetry in the total flux is constrained to be zero.

Recent results from the sudbury neutrino observatory

The Sudbury Neutrino Observatory (SNO) measures both the flux of the electron-type neutrinos and the total flux of all active flavours of neutrinos originating from the Sun. A model-independent test of neutrino flavour transformation was performed by comparing these two measurements. In 2002, this flavour transformation was definitively demonstrated. In this talk, results from these measurements and the current status of the SNO detector are presented.

Measurement of [formula omitted] dissolved in water at the Sudbury Neutrino Observatory

The technique used at the Sudbury Neutrino Observatory (SNO) to measure the concentration of 222 Rn in water is described. Water from the SNO detector is passed through a vacuum degasser (in the light water system) or a membrane contact degasser (in the heavy water system) where dissolved gases, including radon, are liberated. The degasser is connected to a vacuum system which collects the radon on a cold trap and removes most other gases, such as water vapor and N 2. After roughly 0.5 tonnes of H 2O or 6 tonnes of D 2O have been sampled, the accumulated radon is transferred to a Lucas cell. The cell is mounted on a photomultiplier tube which detects the α-particles from the decay of 222 Rn and its progeny. The overall degassing and concentration efficiency is about 38% and the single-α counting efficiency is approximately 75%. The sensitivity of the radon assay system for D 2O is equivalent to ∼3×10 −15 g U/g water. The radon concentration in both the H 2O and D 2O is sufficiently low that the rate of background events from U-chain elements is a small fraction of the interaction rate of solar neutrinos by the neutral current reaction.

André Stephane Hamer

André Stephane Hamer, an accomplished young experimental physicist who was a major contributor to the success of the Sudbury Neutrino Observatory (SNO), died on 2 February 2003 in Ottawa, Ontario, Canada, after a courageous battle with colon cancer. André was born on 17 January 1968 in Oshawa, Ontario. He was raised in a stimulating environment by loving parents who fostered his natural curiosity and provided him with broad learning opportunities. On completing high school, he obtained a BSc in physics at the University of Toronto in 1993 and moved on to graduate work at Queen’s University in Kingston, Ontario. He quickly demonstrated his strong aptitude and love for experimental physics. For his master’s degree work, André contributed to the ultrasensitive measurements of radioactivity used in SNO by developing a new technique for efficient assay of a few atoms of radon. He earned his MSc in 1997.Continuing his doctoral work, also with one of us (McDonald), he made substantial contributions to the success of SNO by developing calibration devices and by providing a detailed understanding of the physics performance of the detector itself. André developed the primary energy calibration standard for the SNO detector: a source of radioactive nitrogen (16N) and lithium (8Li) that is produced by a neutron generator and transported to the center of the SNO detector via capillary tubing and that decays within a scintillator-lined chamber. The 16N source provided a triggered source of 6.13-MeV gamma rays with an accuracy of better than 1%. André designed and constructed this source, and used it and others to develop the full energy calibration for the SNO measurements.André graduated with his PhD in 1999 and continued to work on the SNO project as a postdoctoral fellow at Los Alamos National Laboratory with the group led by one of us (Hime). He contributed substantially to the analyses in the first SNO publications in 2001 and 2002. On behalf of the SNO collaboration, he presented the first results of the comparison of the neutral-current and charged-current interactions on deuterium at the American Physical Society conference in Albuquerque, New Mexico, in April 2002. The results provided compelling evidence for flavor change for solar neutrinos. All André’s work, whether experimental or analytical, was done to completion, well designed, implemented, documented, and intended to be used for the long term. He was also a leader, recognized by his colleagues as someone whose infectious enthusiasm and strong example should be followed. He approached projects completely, organized the work, and performed the most difficult tasks himself, because he really loved what he was doing. His sense of humor was evident at all times: A typical quip to a colleague while seeking a repair device at a local hardware store: “The two most important tools of the experimental physicist must be the car and the cell phone!”André’s colleagues are benefiting from his legacy as they continue with the further phases of the SNO experiment. Unfortunately, his strong scientific contributions were cut short by his death not long after he had accepted a new position with the underground science laboratory (SNOLab) that is being developed in Canada.André was a devoted husband and a loving father of three sons; the youngest was born one month after André died. He had already begun to impart his love for life, education, and science to his young sons. The SNO collaboration has established a fund in André’s memory for his children’s future education. André gave 100% in all things: as a scientist, colleague, friend, father, husband, and family man. The world has lost a wonderful scientist at far too young an age. André Stephane Hamer PPT|High resolution© 2003 American Institute of Physics.

The 8Li calibration source for the Sudbury Neutrino Observatory

A calibration source employing 8Li ( t 1/2=0.838 s) has been developed for use with the Sudbury Neutrino Observatory (SNO). This source creates a spectrum of β-particles with an energy range similar to that of the SNO 8B solar neutrino signal. The source is used to test the SNO detector's energy response, position reconstruction and data reduction algorithms. The 8Li isotope is created using a deuterium–tritium neutron generator in conjunction with a 11B target, and is carried to a decay chamber using a gas/aerosol transport system. The decay chamber detects prompt α-particles by gas scintillation in coincidence with the β-particles which exit through a thin stainless steel wall. A description is given of the production, transport, and tagging techniques along with a discussion of the performance and application of the source.

Catching some Zs: The solar neutrino problem, neutral current interactions, and the Sudbury Neutrino Observatory

The Solar Neutrino Problem (SNP) rivals CP violation as one of the oldest problems in physics that lacks a compelling explanation. The Sudbury Neutrino Observatory (SNO)—a heavy-water Cherenkov detector—is the first solar neutrino experiment that has the ability to discriminate signals from different neutrino flavors. Since all three presently known flavors participate in Zo exchange, SNO is extremely sensitive to neutrino oscillations. A brief overview of the SNP is given, including a discussion of sterile neutrinos. The ability of SNO to discriminate between the various possible solutions to the SNP is also discussed. The SNO detector is described, including a description of the neutral-current detection methods, and the current status of the experiment is given.

Solar neutrino event spectra: Tuning SNO to equalize Super-Kamiokande

The Super-Kamiokande (SK) and the Sudbury Neutrino Observatory (SNO) experiments are monitoring the flux of B solar neutrinos through the electron energy spectrum from the reactions nu_{e,mu,tau} + e --> nu_{e,mu,tau} + e and nu_e + d --> p + p + e, respectively. We show that the SK detector response to B neutrinos in each bin of the electron energy spectrum (above 8 MeV) can be approximated, with good accuracy, by the SNO detector response in an appropriate electron energy range (above 5.1 MeV). For instance, the SK response in the bin [10,10.5] MeV is reproduced (``equalized'') within 2 percent by the SNO response in the range [7.1,11.75] MeV. As a consequence, in the presence of active neutrino oscillations, the SK and SNO event rates in the corresponding energy ranges turn out to be linearly related, for any functional form of the oscillation probability. Such equalization is not spoiled by the possible contribution of hep neutrinos (within current phenomenological limits). In perspective, when the SK and the SNO spectra will both be measured with high accuracy, the SK-SNO equalization can be used to determine the absolute B neutrino flux, and to cross-check the (non)observation of spectral deviations in SK and SNO. At present, as an exercise, we use the equalization to ``predict'' the SNO energy spectrum, on the basis of the current SK data. Finally, we briefly discuss some modifications or limitations of our results in the case of sterile neutrino oscillations and of relatively large Earth matter effects.

Day-night effect predictions for the SNO detector

Detailed predictions for the day-night (D-N) asymmetry in the energy-integrated one year signals in the Sudbury Neutrino Observatory (SNO) detector in the case of the Mikheyev-Smirnov-Wolfenstein (MSW) ${\ensuremath{\nu}}_{e}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\mu}(\ensuremath{\tau})}$ and/or ${\ensuremath{\nu}}_{e}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{s}$ transition solutions of the solar neutrino problem are presented. The asymmetries in the charged current (CC) and $\ensuremath{\nu}\ensuremath{-}{e}^{\ensuremath{-}}$ elastic-scattering (ES) event rates are calculated for both MSW solutions; in the case of the ${\ensuremath{\nu}}_{e}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{s}$ transition solution the D-N asymmetry in the neutral current (NC) event rate are derived as well. The asymmetries are calculated for three night samples of events which are produced by the solar neutrinos crossing (i) the Earth's mantle only (Mantle), (ii) the Earth's core (Core) and (iii) the Earth's core and/or the mantle (Night). The effects of the uncertainties (i) in the values of the cross sections of the CC and NC neutrino-induced reactions on deuterium, and (ii) in the value of the bulk matter density and/or the chemical composition of the Earth's core, on the corresponding D-N asymmetry predictions are analyzed. It is shown, in particular, that due to the strong enhancement of the transitions of the solar neutrinos crossing the Earth's core, at ${\mathrm{sin}}^{2}2{\ensuremath{\theta}}_{V}<~0.01,$ the corresponding one year average D-N asymmetry in the Core sample of CC events in the case of the ${\ensuremath{\nu}}_{e}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\mu}(\ensuremath{\tau})}$ solution can be larger by a factor of up to $\ensuremath{\sim}8$ than the asymmetry in the Night sample. In certain subregions of the MSW solution regions at small ${\mathrm{sin}}^{2}2{\ensuremath{\theta}}_{V},$ the predicted magnitude of the Core D-N asymmetry in the CC sample is very sensitive to the value of the electron fraction number in the Earth's core. Iso-(D-N) asymmetry contours in the $\ensuremath{\Delta}{m}^{2}\ensuremath{-}{\mathrm{sin}}^{2}2{\ensuremath{\theta}}_{V}$ plane for the SNO detector are derived in the region ${\mathrm{sin}}^{2}2{\ensuremath{\theta}}_{V}\ensuremath{\gtrsim}{10}^{\ensuremath{-}4}$ for the Core and Night samples of the CC, ES, and NC events. The dependence of the D-N asymmetries considered on the final-state ${e}^{\ensuremath{-}}$ threshold energy in the CC and ES reactions is also investigated. Our results show, in particular, that the SNO experiment will be able to probe a substantial part of the small mixing angle and most of the large mixing angle MSW ${\ensuremath{\nu}}_{e}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\mu}(\ensuremath{\tau})}$ solution regions by performing Night and Core D-N asymmetry measurements.

Low-background /sup 3/He proportional counters for use in the Sudbury neutrino observatory

Current solar neutrino detectors measure a considerably lower flux of electron-flavor neutrinos than predicted by solar models. This could be an indication of neutrino oscillations, which would provide direct evidence that neutrinos have mass. The Sudbury Neutrino Observatory (SNO) was designed to detect all flavors of neutrinos, and will provide a rigorous test of this theory. The SNO detector's heavy water target gives it the unique ability to detect all non-sterile neutrino flavors via the neutral-current (NC) break-up of the deuteron. This NC interaction liberates a neutron which may be detected with an array of discrete /sup 3/He proportional counters. The strict radioactivity requirements imposed by the need for low backgrounds dictate the use of ultra-pure materials and processes in building these counters. Additionally, they must survive in the heavy water environment for several years. The design, construction, and testing of these unique counters are described.

The sudbury neutrino observatory project

The construction of the Sudbury Neutrino Observatory (SNO) project was completed in April, 1998 and the detector is presently in operation as it is being filled with light and heavy water. The SNO detector is a 1,000 tonne heavy water Cerenkov detector situated 2,000 meters underground in INCO's Creighton Mine near Sudbury, Ontario, Canada. [1] The project is a Canadian, US and UK collaboration. Through the use of heavy water SNO will be able to detect a number of neutrino reactions, including one sensitive specifically to electron neutrinos and another one which is sensitive to all neutrino types. With these two reactions the detector will be used to search for solar neutrino flavour change without the requirement of electron neutrino flux normalization by solar model calculations. It will also provide unusual sensitivity for other measurements of solar neutrino properties, atmospheric neutrinos and supernova neutrinos.

The Sudbury neutrino observatory

The Sudbury Neutrino Observatory (SNO) is a second generation water Čerenkov detector designed to study neutrino astrophysics. We will describe the SNO detector, nearing completion deep underground in INCO's Creighton Mine near Sudbury, Canada and the physics potential of the detector.

Tests of electron flavor conservation with the Sudbury Neutrino Observatory.

We analyze tests of electron flavor conservation that can be performed at the Sudbury Neutrino Observatory (SNO). These tests, which utilize $^8$B solar neutrinos interacting with deuterium, measure: 1) the shape of the recoil electron spectrum in charged-current (CC) interactions (the CC spectrum shape); and 2) the ratio of the number of charged current to neutral current (NC) events (the CC/NC ratio). We determine standard model predictions for the CC spectral shape and for the CC/NC ratio, together with realistic estimates of their errors and the correlations between errors. We consider systematic uncertainties in the standard neutrino spectrum and in the charged-current and neutral current cross-sections, the SNO energy resolution and absolute energy scale, and the SNO detection efficiencies. Assuming that either matter-enhanced or vacuum neutrino oscillations solve the solar neutrino problems, we calculate the confidence levels with which electron flavor non-conservation can be detected using either the CC spectrum shape or the CC/NC ratio, or both. If the SNO detector works as expected, the neutrino oscillation solutions that best-fit the results of the four operating solar neutrino experiments can be distinguished unambiguously from the standard predictions of electron flavor conservation.

The Sudbury Neutrino Observatory electronics chain

The Sudbury Neutrino Observatory (SNO) is a second generation real time solar neutrino water Cherenkov detector using 1000 tonnes of D/sub 2/O viewed by almost 10000 photomultiplier tubes 20 cm in diameter. The electronics chain is required to provide deadtimeless sub-nanosecond time and charge measurement for photomultiplier pulses in the range of 1-1000 photoelectrons. While the solar neutrino event rate is very low, the electronics chain must handle background rates in excess of 1 kHz and burst rates in excess of 1 MHz. The electronics chain is implemented using three full custom integrated circuits and commercial ADCs, memory, and logic. The DAQ interface is VME compatible. We will briefly describe the SNO detector and then concentrate on the design of the electronic system including novel features of the DAQ and trigger paths. >

222Rn emanation into vacuum

A low-background ZnS scintillator cell based on a design by Lucas has been developed for 222Rn detection. Typical cells have 63% detection efficiency and 3 counts per day background. The cells have been used in measurements of 222Rn emanation rate into vacuum from materials to be used under water in the Sudbury Neutrino Observatory (SNO) solar neutrino detector. The results are presented and the impact on the SNO detector design is discussed.