Total Flux Of Active Neutrinos Research Articles

The Sudbury Neutrino Observatory: Observation of Flavor Change for Solar Neutrinos

The Sudbury Neutrino Observatory (SNO) experiment was constructed by an international scientific collaboration primarily to provide a clear determination of whether solar neutrinos change their flavor in transit from the core of the sun to the earth. The detector used 1000 tonnes of heavy water (>99.92% D2O) in an ultra-clean location 2 km underground in INCO's Creighton mine near Sudbury, Canada to observe two separate reactions of neutrinos on deuterium. The first reaction was sensitive only to electron flavor neutrinos and the second reaction was equally sensitive to all neutrino flavors. The measurements by SNO showed clearly that the hypothesis of no neutrino flavor change was ruled out by more than 5.3 standard deviations. The observation of flavor change for neutrinos implies that they have a non-zero mass. The measured total flux of active neutrinos from 8B decay in the sun was found to be in excellent agreement with the predictions of solar model calculations. This paper describes the history and scientific measurements of the SNO experiment.2

The Sudbury Neutrino Observatory: Observation of flavor change for solar neutrinos

The Sudbury Neutrino Observatory (SNO) experiment was constructed by an international scientific collaboration primarily to provide a clear determination of whether solar neutrinos change their flavor in transit from the core of the sun to the earth. The detector used 1000 tonnes of heavy water (>99.92% D2O) in an ultra‐clean location 2 km underground in INCO's Creighton mine near Sudbury, Canada to observe two separate reactions of neutrinos on deuterium. The first reaction was sensitive only to electron flavor neutrinos and the second reaction was equally sensitive to all neutrino flavors. The measurements by SNO showed clearly that the hypothesis of no neutrino flavor change was ruled out by more than 5.3 standard deviations. The observation of flavor change for neutrinos implies that they have a non‐zero mass. The measured total flux of active neutrinos from 8B decay in the sun was found to be in excellent agreement with the predictions of solar model calculations. This paper describes the history and scientific measurements of the SNO experiment.

Measurement of theνeand total8B solar neutrino fluxes with the Sudbury Neutrino Observatory phase-III data set

This paper details the solar neutrino analysis of the 385.17-day Phase-III data set acquired by the Sudbury Neutrino Observatory (SNO). An array of $^3$He proportional counters was installed in the heavy-water target to measure precisely the rate of neutrino-deuteron neutral-current interactions. This technique to determine the total active $^8$B solar neutrino flux was largely independent of the methods employed in previous phases. The total flux of active neutrinos was measured to be $5.54^{+0.33}_{-0.31}(stat.)^{+0.36}_{-0.34}(syst.)\times 10^{6}$ cm$^{-2}$ s$^{-1}$, consistent with previous measurements and standard solar models. A global analysis of solar and reactor neutrino mixing parameters yielded the best-fit values of $\Delta m^2 = 7.59^{+0.19}_{-0.21}\times 10^{-5}{eV}^2$ and $\theta = 34.4^{+1.3}_{-1.2}$ degrees.

Neutrino physics from SNO

The Sudbury Neutrino Observatory (SNO) has completed a combined analysis of the first two phases of the experiment. A detailed description of this analysis was presented at Erice. Details of the analysis have been submitted for publication, and only a brief summary of the paper is included in these proceedings. This analysis, which lowered the energy threshold to an effective kinetic energy threshold of 3.5 MeV, also completely re-evaluated systematic uncertainties and improved them by a factor of two compared to previous published results. The total flux of active neutrinos observed by the neutral current on deuterium, the energy spectrum of electron neutrinos and a combined solar neutrino-KamLAND MSW analysis are presented.

Solar neutrinos, SNO and SNOLAB

The Sudbury Neutrino Observatory is a 1000 tonne heavy water Cherenkov detector situated 2 km underground in INCO's Creighton mine near Sudbury, Ontario, Canada. In the first two phases of the project reported to date, the charged current reaction on deuterium has been used to measure the flux and energy spectrum of solar electron neutrinos and the neutral current reaction has been used to measure the total flux of active neutrinos. Clear evidence of neutrino flavour change has been observed and the total active flux is found to be in agreement with solar model calculations. The experimental third phase with an array of neutron detectors is in progress. The expansion of the underground laboratory to create an international facility known as SNOLAB will be completed in 2007. A number of international experiments for the future detection of lower energy solar neutrinos, geo-neutrinos, dark matter and double beta decay are described.

Recent SNO results and the final SNO phase

The SNO experiment ran in its second phase from 2001 to 2003 with ≈2000 kg of salt added to the heavy water. SNO has recently published 8B flux results and a charged current neutrino spectrum from the full data set of 391 days. The full first two phases of SNO have also been analyzed for periodicities in the solar neutrino signal. Starting in 2003, an array of neutron detectors was added to the SNO experiment to observe the neutral current reaction. Production data taking has been in progress since November 2004. This array will provide an independent measurement of the total flux of active neutrinos from the sun with different systematic uncertainties from the first two phases of SNO. The SNO experiment finishes data taking at the end of 2006 and the heavy water will be returned. A new liquid scintillator experiment (SNO + ) to measure pep solar neutrinos and geo-neutrinos is planned to be build using the SNO detector and infrastructure.

Sudbury Neutrino Observatory Results

The Sudbury Neutrino Observatory uses 1000 tonnes of heavy water in an ultra-clean Cherenkov detector situated 2 km underground in Ontario, Canada to study neutrinos from the Sun and other astrophysical sources. The Charged Current (CC) reaction on deuterium is sensitive only to electron neutrinos whereas the Neutral Current (NC) is equally sensitive to all active neutrino types. By measuring the flux of neutrinos from 8B decay in the Sun with the CC and NC reactions it has been possible to establish clearly, through an appearance measurement, that electron neutrinos change to other active neutrino types, properties that are beyond the Standard Model of elementary particles. The observed total flux of active neutrinos agrees well with solar model flux calculations for 8B. This provides a clear answer to the “Solar Neutrino Problem”. When these results are combined with other measurements, the oscillation of massive neutrinos is strongly defined as the primary mechanism for flavor change and oscillation parameters are well constrained.

RESULTS FROM THE PURE D2O PHASE OF THE SUDBURY NEUTRINO OBSERVATORY

The Sudbury Neutrino Observatory is a 1000 T D2O Cerenkov detector that is sensitive to 8 B and hep solar neutrinos. Both Charged Current and Neutral Current interaction rates on deuterons as well as the Elastic Scattering interaction rate on electrons can be measured simultaneously. Assuming an undistorted 8 B neutrino spectrum, the total flux measured with the NC reaction is [Formula: see text], which is consistent with solar models. The νe component of the 8 B solar flux is [Formula: see text] for a kinetic energy threshold of 5 MeV. The non-νe component is [Formula: see text], which is 5.3σ greater than zero, giving strong evidence for solar νe flavor transformation. The Day-Night Asymmetry for the Charged Current interaction is [Formula: see text]. If the total flux of active neutrinos is additionally constrained to have no asymmetry, the νe asymmetry is found to be [Formula: see text]. Combined with other solar neutrino data, a global MSW oscillation analysis strongly favors the Large Mixing Angle (LMA) solution.

Solar neutrino results from SNO and implications for neutrino oscillations

The SNO experiment has measured the flux of 8B solar neutrinos via CC, NC, and ES interactions in D 2O. The NC flux measurement, φ NC SNO = 5.09 ∮.61 +0.64 × 10 6cm −2s −1, represents the total flux of active neutrinos and is consistent with solar model expectations. When combined with the CC, φ CC rmSNO = 1.76 −0.10 +0.11 × 10 6cm −2s −1, and ES, φ ES SNO = 2.39 = 2.39 −0.26 +0.27 × 10 6cm −2s −1 results, SNO demonstrates the existence of neutrino flavour transformations at the 5.3σ level.

Neutral current and day night measurements from the pure D 2O phase of SNO

The Sudbury Neutrino Observatory is a 1000 T D 2O Cerenkov detector that is sensitive to 8B solar neutrinos. The energy, radius, and direction with respect to the sun is measured for each neutrino event; these distributions are used to separately determine the rates of the charged current, neutral current and electron scattering reactions of neutrinos on deuterium. Assuming an undistorted 8B spectrum, the ν e component of the 8B solar flux is φ e = 1.76 +0.05 −0.05(stat.) +0.09 −0.09 (syst.) × 10 6 cm −2s −1 based on events with a measured kinetic enegy above 5 MeV. The non- ν e component is φ μτ = 3.41 +0.45 −0.45(stat.) +0.48 −0.45 (syst.) × 10 6 cm −2s −1, 5.3 σ greater than zero, providing strong evidence for solar ν e flavor transformation. The total flux measured with the NC reaction is φ NC = 5.09 +0.044 −0.43(stat.) +0.46 −0.43 (syst.) × 10 6 cm −2s −1, consistent with solar models. The night minus day rate is 14.0% ± 6.3% +1.5 −1.4% of the average rate. If the total flux of active neutrinos is additionally constrained to have no asymmetry, the ν e asymmetry is found to be 7.0% ± 4.9% +1.3 −1.2%. A global solar neutrino analysis is terms of matter-enhanced oscillations of two active flavors strongly favors the Large Mixing Angle (LMA) solution.

Constraining the leading weak axial two-body current by recent solar neutrino flux data

We analyze the Sudbury Neutrino Observatory (SNO) and Super-Kamiokande (SK) data on charged current (CC), neutral current (NC) and neutrino electron elastic scattering (ES) reactions to constrain the leading weak axial two-body current parameterized by L_1A. This two-body current is the dominant uncertainty of every low energy weak interaction deuteron breakup process, including SNO's CC and NC reactions. Our method shows that the theoretical inputs to SNO's determination of the CC and NC fluxes can be self-calibrated, be calibrated by SK, or be calibrated by reactor data. The only assumption made is that the total flux of active neutrinos has the standard ^8B spectral shape (but distortions in the electron neutrino spectrum are allowed). We show that SNO's conclusion about the inconsistency of the no-flavor-conversion hypothesis does not contain significant theoretical uncertainty, and we determine the magnitude of the active solar neutrino flux.

First results from the Sudbury Neutrino Observatory

Solar neutrinos from the decay of 8B have been detected at the Sudbury Neutrino Observatory via both charged current (CC) reactions on deuterium and the elastic scattering (ES) of electrons. The flux of electron neutrinos measured with the CC reaction is 1.75±0.07( stat) −0.011 +0.012 ( syst)±0.05( theor) × 10 6 cm −2 s −1. The flux measured with the ES reaction, which can contain contributions from all active neutrino flavors, is 2.39 ±0.34( stat) −0.14 +0.16( syst) × 10 6 cm −2 s −1. There is a 3.3σ difference between the CC flux and the Super-Kamiokande collaboration's precision measurement of the ES flux, strongly suggesting there is a non-electron neutrino component in the solar flux. The same comparison is used to determine that the total flux of active neutrinos from 8B decay is 5.44 ± 0.99 × 10 6 cm −2 s −1, in good agreement with predictions of solar models.

Measurement of day and night neutrino energy spectra at SNO and constraints on neutrino mixing parameters.

The Sudbury Neutrino Observatory (SNO) has measured day and night solar neutrino energy spectra and rates. For charged current events, assuming an undistorted 8B spectrum, the night minus day rate is 14.0%+/-6.3%(+1.5%)(-1.4%) of the average rate. If the total flux of active neutrinos is additionally constrained to have no asymmetry, the nu(e) asymmetry is found to be 7.0%+/-4.9%(+1.3%)(-1.2%). A global solar neutrino analysis in terms of matter-enhanced oscillations of two active flavors strongly favors the large mixing angle solution.