Sudbury Neutrino Observatory Research Articles

Constraints on two-body axial currents from reactor antineutrino–deuteron breakup reactions

We discuss how to reduce theoretical uncertainties in the neutrino–deuteron breakup cross-sections crucial to the Sudbury Neutrino Observatory's efforts to measure the solar neutrino flux. In effective field theory, the dominant uncertainties in all neutrino–deuteron reactions can be expressed through a single, common, isovector axial two-body current parameterized by L1,A. After briefly reviewing the status of fixing L1,A experimentally, we present a constraint on L1,A imposed by existing reactor antineutrino–deuteron breakup data. This constraint alone leads to an uncertainty of 6–7% at 7 MeV neutrino energy in the cross-sections relevant to the Sudbury Neutrino Observatory. However, more significantly for the Sudbury experiment, the constraint implies an uncertainty of only 0.7% in the ratio of charged to neutral current cross-sections used to verify the existence of neutrino oscillations, at the same energy. This is the only direct experimental constraint from the two-body system, to date, of the uncertainty in these cross-sections.

Inverting a supernova: neutrino mixing, temperatures and binding energy

We show that the temperatures of the emergent non-electron neutrinos and the binding energy released by a galactic Type II supernova are determinable, assuming the Large Mixing Angle (LMA) solution is correct, from observations at the Sudbury Neutrino Observatory (SNO) and at Super-Kamiokande (SK). If the neutrino mass hierarchy is inverted, either a lower or upper bound can be placed on the neutrino mixing angle θ13, and the hierarchy can be deduced for adiabatic transitions. For the normal hierarchy, neither can θ13 be constrained nor can the hierarchy be determined. Our conclusions are qualitatively unchanged for the proposed Hyper-Kamiokande detector.

Direct observation of neutrino oscillations at the Sudbury Neutrino Observatory

A brief description of the path-breaking evidence for the observation of neutrino oscillations at the Sudbury Neutrino Observatory is presented and the experimental principles and theory thereof are briefly discussed.

SOLAR NEUTRINO RESULTS FROM THE SUDBURY NEUTRINO OBSERVATORY

We describe here the measurement of the flux of neutrinos created by the decay of solar 8B by the Sudbury Neutrino Observatory (SNO). The neutrinos were detected via the charged current (CC) reaction on deuterium and by the elastic scattering (ES) of electrons. The CC reaction is sensitive exclusively to νe's, while the ES reaction also has a small sensitivity to νμ's and ντ's. The flux of νe's from 8B decay measured by the CC reaction rate is [Formula: see text]. Assuming no flavor transformation, the flux inferred from the ES reaction rate is [Formula: see text]. Comparison of ϕ CC (νe) to the Super-Kamiokande Collaboration's precision value of ϕ ES (νx) yields a 3.3σ difference, assuming the systematic uncertainties are normally distributed, providing evidence that there is non-electron flavor active neutrino component in the solar flux. The total flux of active 8B neutrinos is thus determined to be 5.44 ± 0.99 × 106 cm- 2s- 1, in close agreement with the predictions of solar models.

CONCLUDING REMARKS

Important new results have been presented at this conference. The direct violation of CP in K0 → π + π has been firmly established in two independent experiments, NA48 at CERN and KTeV at Fermilab. Both Babar at SLAC and Belle at Kek have determined the CP violation in [Formula: see text] oscillations through the study of the golden KS + Ψ decay mode. The observed CP violation agrees with the expectations of the Standard model, based on the quark-mixing phenomenon. The first results of the Sudbury Neutrino Observatory, SNO, suggest that the long-lasting solar neutrino puzzle has been finally solved in terms of neutrino oscillations. Results appeared after the conference which modify the theoretical prediction of the muon anomaly. This new result, if confirmed, would drastically reduce the significance of the discrepancy between the theoretically expected value for the muon anomaly and the recent results of the Brookhaven experiment.

Seismic Test of Solar Models, Solar Neutrinos, and Implications for Metal‐rich Accretion

The Sun is believed to have been the recipient of a substantial amount of metal-rich material over the course of its evolution, particularly in the early stages of the solar system. With a long diffusion timescale, the majority of this accreted matter should still exist in the solar convection zone, enhancing its observed surface abundance, and implying a lower abundance core. While helioseismology rules out solar models with near-zero metallicity cores, some solar models with enhanced metallicity in the convection zone might be viable, as small perturbations to the standard model. Because of the reduced interior opacity and core temperature, the neutrino flux predicted for such models is lower than that predicted by the standard solar model. This paper examines how compatible inhomogeneous solar models of this kind are with the observed low and intermediate degree p-mode oscillation data, and with the solar neutrino data from the Sudbury Neutrino Observatory Collaboration. We set an upper limit on how much metal-rich accretion took place during the early evolution of the Sun at ~2 M⊕ of iron (or ~40 M⊕ of meteoric material).

Solar neutrino results from the sudbury neutrino observatoryy

Solar neutrinos from the decay of 8B have been detected at the Sudbury Neutrino Observatory (SNO) via the charged-current (CC) reaction on deuterium and the elastic scattering (ES) of electrons. The CC reaction is sensitive exclusively to electron neutrinos while the ES reaction also has a small sensitivity to muon and tau neutrinos. The flux of electron neutrinos from 8B decays measured by the CC reaction and ES reaction, assuming no flavour transformation, will be presented. These flux measurements provide evidence that there is a non-electron flavour active neutrino component in the solar flux. The total flux of active 8B neutrinos will be presented and shown to be in good agreement with predictions of solar models.

Phenomenology of neutrino oscillations

We review the status of several phenomenological topics of current interest in neutrino oscillations: (i) Solar neutrino oscillations after the first Sudbury Neutrino Observatory measurements, including both model-independent and model-dependent results; (ii) Dominant ν μ → ν τ oscillations of atmospheric and K2K neutrinos, and possible subdominant oscillations induced by either extra states or extra interactions; and (iii) Four-neutrino scenarios embedding the controversial LSND evidence for oscillations.

Detectability of the supernova relic neutrinos and neutrino oscillation

We investigate the flux and the event rate of the supernova relic neutrino (SRN) background at the SuperKamiokande (SK) detector for various neutrino oscillation models with parameters inferred from recent experimental results. A realistic model of neutrino emission from supernova explosions and several models of the cosmic star formation history are adopted in the calculation. The number flux over entire energy range is found to be 11–15 cm −2 s −1. We discuss the detection possibility of SRN at SK, comparing this SRN flux with other background neutrinos in more detail than previous studies. Even though there is no energy window in which SRN is dominant, we might detect it as the distortion of the other background event. We found in the energy range 17–25 MeV the expected event rate at SK 0.4–0.8 yr −1. In this range, ten-year observation might enable us to detect SRN signal (at one sigma level) in the case of LMA solar neutrino solution. We also investigate event rate at Sudbury Neutrino Observatory (SNO) and KamLAND. Although we can find energy window, the expected event rate is rather small (0.03 yr −1 for SNO, 0.1 yr −1 for KamLAND).

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.

Direct Evidence for Neutrino Flavor Transformation from Neutral-Current Interactions in the Sudbury Neutrino Observatory

Observations of neutral-current nu interactions on deuterium in the Sudbury Neutrino Observatory are reported. Using the neutral current (NC), elastic scattering, and charged current reactions and assuming the standard 8B shape, the nu(e) component of the 8B solar flux is phis(e) = 1.76(+0.05)(-0.05)(stat)(+0.09)(-0.09)(syst) x 10(6) cm(-2) s(-1) for a kinetic energy threshold of 5 MeV. The non-nu(e) component is phi(mu)(tau) = 3.41(+0.45)(-0.45)(stat)(+0.48)(-0.45)(syst) x 10(6) cm(-2) s(-1), 5.3sigma greater than zero, providing strong evidence for solar nu(e) flavor transformation. The total flux measured with the NC reaction is phi(NC) = 5.09(+0.44)(-0.43)(stat)(+0.46)(-0.43)(syst) x 10(6) cm(-2) s(-1), consistent with solar models.

A three-dimensional calculation of atmospheric neutrino fluxes

We present a three-dimensional (3-D) calculation of atmospheric neutrino fluxes using accurate models of the geomagnetic field, hadronic interactions, tracking and decays. Results are presented for the Super-Kamiokande and Sudbury Neutrino Observatory sites using the GEANT-FLUKA hadronic code. We make a comparison with previous one-dimensional calculations and other 3-D results. The recently reported geometrical enhancement of low energy, horizontal neutrinos is confirmed. The effect on observed leptons is however, restricted to a small overall increase in flux. We report east–west asymmetries for each of the neutrino species.

Addendum to “Model-dependent and -independent implications of the first Sudbury Neutrino Observatory results”

In the light of recent experimental and theoretical improvements, we review our previous model-independent comparison [hep-ph/0106247] of the Super-Kamiokande (SK) and Sudbury Neutrino Observatory (SNO) solar neutrino event rates, including updated values for the ``equalized'' SK datum and for the reference Standard Solar Model (SSM) B neutrino flux. We find that the joint SK+SNO evidence for active neutrino flavor transitions is confirmed at the level of 3.3 standard deviations, independently of possible transitions to sterile states. Barring sterile neutrinos, we estimate the 3-sigma range for the $^8$B neutrino flux (normalized to SSM) as f_B=0.96 +0.54-0.55. Accordingly, the 3-sigma range for the energy-averaged nu_e survival probability is found to be <P_ee> = 0.31 +0.55-0.16, independently of the functional form of P_ee. An increase of the reference nu_e + d --> p + p + e cross section by ~3%, as suggested by recent theoretical calculations, would slightly shift the central values of f_B and of <P_ee> to ~1.00 and ~0.29, respectively, and would strengthen the model-independent evidence for nu_e transitions into active states at the level of ~3.6 sigma.

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.

Implications of recent solar neutrino observations: An analysis of charged current data

We have analysed the recent results from the observation of charged current \nu_e d \to e^- p p events from solar neutrinos by the Sudbury Neutrino Observatory SNO assuming neutrino oscillations with three active flavours. The data seem to prefer a low mass-squared difference and large mixing angle solution (the so-called LOW solution) in (12) parameter space. However, when combined with the Gallium charged current interaction data from Gallex and GNO, distinct (1\sigma) allowed regions corresponding to the large mixing angle (LMA) and small mixing angle (SMA) appear while the LOW solution is disfavoured upto 3\sigma standard deviation. The physical electron neutrino survival probability corresponding to these best fit solutions are then determined and analysed for their energy dependence.

Neutrino masses from three-body decays

Recent neutrino oscillation experiments have presented evidence for very small Δm 2 (eV 2)⪡1 which, if confirmed by independent experiments, can be interpreted in two different ways, namely in terms of a hierarchical neutrino mass scale but also in terms of a (near) neutrino mass degeneracy m ν τ ≈ m ν μ ≈ m ν e ≡ m ν . In the latter case direct neutrino mass determinations are called for to determine the value of m ν . Very recent data from the Sudbury Neutrino Observatory limit neutrino masses to 0.05 eV<∑ m ν i <8.4 eV which still allows m ν -values in the eV-range. We therefore take a fresh look at the principle sensitivity of weak three-body decays w.r.t. a nonvanishing neutrino mass of that order. The position of the point on the upper Dalitz plot boundary for which the final state (massive) neutrino is at rest is shown to be linearly sensitive to m ν . We present and discuss various analytical results for tritium decay, free neutron decay, pion radiative decay and tauon semi-leptonic decay.

Solar neutrino results from the sudbury neutrino observatory

Solar neutrinos from the decay of 8B have been detected at the Sudbury Neutrino Observatory (SNO) via the charged-current (CC) reaction on deuterium and by the elastic scattering (ES) of electrons. The CC reaction is sensitive exclusively to electron neutrinos while the ES reaction also has a small sensitivity to muon and tau neutrinos. In addition, SNO has the capability to provide a measurement of the flux of all active neutrino flavours via the neutral-current (NC) reaction on deuterium. The flux of electron neutrinos from 8B decays measured by the CC reaction and the flux of the ES reaction, assuming no flavour transformation, will be presented. These flux measurements provide evidence that there is a non-electron flavour active neutrino component in the solar flux. The total flux of active 8B neutrinos will be presented and shown to be in good agreement, with predictions of solar models.

Neutrino Burst from Supernovae and Neutrino Oscillation

Neutrino bursts from core-collapse driven supernovae are the most luminous neutrino sources in the universe. If neutrinos have finite masses and convert each other, the time profile and energy spectrum of the burst are greatly modified. We review how this conversion happens in a supernova mantle, and how the burst will be detected by SK (Super-Kamiokande) and SNO (Sudbury Neutrino Observatory) if a supernova appears at the Galactic center. We show that the degeneracy of the solar neutrino problem can be broken by the combination of the SK and SNO detections of a future Galactic supernova. We also discuss effects of neutrino oscillation on the determination of the supernova direction by neutrino observations, and on the supernova relic neutrino observations.

SNO results and neutrino magnetic moment solution to the solar neutrino problem

We have analysed the solar neutrino data obtained from chlorine, gallium and Super-Kamiokande (SK) experiments (1258 days) and also the new results that came from Sudbury Neutrino Observatory (SNO) charge current (CC) and elastic scattering (ES) experiments considering that the solar neutrino deficit is due to the interaction of neutrino transition magnetic moment with the solar magnetic field. We have also analysed the moments of the spectrum of scattered electrons at SK. Another new feature in the analysis is that for the global analysis, we have replaced the spectrum by its centroid.

Unknowns after the SNO Charged-Current Measurement

We perform a model-independent analysis of solar neutrino flux rates including the recent charged-current measurement at the Sudbury Neutrino Observatory (SNO). We derive a universal sum rule involving SNO and SuperKamiokande rates, and show that the SNO neutral-current measurement cannot fix the fraction of solar nu(e) oscillating to sterile neutrinos. The large uncertainty in the standard solar model (8)B flux impedes a determination of the sterile neutrino fraction.