Measurement of the Total Active 8B Solar Neutrino Flux at the Sudbury Neutrino Observatory with Enhanced Neutral Current Sensitivity

Abstract

The Sudbury Neutrino Observatory (SNO) has precisely determined the total active (nu_x) 8B solar neutrino flux without assumptions about the energy dependence of the nu_e survival probability. The measurements were made with dissolved NaCl in the heavy water to enhance the sensitivity and signature for neutral-current interactions. The flux is found to be 5.21 +/- 0.27 (stat) +/- 0.38 (syst) x10^6 cm^{-2}s^{-1}, in agreement with previous measurements and standard solar models. A global analysis of these and other solar and reactor neutrino results yields Delta m^{2} = 7.1^{+1.2}_{-0.6}x10^{-5} ev^2 and theta = 32.5^{+2.4}_{-2.3} degrees. Maximal mixing is rejected at the equivalent of 5.4 standard deviations.

Figures (5)

• Figure 1: (a) Neutron capture efficiency versus source radial position for the pure D$_2$O phase (capture on D) and salt phase (capture on Cl or D) deduced from a ${}^{252}$Cf source, with fits to an analytic function (salt) and to a neutron diffusion model (D$_2$O). (b) Event isotropy from data and Monte Carlo calculations of a ${}^{252}$Cf source and an ${}^{16}$N $\gamma$-ray source.
• Figure 2: Distribution of (a) $\beta_{14}$, (b) $\cos \theta_{\odot}$ and (c) kinetic energy, for the selected events. The CC and ES spectra are extracted from the data using $\beta_{14}$ and $\cos \theta_{\odot}$ distributions in each energy bin. Also shown are the Monte Carlo predictions for CC, ES, NC + internal and external-source neutron events, all scaled to the fit results. The dashed lines represent the summed components. All distributions are for events with $T_{\rm eff}$$\geq$5.5 MeV and R$_{\rm fit}$$\leq$ 550 cm. Differential systematics are not shown.
• Figure 3: Volume-weighted radius ($\rho$) distribution (acrylic vessel=1). Shown are the distributions for CC, ES, NC+internal and external-source neutrons, scaled from the fit, and separately determined external background distributions.
• Figure 4: SNO-only neutrino oscillation contours, including pure D$_2$O day and night spectra, salt CC, NC, ES fluxes, with ${}^{8}$B flux free and hep flux fixed. The best-fit point is $\Delta m^{2}=4.7\times10^{-5}$, $\tan^{2}\theta=0.43$, $f_{B}=1.03$, with $\chi^{2}$/d.o.f.=26.2/34.
• Figure 5: Global neutrino oscillation contours. (a) Solar global: D$_2$O day and night spectra, salt CC, NC, ES fluxes, SK, Cl, Ga. The best-fit point is $\Delta m^2=6.5\times10^{-5}$, $\tan^{2}\theta=0.40$, $f_{B}=1.04$, with $\chi^{2}$/d.o.f.=70.2/81. (b) Solar global + KamLAND. The best-fit point is $\Delta m^2=7.1\times10^{-5}$, $\tan^{2}\theta=0.41$, $f_{B} = 1.02$. In both (a) and (b) the ${}^{8}$B flux is free and the hep flux is fixed.