No abstract

Results are reported from a joint analysis of Phase I and Phase II data from the Sudbury Neutrino Observatory. The effective electron kinetic energy threshold used is T eff = 3.5 MeV, the lowest analysis threshold yet achieved with water Cherenkov detector data. In units of 10 6 cm −2 s −1 , the total flux of active-flavor neutrinos from 8 B decay in the Sun measured using the neutral current (NC) reaction of neutrinos on deuterons, with no constraint on the 8 B neutrino energy spectrum, is found to be NC = 5.140 +0.160 −0.158 (stat) +0.132 −0.117 (syst). These uncertainties are more than a factor of 2 smaller than previously published results. Also presented are the spectra of recoil electrons from the charged current reaction of neutrinos on deuterons and the elastic scattering of electrons. A fit to the Sudbury Neutrino Observatory data in which the free parameters directly describe the total 8 B neutrino flux and the energy-dependent ν e survival probability provides a measure of the total 8

The Sudbury Neutrino Observatory (SNO) used an array of 3 He proportional counters to measure the rate of neutral-current interactions in heavy water and precisely determined the total active (ν x ) 8 B solar neutrino flux. This technique is independent of previous methods employed by SNO The Sudbury Neutrino Observatory [1] detects 8 B solar neutrinos through three reactions: charged-current interactions (CC) on deuterons, in which only electron neutrinos participate; neutrino-electron elastic scattering (ES), which are dominated by contributions from electron neutrinos; and neutral-current (NC) disintegration of the deuteron by neutri-

Tests on B − L symmetry breaking models are important probes to search for new physics. One proposed model with ΔðB − LÞ ¼ 2 involves the oscillations of a neutron to an antineutron. In this paper, a new limit on this process is derived for the data acquired from all three operational phases of the Sudbury Neutrino Observatory experiment. The search concentrated on oscillations occurring within the deuteron, and 23 events were observed against a background expectation of 30.5 events. These translated to a lower limit on the nuclear lifetime of 1.48 × 10 31 yr at 90% C.L. when no restriction was placed on the signal likelihood space (unbounded). Alternatively, a lower limit on the nuclear lifetime was found to be 1.18 × 10 31 yr at 90% C.L. when the signal was forced into a positive likelihood space (bounded). Values for the free oscillation time derived from various models are also provided in this article. This is the first search for neutron-antineutron oscillation with the deuteron as a target.

A search has been made for neutrinos from the hep reaction in the Sun and from the diffuse supernova neutrino background ( DSNB) using data collected during the first operational phase of the Sudbury Neutrino Observatory, with an exposure of 0.65 ktons yr. For the hep neutrino search, two events are observed in the effective electron energy range of 14:3 MeV < T eA < 20 MeV, where 3.1 background events are expected. After accounting for neutrino oscillations, an upper limit of 2:3 ; 10 4 cm À2 s À1 at the 90% confidence level is inferred on the integral total flux of hep neutrinos. For DSNB neutrinos, no events are observed in the effective electron energy range of 21 MeV < T eA < 35 MeV, and, consequently, an upper limit on the e component of the DSNB flux in the neutrino energy range of 22:9 MeV < E < 36:9 MeVof 70 cm À2 s À1 is inferred at the 90% confidence level. This is an improvement by a factor of 6.5 on the previous best upper limit on the hep neutrino flux and by 2 orders of magnitude on the previous upper limit on the e component of the DSNB flux.