SNO UK at Oxford

FIRST RESULTS ANNOUNCED - 18 JUNE 2001 See HERE

The Sudbury Neutrino Observatory (SNO) is a UK/Canadian/US experiment, located 2070 m below the surface in shaft number 9 of the INCO Nickel Mine in Sudbury, Ontario. The primary purpose of this experiment is to detect neutrinos from the Sun to investigate the 'Solar Neutrino Problem'. The target for the detection of solar neutrinos is 1000 tonnes of pure heavy water contained in a 12 m diameter acrylic sphere. 

The energy of the Sun and most stars derives from the fusion of protons to form helium nuclei. Some of the steps in this and parallel processes take place through the weak interaction with the emission of electron neutrinos. These solar neutrinos are important as they provide the only direct view of the deep interior of the Sun where the energy is generated, and the Sun is the brightest source of neutrinos available to us.

Five experiments to date have suggested that the electron neutrino flux may be as low as half the expected rate. This is the Solar Neutrino Problem.

If the experiments are correct, then either our understanding of the Sun is seriously wrong, or 'neutrino oscillations', which imply a non-zero neutrino mass, are reducing the terrestrial flux of electron neutrinos in favour of other neutrinos which cannot be identified by existing experiments.

SNO will be able to detect electron neutrinos via a charged-current interaction with much higher sensitivity than existing experiments, and to detect all three types of neutrino via a neutral-current interaction. It is the ability to detect muon and tau neutrinos equally as well as electron neutrinos that uniquely makes possible an explicit oscillation measurement which is sensitive to small neutrino masses (down to the order of microelectronvolts).

Neutrino data taking started in 1999. The first phase of running with pure heavy water, primarily to measure the charged-current signal, was completed in May 2001. Salt has been added for the next phase to improve the sensitivity to the neutral-current signal.

Computer Simulation and Analysis

Oxford carries the central responsibility for computer simulation and analysis. Methods for analysing the data have been developed using both computer simulation of events and experimental measurements of the characteristics of the critical components of the Cerenkov counter. The custom-built software package SNOMAN is used for this purpose.

Purification Techniques

Oxford has conducted research into the purification of the water down to the level of one decay per ton per day, and has developed a technique to extract thorium, radium and lead using ultra-filtration membranes coated with hydrous titanium oxide. The activity is measured by using beta-alpha coincidence counting. This level of purity is required to reduce the background to the neutral current signal to an insignificant level. 

Some pictures of SNO.

See the main SNO page at Queens.

Return to the Oxford Neutrino page.