Sudbury Neutrino Observatory

Beyond the Standard Model
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Experiments ANNIE Gran Sasso INO LHC SNO Super-K Tevatron NOvA
v t e

The Sudbury Neutrino Observatory (SNO) was a

The director of the experiment, Art McDonald, was co-awarded the Nobel Prize in Physics in 2015 for the experiment's contribution to the discovery of neutrino oscillation.^[1]

The underground laboratory has been enlarged into a permanent facility and now operates multiple experiments as SNOLAB. The SNO equipment itself was being refurbished as of February 2017^[update] for use in the SNO+ experiment.

The first measurements of the number of solar neutrinos reaching the Earth were taken in the 1960s, and all experiments prior to SNO observed a third to a half fewer neutrinos than were predicted by the

The Creighton Mine in Sudbury is among the deepest in the world and, accordingly, experiences a very small background flux of radiation. It was quickly identified as an ideal place for Chen's proposed experiment to be built,[3] and the mine management was willing to make the location available for only incremental costs.^[5]: 440

The SNO collaboration held its first meeting in 1984. At the time it competed with

The experiment observed the light produced by

The SNO detector target consisted of 1,000

In the neutral current interaction, a neutrino dissociates the deuteron, breaking it into its constituent neutron and proton. The neutrino continues on with slightly less energy, and all three neutrino flavours are equally likely to participate in this interaction. Heavy water has a small cross section for neutrons, but when neutrons are captured by a deuterium nucleus, a gamma ray (photon) with roughly 6 MeV of energy is produced. The direction of the gamma ray is completely uncorrelated with the direction of the neutrino. Some of the neutrons produced from the dissociated deuterons make their way through the acrylic vessel into the light water jacket surrounding the heavy water, and since light water has a very large cross section for neutron capture, these neutrons are captured very quickly. Gamma rays of roughly 2.2 MeV are produced in this reaction, but because the energy of the photons is less than the detector's energy threshold (meaning they do not trigger the photomultipliers), they are not directly observable. However, when the gamma ray collides with an electron via Compton scattering, the accelerated electron can be detected through Cherenkov radiation.

In the

The first scientific results of SNO were published on 18 June 2001,^[8][9] and presented the first clear evidence that neutrinos oscillate (i.e. that they can transmute into one another), as they travel from the Sun. This oscillation, in turn, implies that neutrinos have non-zero masses. The total flux of all neutrino flavours measured by SNO agrees well with theoretical predictions. Further measurements carried out by SNO have since confirmed and improved the precision of the original result.

Although Super-K had beaten SNO to the punch, having published evidence for neutrino oscillation as early as 1998, the Super-K results were not conclusive and did not specifically deal with solar neutrinos. SNO's results were the first to directly demonstrate oscillations in solar neutrinos. This was important to the

• Carleton University
• Laurentian University
• Queen's University – designed and built many calibration sources and the device for deploying sources
• TRIUMF
• University of British Columbia
• University of Guelph

Although no longer a collaborating institution, Chalk River Laboratories led the construction of the acrylic vessel that holds the heavy water, and Atomic Energy of Canada Limited was the source of the heavy water.

• University of Oxford – developed much of the experiment's Monte Carlo analysis program (SNOMAN), and maintained the program
• University of Sussex – calibration

• Lawrence Berkeley National Laboratory (LBNL) – Led the construction of the geodesic structure that holds the PMTs
• Pacific Northwest National Laboratory (PNNL)
• Los Alamos National Laboratory (LANL)
• University of Pennsylvania – designed and built the front end electronics and trigger
• University of Washington – designed and built proportional counter tubes for detection of neutrons in the third phase of the experiment
• Brookhaven National Laboratory
• University of Texas at Austin
• Massachusetts Institute of Technology

• 14724 SNO
  is named in honour of SNO.
• In November 2006, the entire SNO team was awarded the inaugural John C. Polanyi Award for "a recent outstanding advance in any field of the natural sciences or engineering" conducted in Canada.^[12]
• SNO principal investigator Arthur B. McDonald won the 2015 Nobel Prize in Physics, jointly with Takaaki Kajita of Super-Kamiokande, for the discovery of neutrino oscillation.
• SNO was awarded the 2016
  Fundamental Physics Prize
  along with 4 other neutrino experiments.

• DEAP – Dark Matter Experiment using Argon Pulse-shape at SNO location
• Homestake experiment – A predecessor experiment conducted 1970–1994 in a mine at Lead, South Dakota
• SNO+ – The successor of SNO
• SNOLAB – A permanent underground physics laboratory being built around SNO

46°28′30″N 81°12′04″W / 46.47500°N 81.20111°W / 46.47500; -81.20111^[13]