Neutrinos are tiny elementary particles, similar to electrons but with no electric charge. They come in three flavours, electron, muon, and tau, and are among the most abundant particles in the universe. They interact with other matter very rarely, which means they can travel through space at nearly the speed of light. Because of this, they can provide valuable information about their sources, earning the nickname ‘messenger particle’.

Ghostly messengers: what neutrinos can tell us

Solar neutrino physics

Solar neutrinos are produced by the same fusion reactions in the sun that produce heat and light. Because the sun is so dense, it takes a million years for the light and heat to travel the 700,000 km from the centre of the sun to its surface (and then 8 minutes for the light to travel to earth). Solar neutrinos interact so rarely that they escape almost immediately, traveling at nearly the speed of light. These solar neutrinos allow astrophysicists to study the core of the sun. At the same time, because the sun produces so many neutrinos (about 60 billion solar neutrinos pass through your thumb nail every second!) they can be used to study neutrino properties. Studying these properties with experiments like SNO+ can help us understand solar fusion, and ultimately the evolution and fate of the sun. These measurements will also test in detail the mechanisms for neutrino flavour oscillations.

Search for neutrinoless double beta decay

One common form of radioactivity is beta decay, where a neutron inside a nucleus changes into a proton, an electron and an antineutrino. However, some atomic nuclei don’t have enough energy to create a proton, electron, and antineutrino. For a few of these nuclei, it is possible to undergo double beta decay, in which the nucleus emits two electrons and two anti-neutrinos at the same time, which requires less energy than beta decay. To date, double beta decay has only been observed in 13 nuclides – this type of decay is very rare. Theoretically, there is a process related to double beta decay called neutrinoless double-beta decay, in which the nucleus emits two electrons and no neutrinos. This can only happen if the two neutrinos that would have normally been emitted by the decaying nucleus annihilate each other. This annihilation could occur if the neutrino is its own antiparticle.  nEXO is one example of a SNOLAB experiment project that is focused on the search for neutrinoless double-beta decay.

Supernova watch

A supernova is the spectacular death of a massive star in an explosion that for a few brief weeks outshines the star’s entire galaxy. When a star goes supernova, neutrinos escape the exploding star before the light emerges, so detecting a burst of neutrinos from a supernova would allow optical astronomers to study the supernova ‘turning on’ long before it would normally be observed. There is a network of neutrino detectors around the world called the Supernova Early Warning System (SNEWS) and, in the event that a burst of neutrinos is detected, SNEWS will alert the astronomy community. The SNO experiment was part of SNEWS, HALO (a designated supernova detector) is part of the network, and SNO+ will also be involved with SNEWS.

Geo neutrinos

Geo-neutrinos are the electron antineutrinos produced by the decay of radioactive materials in the earth – particularly uranium and thorium. Geo-neutrinos were first detected by the KamLAND experiment in Japan. Scientists are interested in geo-neutrinos because they can be used to measure the total amount of heat produced in the earth from radioactivity. Heat from radioactivity is thought to account for between 40% and 100% of the earth’s total heat flux. Because SNOLAB is located in the center of the north american continent, it ‘sees’ a different distribution of geo-neutrinos than what is observed in Japan, making the combined data more useful.

To learn more about neutrinos, check out the neutrino experiments at SNOLAB.