Underneath Lively, Ontario lies the world’s deepest underground clean laboratory. SNOLAB, located two km under the Earth’s surface, held its official grand opening on May 17th. This facility aims to explain mysteries in the field of astroparticle physics with a focus in dark matter and neutrinos. It is an expansion of the old Sudbury Neutrino Observatory (SNO) experiment that, in 2002, solved the solar neutrino problem. Its findings provided strong evidence for neutrino flavour oscillations.
Now, 10 years later, the laboratory has been expanded to allow for more experiments. Most notably is the construction of SNO+. This experiment utilizes the same support structure and acrylic vessel as the SNO experiment. By replacing the Cherenkov heavy water with scintillating linear alkylbenzene, SNO+ will have a much higher sensitivity to low energy neutrinos propagating from the Sun.
Neutrinos are near massless particles that interact only by the weak nuclear force. Since neutrinos do not interact electromagnetically, they are unaffected by the ionic plasma atmosphere of stellar objects. Most other particles, including photons, are trapped within this field. This makes neutrinos the only viable candidate for probing the interior of stellar objects.
In addition, neutrino detection also offers advanced detection of supernovae. An enormous amount of visible light is produced during the collapse of a massive star; often, this is observable with amateur telescopes. Despite this only about 1% of the energy released during a supernova is in the form of photons and the kinetic energy of the expanding remnants. The remaining energy is in the form of neutrinos. Furthermore, neutrinos will propagate faster than light because of its non-electromagnetic interactions. The Helium And Lead Observatory (HALO) experiment at SNOLAB is a newly operational supernovae detector, which is a part of the SuperNova Early Warning System (SNEWS). SNEWS is an international network of neutrino detectors providing astronomers early warning of supernovae event.
The other focus of SNOLAB deals with the detection of dark matter. From astronomical observations there is very strong evidence for the existence of dark matter. By observing the orbital velocities of local galaxies, it was found that the orbits were much too fast from the gravitational forces of the visible cluster. Gravitational lensing observations of galactic clusters confirm the same hypothesis; there is not enough visible matter. It is theorized that only about 4% of the Universe is composed of atoms. The remaining is in dark matter (24%) and dark energy (72%).
There are currently two dark matter detectors collecting data at SNOLAB and two additional large scale dark matter detectors under construction. As our solar system orbits with the Milky Way, it will pass through clusters of dark matter. Since dark matter interacts very weakly with regular matter it is very difficult to detect. The DEAP-1 and COUPP dark matter detectors use very different methodologies to detect dark matter. DEAP-1 uses liquid argon as a scintillator, which emits UV light during an interaction. The UV light can be detected with photomultiplier tubes (PMTs). COUPP is a bubble chamber which uses super heated liquid as its detection medium. When a dark matter particle strikes the nucleus of an atom in the liquid, a bubble of vapour will form. The sound that this bubble makes can be picked up with piezoelectric transducers.
SNOLAB is at the forefront of astroparticle physics research. Studying neutrinos and dark matter will allow us a greater understanding of the Universe. It is hard for us to see the practical benefits of these experiments, but who know? Sooner or later practical applications will emerge, like it did for the nucleus.
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