When most of us are revelling in the pleasures of “the dark side” this weekend, particle physicists around the world will be celebrating International Dark Matter Day and contemplating Darkside-20k — a huge dark matter detector under construction in Italy.
Dark matter is often referred to as the invisible “cosmic glue” that makes up most of the mass in the universe and holds galaxies together. According to NASA, it accounts for 27 per cent of the total mass of the universe, while visible matter — the stuff we see around us every day — makes up a mere five per cent. And yet, scientists still aren’t sure what it is or how it works.
The Darkside-20k detector — located deep underground and shielded by 1,400 metres of rock to protect it from cosmic-ray interference — could help solve the mystery. It will look for what are called weakly interacting massive particles (WIMPS), which physicists believe match dark matter’s required traits — heavy mass to exert gravity while completely lacking electromagnetic interactions to stay invisible.
The University of Alberta’s Centre for Particle Physics will play a crucial role in Darkside-20k. Dr. Aksel Hallin and his team are now building a chamber made of more than 10 tonnes of acrylic that will eventually hold the detector’s special non-radioactive liquid argon, a substance that emits light when interacting with WIMPS and allows dark matter to be more accurately studied.
Along with the U of A’s contribution, pieces of the 50-tonne detector are being built around the world by 400 collaborators, says Hallin, and will soon be shipped to Italy for assembly. The whole machine will come together sometime in 2030.
“The research is ultimately driven by curiosity: to better understand the universe,” says Hallin. “It’s a high-priority project globally right now, since we don’t know how dark matter can be used until we know what it is.”
Along with Quantum Horizons Alberta and the Theoretical Physics Institute, the U of A’s Department of Physics is celebrating International Dark Matter Day Oct. 29 and 30 with talks, demonstrations and tours of the observatory and particle physics labs. Admission is free with registration.