The search for dark matter has led to the Large Hadron Collider (nothing yet) and to deep black corners of outer space (inconclusive). Where should scientists look next? If you said, “In an Australian gold mine,” you must own an Australian gold mine and are looking for ways to make it pay for itself once the gold runs out. Or you’ve heard about the Stawell Underground Physics Laboratory (SUPL) that is setting up a dark matter detector in the Stawell Gold Mine in Victoria in January 2017.
Why look for dark matter in the Stawell Gold Mine? For starters, because it’s deep, dark and accessible. A 15 km (9.3 mile) tunnel leads to a 10-by-35 meter (33-by-115 ft.) open area carved into solid rock and reinforced with bolts and concrete. The miles of solid rock above it will keep cosmic rays from interfering with the southern half of the SABRE (Sodium-iodide with Active Background REjection) detector. SABRE is an “incredibly pure” crystal of sodium iodide which will emit a flash of light when dark matter collides with the nucleus of one of its atoms.
The northern half of the experiment is already operational in the underground Gran Sasso laboratory in Italy which uses thallium-doped sodium iodide crystals that also give off light when hit by dark matter. In fact, that actually there as part of the DAMA (Dark Matter)-LIBRA experiment, a predecessor to SABRE.
Unfortunately, that detection was deemed inconsistent because of a phenomenon known as “annual modulation.” The amount of dark matter around Earth is expected to change as the planet orbits the Sun, causing a seasonal variation in collisions. DAMA-LIBRA saw this but more sensitive dark matter detectors in other labs (LUX and XENON) have not. Putting a second SABRE detector in the southern hemisphere should allow the researchers to rule out differences caused by seasonal variations.
That’s the theory. We’ll find out if dark matter really does exist in Australian gold mines when the SABRE experiment begins operation in the Stawell Gold Mine in late 2017.