Australian scientists build a secret laboratory in an old gold mine to detect invisible particles

Australia is building a physics lab almost half a mile underground to search for dark matter – the invisible material that outweighs normal matter in the universe. The lab sits in a former gold mine in Stawell, Victoria, and the experiment is called SABRE South.

The goal is simple to say and hard to do. Scientists want to catch a tiny signal that could confirm hints first reported in Italy and finally show what most of the universe is made of.

Building Australia’s dark matter lab

The work is led by Phillip Urquijo, a professor of physics at the University of Melbourne (UNIMELB). His research focuses on the particle nature of dark matter and how to detect it with ultra-low-background sensors.

The underground lab rests about 3,360 feet below the town of Stawell. Thick rock keeps out cosmic rays, high energy particles arriving from space, which can hide the rare events scientists are trying to see.

SABRE South will test a yearly wobble in event rates that one experiment saw decades ago. It will do that in a place far from the Northern Hemisphere labs to rule out seasonal noise.

The site is quiet, dry, and reachable by road, which helps move delicate equipment safely. Clean rooms and strict material screening cut down on stray radiation from the walls and the hardware.

What powers the detector

At the heart of SABRE South are seven sodium iodide crystals – a salt used as a sensor – that flash with faint light when a particle hits an atom. The light is picked up by ultra-sensitive photomultiplier tubes.

The technical design report describes a total target of about 110 pounds. The crystals sit inside roughly 3,170 gallons of liquid for added protection and tagging.

Physicists are chasing a WIMP, a proposed particle that barely interacts with matter. If a WIMP bumps a crystal nucleus, the crystal gives off a tiny flash that rises above the normal sensor noise.

The detector also watches for muons and other fast particles that can fake a signal. Extra veto panels catch those and help toss them out of the data.

Latitude of the dark matter lab

DAMA in Italy claimed to see a yearly signal in sodium iodide. Its latest Phase Two results showed a repeating up-and-down in the lowest energies.

SABRE South sits in the Southern Hemisphere, where seasons are flipped from Italy. If the same annual pattern appears at the same time of year in both places, it points to annual modulation – a yearly up and down in rate, caused by Earth’s motion through the galaxy.

If the pattern flips or fades when seasons swap, that would favor local environmental effects. A matched pair of detectors gives a clean way to sort physics from weather.

Running for several years is crucial because the target signal changes slowly. The team will check not just the timing but also the size and energy shape of any wobble.

Defining a dark matter hit

The design aims for a total background, unwanted signals that can mimic real events, below 0.72 counts per day per kilogram per keV. With that level, SABRE South can either confirm or exclude the Italian claim with strong statistics.

Based on the design report above, two years of data could reach about 5-sigma if the signal is real, or 3-sigma for exclusion if it is not. Here, sigma, a standard measure of statistical certainty, tells you how unlikely a random fluke would be.

Sodium iodide is the same material used in the Italian setup. Matching the target while improving shielding and vetoes keeps the test fair and sharp.

The liquid around the crystals is a scintillator, a liquid that emits light when hit, that tags the telltale gamma rays from trace radioactivity such as potassium-40. When the liquid lights up, scientists can throw out the paired crystal event.

Separating particles from noise

A carefully modeled detector simulation shows how to track every major background source. The study maps what comes from the crystals, the liquid, the steel vessel, and the veto sensors.

Muon paddles span the top of the detector to catch muons, a heavier cousin of the electron, that still sneak through a mile of rock. Their timing helps separate cosmic events from real crystal recoils.

Trace contamination in the crystals is measured and kept extremely low. The design uses ultra-pure powder to reduce potassium and lead daughters that could blur the signal window.

All of these systems work together to lower false alarms. Lower background means fewer doubts about any yearly pattern that appears.

Why particle clues count

“What is out there” is not a vague slogan in this field. The majority of matter in the universe appears to be something new that does not shine and does not absorb light.

“This is testing one of the most enigmatic results or measurements in our field that persistently is showing as a signature consistent with dark matter,” said Urquijo.

If SABRE South sees no annual modulation, it would push researchers to rethink favored WIMP models. If it does see the same pattern with the same phase and energy shape, it would mark a turning point.

Either outcome gives clear guidance for future detectors. The result will steer what masses and interaction strengths are worth the next big push.

Hope for the dark matter lab

Commissioning a low-background detector is slow, careful work. Every part needs testing underground to be sure no stray radiation spoils the data.

The team plans a multi-year run to track a full set of seasons. A steady, repeatable wobble is the hallmark of a real cosmic signal.

Data will come with built-in cross checks. The liquid veto and muon panels give independent views that help confirm the origin of each event.

The broader community is ready to compare notes. Southern and Northern data together will tighten the test and settle a long-running debate.

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