What happened next: Dark matter lab deep in gold mine

This article is part of a special Cosmos series where our newsroom journalists follow up science from the archive, to find out: What happened next?

In late 2021, I ventured deep into the bowels of a gold mine in regional Victoria to see an unbuilt laboratory. Called the Stawell Underground Physics Laboratory (SUPL). It was designed for a host of scientific experiments, but the principle one was to hold a detector that could confirm or deny our understanding of dark matter.

In the mine the excitement among the science team was palpable. Although the room still looked like a large cave then, but plans and blueprints on the table showed rooms, walls and even showers for the new facility.

At that stage, they had hopes of collecting data from the giant multi-million dollar detector by the end of 2022, and be well on their way to potentially discovering dark matter.

“I was overwhelmed when I went down that tunnel,” says Professor Alan Duffy, Swinburne University of Technology astrophysicist and former lead scientist of the Royal Institution of Australia.

“It was a 45-minute journey to see this huge facility. The roof was over 12 metres high. It’s such a larger space than I imagined, but clearly so full of promise.”

What happened next?

Not much, but it’s starting to build momentum.

“We’ve done a lot of work in the past few years we just didn’t see it all come together. Now it’s going to come together and I’m really happy about that,” says University of Melbourne Professor Phillip Urquijo – a technical coordinator of the detector.

It’s clear talking to him that the enthusiasm is still there.

Delays had pushed back the start date by over a year, and although the team is now hitting small milestones, the bulk of the work of installing the dark matter detector is still yet to come.

Urquijo says there were a number of things that slowed the project. Some of them were technical – like pressure in the lab ensuring that the dusty mine air flows out of the lab rather than in – but one of the biggest issues was continued funding.

Funding for a large project like SUPL doesn’t happen in one chunk. Instead, grant funding needs to be provided year on year, and occasionally, the team doesn’t get funding, which pushes back the start date further. 

“We’re a relatively expensive project for Australian particle physics,” he says.

“Occasionally we get these gaps in time, which are due to paused funding. We have a not-so-reliable funding program for large projects in Australia, particularly for pure science projects.”

The most important first stage, after the science lab itself is built, is the shield. Building it was to start in 2023.

The shield is the final, and bulkiest, part of the dark matter detector. The location – which is a kilometre under the earth – will stop most of the particles that aren’t dark matter from getting through, but the thick steel on the outside of the detector – the shield – will ensure that any stray particles will stay out.

“The shielding is more than 100 tonnes of steel. Fabricating it, and the raw materials and then transporting it to the mine, craning it around – all of these things are, labour intensive, and they require experts,” said Urquijo.

“Every dark matter experiment around the world needs to have a really good background shield. They come in different forms but they’re absolutely essential.”

The second stage of shielding – another few tonnes of steel – is yet to be funded.

The biggest thing about the delay was getting access to the facilities. But now they have it, they have already begun taking the first measurements of muons, a type of subatomic particle similar to an electron.

“Access was a big one. There are various things we couldn’t do until we could bring [the equipment] down to SUPL,” said Urquijo.

“Now that SUPL is open, we have a program of bringing in equipment down. We started with the muons, we’re going to bring down the crystal assembly system. We’re going to be testing and we’re going to have crystals taking data.”

The ‘crystals’ are incredibly pure sodium iodine crystal. This is the heart of the detector – if a particle can get through a kilometre of rock, past the tonnes of steel shielding, and then into the crystal, it’s worth investigating.

But, while the dark matter experiment was slowly coming together, other things have been happening in the background.

A grant has recently been approved for a different type of detector using cryogenic temperatures to detect low mass particles, and for analysing quantum technologies.

The SUPL team will hopefully be receiving data from the dark matter detector by late 2025, Urquijo told me, but in-between then and now there’s plenty of work to do.

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