As Australian researchers prepare for the SABRE South dark matter experiment to begin, The Innovation Platform spoke with the project’s lead, Professor Phillip Urquijo, to find out what the future research could mean for our understanding of dark matter and the Universe as a whole
Still one of the Universe’s most elusive phenomena, dark matter is an invisible, hypothetical form of matter that does not emit, absorb, or reflect light, making it invisible to current telescopes. Scientists know it exists because of its gravitational effects on visible matter, such as the way galaxies rotate and how light bends around massive objects. Although it cannot be directly observed, dark matter is thought to make up about 85% of all matter in the Universe. Understanding what dark matter is made of remains one of the biggest challenges in modern astrophysics.
Now, scientists in Australia have taken a major step forward in the hunt for dark matter, obtaining research results that will allow them to start a new world-class experiment later this year. Researchers from the ARC Centre of Excellence for Dark Matter Particle Physics recorded muon – or cosmic radiation – levels inside and outside the Stawell Underground Physics Laboratory (SUPL) over the course of a year. They detected 30,000 muons inside the underground laboratory, while 8.4 billion muons would be expected to be detected on the surface of the Earth – measurements low enough to host the SABRE South dark matter experiment. The muons that reach SUPL are produced in the atmosphere with as much (and sometimes much more) energy as in the collisions of the large hadron collider at CERN.
SUPL was constructed in the Stawell Gold Mine in 2022 to house the SABRE South dark matter experiment and other research requiring deep underground conditions. It is the first facility of its kind in the Southern Hemisphere, placing Australia firmly on the world stage as a centre for science. The SABRE South experiment mirrors a similar experiment undertaken in Italy called the DAMA/LIBRA, which detected signals that scientists believe could be dark matter.
To find out more about what the experiment will look like and what implications the research could have for our understanding of the Universe, we spoke to the project’s lead, Professor Phillip Urquijo.
How long has it taken to reach this starting point for the SABRE South experiment? Did you have to overcome any obstacles to get to this stage?
This has been the better part of a decade in the making. SUPL sits 1 km underground in the Stawell Gold Mine, where the rock overburden gives almost 3 km of water-equivalent shielding. That suppresses the cosmic ray muons which flood detectors at the surface, down to a level comparable with established laboratories like Boulby and Kamioka.
Earlier this year, we published the first direct measurement of the underground cosmic muon flux at SUPL (G. Fu et al., Astropart. Phys. 179 (2026) 103240). I led the work, with the analysis driven in particular by several of my PhD students and postdocs, notably Guangyong Fu and Mike Mews. We used the eight plastic scintillator panels that make up the SABRE South muon veto, assembled in a telescope configuration, and measured a flux of about 6.3 x 10-8 per square centimetre per second. That agrees well with our simulations and confirms the overburden brings the muon rate down to what a rare-event search needs. The veto was the first major detector system we put into SUPL, in early 2024, so the measurement doubled as an in-situ test of our data acquisition and processing.
The muon rate is only one piece of the background picture, though, and not the hardest one. The bigger, longer-running job is radioactivity. To get the lab and the detector to the sensitivity we need, every component near the crystals has to be screened for trace radioactive contaminants, because at these sensitivities even minute amounts in the surrounding materials can swamp the signal. On top of that, there are the practical demands of building a low-background laboratory inside a working mine, which means a lot of careful coordination on access, ventilation, cleanliness, and infrastructure. Getting the clean room, shielding, and assembly procedures all up to standard has taken a sustained effort from a large team.
How will the SABRE South experiment build on previous, similar experiments?
SABRE South follows a result that has been unresolved for over two decades. The DAMA/LIBRA experiment in Italy reported an annual modulation in its event rate – a yearly rise and fall of the sort you would expect as the Earth moves through the galaxy’s dark matter halo. The problem is that no experiment using a different target material has confirmed or refuted it, and the signal is in tension with those null results.
What sets SABRE apart is that we use the same target as DAMA, sodium iodide, so it is a genuine like-for-like test rather than a comparison across different technologies. We have also pushed our crystals’ radio-purity beyond what DAMA achieved and surrounded them with an active veto to reject backgrounds. SABRE South runs in the Southern Hemisphere while a companion experiment runs in the north, and that lets us tell a true dark matter signal apart from local seasonal effects. A genuine modulation should look the same in both hemispheres, whereas anything seasonal would flip. The muon flux phase (seasonal peak) is different on the surface compared to deep underground, and depends on atmospheric column density changes through the year.
We also have a new result coming out soon where we measure the muon flux angular distribution, which further constrains our understanding of cosmic ray background to dark matter searches in SUPL.
What will be the key goals of the SABRE experiment when it commences taking data?
The first priority once we start taking data is the detector itself: calibrating it carefully and making sure we understand exactly how it responds, so we can trust what it tells us. We will use blinded analysis techniques, where the region of the data that holds the potential signal is kept hidden until the analysis is finalised, so that our choices cannot bias the result. Underpinning all of this is the goal of operating the best detector of its kind in the world, with the radio-purity, background control and stability that a measurement this delicate demands.
The central physics goal is to test the DAMA annual modulation claim using the same target material. If we see the modulation, it points toward dark matter and would be a remarkable confirmation. If we do not, it resolves a longstanding anomaly and rules out the most straightforward dark matter reading of DAMA’s result. Both outcomes are scientifically decisive, which is what makes the measurement worth doing. Beyond that, it establishes Australia’s ability to carry out world-leading low-background physics.
Will you be collaborating with international researchers and organisations for the experiment?
Yes, extensively. SABRE has a core collaboration across Australia, Italy, and the United States. We also work closely with institutions in the UK, Japan, and China, particularly on the radiation screening and crystal production capabilities we do not yet have in Australia. This is not science you do as a single institution; the collaboration pulls together crystal growth, detector design, background modelling, and analysis expertise from around the world.
What does it mean to have an experiment like this in Australia?
A great deal. SUPL is Australia’s first deep underground physics laboratory, and SABRE South is its flagship experiment – the first major large-scale particle physics experiment of its kind to be led from Australia. For most of our field’s history, Australian researchers have had to join offshore-led projects in the Northern Hemisphere, so being able to lead one from home soil is a real shift. It gives our researchers and students that opportunity, and it builds national infrastructure and expertise that will last. The Southern Hemisphere location also happens to be a scientific asset, since it is what lets the global effort separate a real dark matter signal from seasonal effects.
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