Jacinta Bowler
Jacinta Bowler is a science journalist at Cosmos.
They were published in the Best Australian Science Writing 2023.
Physicists have a problem – a neutrino problem. On Monday, seventy of the globe’s brightest minds in dark matter will come together to help shape the field’s future, and find a solution to the issue of ‘neutrino fog’.
“We have a lot of experiments all around the world, which are trying to detect dark matter in deep underground laboratories,” Dr Ciaran O’Hare, University of Sydney researcher and one of the organisers of the event, told Cosmos.
“But there are problems. I mean, namely the fact that we’ve been doing this for decades and haven’t found anything.”
A specific issue that dark matter detectors – like the Stawell Underground Physics Laboratory currently being built – are about to face, is that they’re just too good.
Right now, there are all sorts of particles hitting or passing through you. Everything from neutrinos (aka ghost particles) to muons are moving through you without you noticing.
A dark matter detector is placed deep underground and covered with thick shielding to stop the vast majority of particles from making it to the detector. Those that are left are supposed to be dark matter.
“Dark matter detectors are basically trying to filter out all that noise, to get the really rare, once-per-year events from a dark matter particle coming in and hitting the detector,” said O’Hare.
“They’ve pushed down the sensitivity of the experiment so precisely, that they’re now actually becoming neutrino detectors.
“And the problem is neutrinos are indistinguishable from dark matter.”
So how do you tell if you’ve found the elusive matter that makes up most of the Universe for the first time, or how do you tell if it’s just a neutrino?
The conference – called the CYGNUS Workshop on Directional Recoil Detection – will hopefully provide some answers.
The solution could be understanding where the particles came from.
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“Neutrinos, almost all of them, come from the Sun. And we know where the sun is, we know exactly where the Sun is,” said O’Hare.
“Dark matter, on the other hand, comes from the Galaxy surrounding us. So it will not align with the sun. Directional detection is not just measuring which atoms are getting nudged, but measuring which direction they’re getting nudged into.”
Of course, this is easier said than done, and the team organising the CYGNUS workshop are hoping that bringing together these researchers might forge a path forward.
“Telling the direction of a single atom which is nudged inside a detector … that’s very experimentally challenging,” said O’Hare.
“We’ve got lots of individual groups working on very, challenging, technological problems associated with extracting that information. And we’re coming together and hoping that with all of our combined forces, we can figure out what is the feasible way of actually doing this on a large scale.”
The CYGNUS Workshop on Directional Recoil Detection will take place from the 11th – 15th December at the University of Sydney.