Physicists looking for dark matter excited by finding nothing

Nearly 1.5km underground in the US state of South Dakota, scientists have narrowed the search for dark matter particles using the world’s most sensitive detector.

Astronomical observations suggest that gravity around galaxies only makes sense if there is more matter than the objects we can see. In fact, this elusive dark matter, should be 5 times more plentiful than ordinary visible matter.

But, because dark matter interacts weakly with ordinary matter except through its gravitational pull, finding and proving the existence of dark matter has remained out of reach.

One candidate for dark matter is a theoretical group of particles referred to as WIMPs, or weakly interacting massive particles.

Now a new record has been set for what not to look for in the search for dark matter particles.

The result was achieved at the US Department of Energy’s Lawrence Berkeley National Laboratory using the world’s most sensitive dark matter detector, LUX-ZEPLIN (LZ).

LZ scientists say in a media release that the detector allowed them to probe almost 5 times deeper than any other experiment in the search for dark matter. What they found is no evidence of WIMPs above a mass of 9 gigaelectronvolts/c² (GeV/c²). For comparison, the mass of a proton is slightly less than 1 GeV/c².

“While finding ‘nothing’ doesn’t sound like much of a result, this is hugely important in narrowing down where we could find direct evidence of dark matter,” says University of Sydney physicist Theresa Fruth who has worked on the LZ project for 9 years. “Will dark matter fit snugly into the Standard Model of particle physics, or will its discovery need us to rewrite our theoretical models? We simply don’t know yet.”

Fruth emphasises that understanding the nature of dark matter will help us understand the very nature of the universe.

“We wouldn’t exist without this mysterious yet fundamental piece of the universe; dark matter’s mass contributes to the gravitational attraction that helps galaxies form.”

“This detector is the best asset we have anywhere in the world in our hunt for WIMP dark matter over coming years,” Fruth says. “This result shows how sensitive the detector is and how useful it will be in helping us to solve this most intriguing of scientific puzzles.”