“Experts largely agree that a major portion of the mass in the universe consists of ‘dark matter’. Its nature remains completely obscure. One kind of hypothetical elementary particle that might make up the dark matter is the so-called axion. If axions with the right properties exist it would be possible to detect their presence through this entirely novel analysis of our data.”
Axions are important because finding them, if they exist, could hold the key to why the universe has lots of matter but relatively little antimatter.
Equal amounts of matter and antimatter would have been created when the universe began, and it should all have mutually annihilated, but the Universe clearly now has plenty of matter – but essentially no antimatter – left over; we do not understand why.
The data were collected for another purpose – to look at why the universe is dominated by matter and not antimatter – when it was realised that the measurements could be used to search for the presence of axions too.
“These results open a new front in the hunt for dark matter. They disprove the existence of axions with a wide range of masses and therefore help to limit the variety of particles which could be candidates for dark matter. And it’s fantastic to see that these results – which were being collected for another purpose entirely – could be used as a piggyback to search for axions too.”
“In our original experiment we took a single measurement and repeated it many times to determine the average value over a long time. When we’re searching for axions, we watch for whether the measurement fluctuates over time with a constant frequency. If so, it would be proof that there had been some interaction between the neutron and the axion. We never saw that.”
The paper, “Search for Axionlike Dark Matter through Nuclear Spin Precession in Electric and Magnetic Fields,” is published in Physical Review X. Explore further: Searching for axion dark matter with a new detection device.