Mass or interaction, but not both

If upcoming direct searches discover the elusive dark matter in the universe, they may be able to measure the mass of the particle or the way it interacts with ordinary matter, but can only do both if we’re lucky, researchers from the UvA Institute of Physics argue.

It is one of the great open questions of modern-day physics and astronomy: what is the mysterious dark matter in the universe? Astronomers suspect that the universe contains much more matter than they can see through there telescopes – simply because there is much more gravity than visible matter can account for. So far, however, nobody has been able to find particles that this dark matter can be made of.

Rare interactions

Yet, many astronomers and particle physicists are optimistic that a dark matter candidate particle can be found soon, in the next generation of experiments and observations. While this may be true, Amsterdam researchers now point out that even if such a new dark matter particle is found, this does not automatically mean that we will immediately know all of its properties.

In their investigation, the researchers looked at planned underground detectors which aim to detect dark matter by looking for its rare interactions with ordinary atomic nuclei. The as yet undiscovered dark matter particle has an unknown mass (how heavy it is) and an unknown cross section (how strongly it interacts with nuclei).

Using new statistical tools, inspired by a concept known as ‘information geometry’ that the same researchers developed earlier this year, the physicists mapped out what a discovery would look like, without assuming a particular dark matter particle mass or cross section – allowing to explore a wide range of these dark matter properties.

New materials and techniques

It was found that a discovery using multiple different target materials that the dark matter particle can interact with, will substantially improve the measurement of the dark matter properties. However, even with multiple detectors, it will be hard to measure the mass of heavy dark matter particles and at the same time understand their precise interactions. Only over a narrow range of properties can both of these things be measured simultaneously.

This result, which was accepted for publication in Physical Review Letters last week, should spur the dark matter community to explore new detector materials and techniques which will improve the prospects for pinning down the properties of the dark matter particle in the event of a future discovery.

Reference

Assessing near-future direct dark matter searches with benchmark-free forecasting, Thomas D. P. Edwards, Bradley J. Kavanagh, and Christoph Weniger, Physical Review Letters 2018. (arXiv preprint