Because dark and ordinary matter interact rarely, these searches are challenging. To date, the XENON1T experiment holds the best limits by having scanned over a ton of liquid xenon for almost a year.

In our work, we have searched for the interaction of dark matter particles with pions in atomic nuclei, manifested as characteristic xenon nuclear recoils in the XENON1T data. Our analysis finds no evidence for a dark matter-pion interaction, but nonetheless sets the first limit on its strength.  Previous analyses only considered the interaction of dark matter with protons and neutrons (nucleons).

However, nuclei are more than collections of nucleons. In fact, nucleons interact due to the strong nuclear force, which arises for example from the exchange of virtual pions. Interestingly, dark matter could scatter off these pions, an interaction we have constrained for the first time. The limit set by our analysis has to be obeyed by all theoretical models of dark matter.

The article is published:
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.071301