First results on the scalar WIMP-pion coupling, using the XENON1T experiment

We present firstresults on the scalar WIMP- pioncoupling from 1 t$\times$yr of exposure with the XENON1T experiment. This interaction is generated when the WIMPcouples to a virtual pionexchanged between the nucleonsin a nucleus. In contrast to most non-relativistic operators, these pion-exchange currents can be coherently enhanced by the total number of nucleons, and therefore may dominate in scenarios where spin-independent WIMP- nucleoninteractions are suppressed. Moreover, for natural values of the couplings, they dominate over the spin-dependent channel due to their coherence in the nucleus. Using the signal model of this new WIMP- pionchannel, no significant excess is found, leading to an upper limit cross section of $6.4\times10^{-46}$ cm$^2$ (90 % confidence level) at 30 GeV/c$^2$ WIMPmass.