We propose a new collider probe for axionlike particles (ALPs), and more generally for pseudo-Goldstone bosons: nonresonant searches that take advantage of the derivative nature of their interactions with Standard Model particles. ALPs can participate as off shell mediators in the $s$ channel of $2\to 2$ scattering processes at colliders like the LHC. We exemplify the power of this novel type of search by deriving new limits on ALP couplings to gauge bosons via the processes $pp\to ZZ$, $pp\to \gamma \gamma$, and $pp\to jj$ using run 2 CMS public data, probing previously unexplored areas of the ALP parameter space. In addition, we propose future nonresonant searches involving the ALP coupling to other electroweak bosons and/or the Higgs particle.

• Received 12 September 2019
• Revised 17 December 2019
• Accepted 6 January 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.051802

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Published by the American Physical Society