Advancing the phenomenology of GeV-scale axion-like particles

Abstract

Searches for axion-like particles (ALPs) with masses in the GeV range are a central objective of present and future Intensity Frontier experiments. Interpreting these searches demands a reliable description of ALP production in hadronic collisions and decay. The prescription currently adopted by the community (i) depends on parameters of unphysical chiral rotation used to match gluonic ALP interactions with the interactions in terms of hadronic bound states, (ii) misdescribes the mass scaling of the ALP flux, and neglects mixing with heavy pseudoscalar resonances. We introduce a framework that treats GeV-scale ALP interactions in a chiral-rotation-invariant manner, includes their mixing with heavier excitations $\pi(1300)$, $\eta(1295)$, and $\eta(1440)$, and properly describes their production channels. When applying our description to proton beam experiments, we find that existing bounds and projected sensitivities shift by up to an order of magnitude relative to earlier estimates. We further delineate the dominant theoretical uncertainties, which originate from the still-incomplete experimental knowledge of the spectrum of pseudoscalar excitations.