Axion-like particles (ALPs), relatively light (pseudo-)scalars coupled to two gauge bosons, are a common feature of many extensions of the Standard Model. Up to now there has been a gap in the sensitivity to such particles in the MeV to 10 GeV range. In this note we show that LEP data on Z→γγ decays provides significant constraints in this range (and indeed up to the Z-mass). We also discuss the sensitivities of LHC and future colliders. Particularly the LHC shows promising sensitivity in searching for a pseudo-scalar with 4≲ma≲60 GeV in the channel pp→3γ with m3γ≈mZ.
Jaeckel, J., & Spannowsky, M. (2016). Probing MeV to 90 GeV axion-like particles with LEP and LHC. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 753, 482–487. https://doi.org/10.1016/j.physletb.2015.12.037