The QCD axion provides an elegant solution to the strong CP problem. While the minimal realization is vulnerable to the so-called "axion quality problem,"we will consider a more robust realization in the presence of a mirror sector related to the standard model by a (softly broken) Z2 symmetry. We point out that the resulting "heavy"axion, while satisfying all theoretical and observational constraints, has a large and uncharted parameter space, which allows it to be probed at the LHC as a long-lived particle (LLP). The small defining axionic coupling to gluons results in a challenging hadronic decay signal which we argue can be distinguished against the background in such a long-lived regime, and yet, the same coupling allows for sufficient production at the hadron colliders thanks to the large gluon-parton luminosity. Our study opens up a new window towards accelerator observable axions and, more generally, singly produced LLPs.
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We would like to thank Matthew Daniel Citron, Jared Evans, Yuri Gershtein, Simon Knapen, and Diego Redigolo for very useful comments on the draft. We would also like to thank Prateek Agrawal, Evan Berkowitz, Zohreh Davoudi, and Simone Pagan Griso for helpful discussions. This research was supported in part by the NSF Grants No. PHY-1620074, No. PHY-1914480, and No. PHY-1914731, and by the Maryland Center for Fundamental Physics (MCFP). A. H., Z. L., and R. S. acknowledge the hospitality of the Kavli Institute for Theoretical Physics, UC Santa Barbara, during the “Origin of the Vacuum Energy and Electroweak Scales” workshop, and the support by the NSF Grant No. PHY-174958. A. H. and Z. L. would also like to thank Pittsburgh Particle Physics Astrophysics and Cosmology Center (PITT-PACC), The Munich Institute for Astro- and Particle Physics (MIAPP), and Aspen Center for Physics (supported by NSF Grant No. PHY-1607611) for support from their programs and providing the environment for collaboration during various stages of this work.
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