Exploring the Hadronic Axion Window via Delayed Neutralino Decay to Axinos at the LHC

Abstract

The addition of the QCD axion to the Minimal Supersymmetric Standard Model (MSSM) not only solves the strong CP problem but also modifies the dark sector with new dark matter candidates. While SUSY axion phenomenology is usually restricted to searches for the axion itself or searches for the ordinary SUSY particles, this work focuses on scenarios where the axion's superpartner, the axino, may be detectable at the Large Hadron Collider (LHC) in the decays of neutralinos displaced from the primary vertex. In particular, we focus on the KSVZ axino within the hadronic axion window. The decay length of neutralinos in this scenario easily fits the ATLAS detector for SUSY spectra expected to be testable at the 14 TeV LHC. We compare this signature of displaced decays to axinos to other well motivated scenarios containing a long lived neutralino which decays inside the detector. These alternative scenarios can in some cases very closely mimic the expected axino signature, and the degree to which they are distinguishable is discussed. We also briefly comment on the cosmological viability of such a scenario.