Ultra long-lived particles searches with MATHUSLA

Many extensions of the Standard Model include particles that are neutral, weakly coupled, andlong-lived that can decay to hadronic and leptonic final states. The ATLAS, CMS, and LHCb experiments have performed searches at the LHC and significant exclusion limits have been set in recent years.In this talk, we describe the MATHUSLA surface detector (MAssive Timing Hodoscope for UltraStable neutraL pArticles), which can be implemented with existing technology in time for the turn-on of the high luminosity LHC (HL-LHC). We installed a small-scale test stand on the surface above ATLAS IP in autumn 2017 for timing measurements to study efficiency of downward cosmic track rejection. This will provide useful information for the design of the main detector and important inputs for the future physics and detector simulations.