Di-track search for heavy, charged particles with high ionization energy loss with the ATLAS detector

In the search for Beyond-Standard-Model particles, long-lived particles (LLPs) offer an exciting sector yet to be fully explored. Some Supersymmetric models suggest massive, charged, long-lived particles, such as R-Hadrons and staus, may be produced at the Large Hadron Collider (LHC) in proton-proton collisions of sqrt(s) = 13 TeV. These LLPs would present as high-momentum tracks with high ionization energy relative to the minimum-ionizing SM particles of similar momenta, and are detectable using ATLAS's Pixel Detector to measure ionization energy loss. These massive particles do not have simple SM backgrounds which can be easily simulated, but rather can be mimicked by detector effects and mis-reconstructions. As such, a data-driven method is formed to estimate the background. A previous study for single-track events set strong limits on the possible masses for long-lived charginos and R-Hadrons. We present an extension to the previous analysis which requires two candidate tracks per event. The di-track selection has greater sensitivity for pair-produced staus with lifetimes of 10 ns or longer. This analysis utilizes the full ATLAS Run 2 dataset with integrated luminosity of 139 fb^-1.