First tracking performance results from the ATLAS Fast TracKer

Particle physicists at the Large Hadron Collider (LHC) investigate the properties of matter at length scales one million times smaller than the atom by colliding together bunches of high-energy protons and observing the decay products of the collisions. ATLAS is one of two general-purpose detectors that reconstruct the interactions and as part of a wide range of physics goals measures production of Higgs bosons and searches for exotic new phenomena including supersymmetry, extra dimensions of spacetime, and dark matter. Selecting the interesting collision events using hardware- and software-based triggers is a major challenge that will become more difficult as the LHC luminosity increases in future data. The ATLAS Fast TracKer (FTK) is a custom electronics system that performs fast hardware-based tracking of charged particles for use in trigger decisions. In 2018, two FTK ”Slices” covering portions of the ATLAS detector were installed and commissioned using proton-proton collisions, to prepare for physics data-taking in Run 3. The FTK track-finding and track-fitting strategies and the tracking performance for the FTK Slices are presented. Strategies for coping with changing beamspot and other conditions in future data are discussed. A strategy for triggering on displaced tracks from long-lived particles is presented.