The ATLAS TRT Fast-OR Trigger for Heavy Ions in the LHC

The ATLAS heavy ion group has made important observations lately including light-by-light scattering and tau lepton pair production in Pb ion runs at the LHC. These analyses are part of the ultra-peripheral physics program, which studies events in which the electromagnetic clouds around the ions interact rather than the Pb ions themselves, giving photon-photon interactions at high energy. In order to further this program of study, higher statistics at low lepton transverse momentum (pT) is needed, but no suitable trigger exists in the ATLAS detector to capture such events. In order to provide such a trigger, the ATLAS Transition Radiation Tracker cosmics trigger known as the FastOR is being adapted for use in Pb-Pb collisions. The Endcap FastOR commissioning procedure and tuning of parameters for the heavy ion physics program are presented, as well as preliminary performance results from the September-October 2023 run.