Perfomance and Capabilities of the Endcap Time-of-Flight Detector in the STAR Beam Energy Scan

One of the main physics goals of the Beam Energy Scan (BES) program at RHIC is to study the QCD phase diagram, especially around the phase transition

between the quark-gluon plasma (QGP) and hadronic matter. BES Phase-I studied Au+Au collisions from center-of-mass energy ($\sqrt{s_{_{\rm{NN}}}} $) of 7.7 to 62.4 GeV. BES Phase-II extended these measurements with higher statistics, detector upgrades, and the addition of a fixed-target program that pushed the collision energy down to 3.0 GeV. The FXT program comes with its own challenges, namely with midrapidity moving outside of the acceptance of the barrel Time-of-Flight detector as the beam energy increases ($0 < \eta_{_{\rm{bTOF}}} < 1.50$ in FXT mode). To expand the available phase-space and recover midrapidity for the higher FXT energies, the endcap Time-of-Flight detector (eTOF) was implemented during BES-II in 2019. eTOF extends the pseudorapidity coverage by 0.7 units ($1.55 < \eta_{_{\rm{eTOF}}} < 2.17$) in FXT mode, and allows for midrapidity measurements for collision energies up to $\sqrt{s_{_{NN}}} = $ 7.7 GeV. This talk will outline the performance of eTOF during BES-II, which had a timing resolution of 70 ps. The talk will also discuss how eTOF is configured for different physics analyses, with particular emphasis on its role in the critical point search at STAR.