Performance of the Endcap Time-of-Flight detector in the STAR beam-energy scan

TL;DR

The paper reports on the installation, calibration, and performance of the endcap time-of-flight detector at STAR, which enabled particle identification at new energy ranges during the beam energy scan.

Contribution

It presents the design, implementation, and performance results of the eTOF detector system at STAR for the BES II program.

Findings

Achieved a time resolution of about 70 ps.

Attained a particle identification efficiency of about 70%.

Enabled particle identification at center-of-mass energies from 3.0 to 7.7 GeV.

Abstract

The STAR experiment at RHIC at Brookhaven National Laboratory completed the installation of an endcap time-of-flight subsystem (eTOF) in February 2019. The eTOF subsystem provided essential mid-rapidity particle identification (PID) for the fixed-target (FXT) portion of phase II of the beam energy scan (BES II). The FXT program allowed BES II to include center-of-mass energies from $\sqrt{s_{_{NN}}} = 3.0$ GeV to $\sqrt{s_{_{NN}}} = 7.7$ GeV, not accessible by colliding beams. The eTOF detectors and readout electronics were designed for the CBM experiment at FAIR and adapted for use at STAR. In this paper, we describe the details of the system in terms of geometrical layout, acceptance, calibration, hit reconstruction, and particle identification. The system achieved a time resolution of about 70 ps and a PID efficiency of about 70\%, meeting the design goals of the project.