  The Cooling Storage Ring (CSR) External-target Experiment (CEE) at the Heavy
Ion Research Facility in Lanzhou (HIRFL), China, is the first multi-purpose
nuclear physics experimental device to operate in the Giga electron-volt (GeV)
energy range. The primary goals of the CEE are to study the bulk properties of
dense matter and to understand the quantum chromo-dynamic (QCD) phase diagram
by measuring the charged particles produced in heavy-ion collisions in the
target region with a large acceptance. The CEE is a spectrometer that focuses
on charged final-state particle measurements running on the HIRFL-CSR. The
time-of-flight (TOF) system is critical for identifying charged particles in
the GeV energy region. In the CEE spectrometer, the TOF system consists of
three parts: T0, internal TOF, and external TOF, which are used for the
final-state particle identification. The T0 detector provides a high-precision
start time for the TOF system by measuring the crossing time of the heavy ion
beam. This study details the design, performance simulation, and performance
testing of the T0 detector. The simulation results and heavy-ion beam test show
that the T0 detector prototype has an excellent time resolution, which is
better than 30 ps, and fulfills the requirements of the CEE.
