Array of scintillator counters for PHOBOS at RHIC

An array of scintillator counters (“paddle counters”) for the measurement of number and energy of charged particles in heavy-ion gold–gold collisions for the PHOBOS experiment at RHIC is described. These simple, versatile, and highly efficient detectors provide a low bias and an easily understood level zero trigger. The paddle counters can also be used to select and measure event centrality. The information from the paddle counters used for triggering and event selection included the total signal height (proportional to the number of particles), the timing information of the hits, and the number of scintillators fired. The general characteristics of the paddle counters, their design parameters, and performance during the first run at RHIC are presented in this paper.