G0 electronics and data acquisition (forward-angle measurements)

The G0 parity-violation experiment at Jefferson Lab (Newport News, VA) is designed to determine the contribution of strange/anti-strange quark pairs to the intrinsic properties of the proton. In the forward-angle part of the experiment, the asymmetry in the cross-section was measured for e⇒p elastic scattering by counting the recoil protons corresponding to the two beam-helicity states. Due to the high accuracy required to measure the few-part-per-million asymmetry, the G0 experiment was based on a custom experimental setup with its own associated electronics and data acquisition (DAQ) system. Highly specialized time-encoding electronics provided time-of-flight spectra for each detector for each helicity state. More conventional electronics, processing only a small fraction of the events, was used for monitoring (mainly FastBus). The time-encoding electronics and the DAQ system have been designed to handle events from the 128 detector pairs at a mean rate of 2 MHz per detector pair with low deadtime and with minimal helicity-correlated systematic errors. In this paper, we outline the general architecture and the main features of the electronics and the DAQ system dedicated to G0 forward-angle measurements.