Robert Michaels, email@example.com, Jefferson
Lab Hall A, Jan 2004
This all pretty old information, but I leave it here for anyone wanting to remember it.
Overview of trigger: Scintillators make the main trigger in each spectrometer arm. For coincidence experiments a coincidence is formed between the spectrometer arms. The main trigger is formed by requiring that scintillator planes S1 and S2 both fired (and both phototubes of the paddles that got a hit) in a simple overlap. To repeat, the trigger requires that one paddle in S1 and one in S2 both got a hit in both of their PMTs (4 PMTs total). The coincidence between spectrometers is formed in an overlap AND circuit. The Right Spectrometer singles triggers are called T1, the Left Spectrometer triggers are called T3, and the coincidence triggers are T5. Other triggers might be formed which require other detectors to measure the efficiency of the main trigger. The most important is T2 on R-arm and T4 on L-arm, whose definition has changed over time but typically require 2 out of 3 from among the S1, S2, and a 3rd detector like S0 or Cerenkov. During e94107 we form a new trigger from the aerogel, see trigger_coinc.html (the link shown above) for details.
The Hall A HRS trigger system is remotely configured by CAMAC modules. The main change that can occur during an experiment is in the delays required to adjust the timings of triggers which change with momentum and particle ID relevant for coincidence setup only. For single arm running, or high momentum (2 GeV), one may just use the defaults, but it may still be a wise investment in 2 minutes time to download in order to make sure of the state of the modules. If the power is turned off, the CAMAC modules certainly must be reprogrammed. Here are instructions to download the trigger
See also the Hall A DAQ/Trigger link page: hallaweb.jlab.org/equipment/daq/daq_trig.html.
R. Michaels -- e-mail: firstname.lastname@example.org