Triggers are
generated by the PMT signals from the scintillator planes and from
calorimeter blocks were sent to DAQ. To make sure that only good events
coming from the target are used for the analysis, each event is
assigned a variable event type based on the signals from scintillator
planes for this event. The trigger signals are sent to the Trigger
Supervisor (TS) module which starts the DAQ readout. Most inputs of the
TS can be individually prescaled. Triggers, which are accepted by the
DAQ, are then re-timed with the scintillators to make gates for the
ADCs and TDCs. The re-timing removes trigger time jitter and makes the
timing independent of the trigger type. Events with event type equal to
1, 2, 3, 4, 5, 6, 7, 8 are called T1, T2, T3, T4, T5, T6, T7, T8
events, respectively.
The variable event type is assigned to each event as follows:
Trigger 1
-
T1 is a Photon Arm singles trigger. It is
formed in the following way:
- The analog signals from every 2 x 4 array of lead glass
blocks, except the outermost layer of blocks, are first summed by a
custom-made linear-summing module. Four of the summed signals from the
2 x 4 array are summed again to form a signal summed over 32 blocks.
Each of the sum32 signals are sent to discriminators to form logical
signals.
- Total 56 signals from the discriminators were combined
in a master OR, the output of which gives the Photon Arm trigger T1, if
the energy deposited in one of 32 group blocks of the calorimeter is
above the effective threshold value set in the discriminators by
programmable DAC.
Trigger 2
- T2 is a Photon Arm cosmic trigger:
- It was organized by using two plastic scintillator paddles, which were placed at the top
and the bottom of the calorimeter.
- The trigger signal is formed as a coincidence of signals of the top and the bottom paddles.
Trigger 3
- T3 is a main Hadron-arm trigger.
- Logical AND of the left and the right PMT signals forms a signal from a paddle.
- Logical OR of six paddles in each scintilator plane forms a signal from S1 and S2.
- Logical AND of S1 and S2 forms forms the trigger signal from Hadron-arm.
Trigger 4
- T4 is an additional Hadron-arm trigger.
- It is based on logical OR of three coincidence S1&S2,S1&S0 and S2&S0.
- This is a redundant trigger used for trigger efficiency measurement.
Trigger 5
- T5 is a coincidence of signals, individually use to form T1 an T7. The width
of the photon trigger pulse is set to 10 ns,
so that the coincidence events are synchronized with the photon trigger.
Trigger 6
Trigger 7
- T7 is a trigger from S0 scintillator counter signal. The logical signal from bottom PMT
of the S0 paddle forms the Left-arm trigger.
- The logical AND of the signals from up and bottom PMTs of the S0 paddle is used for Hadron-arm re-timing.
- The coincidence window is determined by the width of the hadron trigger pulse and is set to 100 ns.
Trigger 8
- T8 is a 1024 Hz pulser trigger. A 1024 Hz pulser is fed to Trigger Supervisor. It is used to measure
the dead time of the electronics.
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