History: D.ctimeL1A

To link together the "times" measured with the Neutron Detector Electronics (relative to the L1A) and those measured with the BigBite electronics (relative to the BBtrig), it helps to understand the way the two trigger systems worked.

The ((Neutron Detector)) generated triggers using an energy sum over multiple modules; this trigger is designated as __T1__. The BigBite spectrometer generated its own trigger signal, called __T2__, from a threshold placed upon the energy deposited in its calorimeter. The T1 and T2 signals were then passed to a coincidence unit, such that a logical __AND__ of the signals formed the coincidence trigger __T3__. The leading edge of T3 was determined by when the overlap of T1 and T2 occurred. The trigger supervisor would then form the L1A with a time relative to the accepted trigger. The ASCII figure below tries to demonstrate this for a normal "good" T3 event.

~pp~
T1 ___________ _________________
| |
|________|

T2 ______ _________
| |
|_____________________|

T3 __________ ______________
| |
|___________|

L1A __________
|
|__________________________
~/pp~

Prior to the experiment, the relative timing of the T1 and T2 trigger signals into the discriminator were set such that T1 should come after T2, and so determine the time of the T3 and the L1A. The width of the T1 and T2 signals measured before the experiment to be ~50ns and 100ns, respectively.