-=The features of D.ctimeL1A[[0]=-
- The ((NeutronDetector)) 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 (see ((GenDocTrig))), 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.
+ The ((NeutronDetector)) 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 (see ((GenDocTrigger))), 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.
::__A. Normal "good" event where T3 determined by T1 time, and L1A by T3__::~pp~
where T3 and the L1A are timed exactly relative to T2.
- To regenerate the reference signal (which we call BBtrig) for the BigBite arm, the L1A was retimed with respect to a copy of the T2 signal by sending them to a retiming module. If the T2 came very early, it is possible for its leading edge to become lost such that the retimed-signal was determined only by the time of the L1A. In this case, the diagram could look like this:
+ To generate BBtrig (noted in the trigger diagrams of ((GenDocTrigger)) as "L1A(retimed)"), the reference signal for the BigBite arm, a copy of T2 and the L1A are passed into a retiming module. The retiming module is supposed to generate a signal with a fixed-delay to T2, or if T2 is missing (normally the case for a T1 event) generate a signal with a fixed-delay with respect to the L1A. If the T2 came very early, it is possible for its leading edge to become lost such that BBtrig is aligned with the L1A; this can be checked by looking at the time distributions for detectors in BB (eg: -+B.s.time[[B.s.trpad[[0]+-) for this class of events. In this case, the trigger timing diagram could look like this:
::__C. Forced retiming case: timing of BBtrig determined by L1A, NOT by T2__::~pp~
- T2d __________________ _
+ T2d ___________ _
(delayed) | |
|________________|
- BBtrig ________________
(T2d & L1A) |
|___________________
+ BBtrig ____
|
|______________
+ ~/pp~
- |<- ->|r /> fixed delayr />r />~/pp~
+ All these effects together result in D.ctimeL1A and D.bit3 distributions that are shown in the following plot of D.ctimeL1A (y-axis) vs. D.bit3 (x-axis). Note that to get the correct "first" recorded T3 time from the 1877 TDC, you have to get the last readout value from the TDC so -+D.bit3[[Ndata.D.bit3-1]+- must be used.
- All these effects together result in D.ctimeL1A and D.bit3 distributions that look like in the following plot, where the top is D.ctimeL1A (y-axis) vs. D.bit3 (x-axis), and the two plots on the bottom show the top plot's projections onto the two axes and how the features show up.
+ {img src=show_image.php?name=L1A_to_T3_to_BBtrig.gif }
- {img src="img/wiki_up/D.ctimeL1A_features.gif" }
| ![[hide]](javascript:icntoggle('mod-mnu_application_menu','mo.png');)
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