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User name R. Michaels
Log entry time 15:12:13 on July 08, 2010
Entry number 330820
This entry is a followup to: 330812
keyword=re: fEvtHdr.fEvtType vs D.evtypebits
Sorry, this little problem Ole re-discovered is a time bomb, but
not a real problem.
The trigger supervisor is programmed to give the "CODA event type".
It turns out that if a trigger N arrives early (and survives prescaling)
then the event type is N, but if any triggers arrive within 10 nsec --
which is likely since we aligned them -- the event type is somewhat
arbitrarily fEvtHdr.fEvtType == 5. Otherwise you'd need to program a
matrix for what all the overlap possibilities mean, which is experiment
specific and fraught with error. There is some history to this :
event 5 was, for years, the coincidence trigger and I figured this
choice reduced the chance of mistakes -- like ignoring them. Even if
you could argue we should fix the TS programming, it has a hardware
time window of 10 nsec which is arbitrary and again experiment-specific.
Solution: don't use fEvtHdr.fEvtType !
Instead, use D.evtypebits. It's a bit pattern formed from TDC inputs from the
trigger supervisor. The input to the TDC are the N triggers *after* prescaling.
There are also TDC inputs without prescaling, if you like.
This is also documented on my trigger web page.
1. Want trigger 4 and don't care if others co-exist
2. Want trigger 4 and demand that NO others co-exist (i.e. survive
3. Want trigger 6 and don't care if others co-exist
Now all this depends on some cuts on TDC (to define the bits) being
correct in THaNormAna, but I think Alexandre checked this for APEX.
It should be re-checked in post-run analysis.
A copy of this log entry has been emailed to: ole