sPHENIX EMCal discussion

[Martin Purschke <purschke AT bnl.gov>]

Dear Emcal (and HCal) aficionados,

a while ago we had a discussion how to go about getting better pointing
power for the beam position on the detectors. This spring we had been
reading the wire chambers for a general beam spot position, but had been
unable to read them event by event together with our DAQ because our
busy-vetoed trigger was way too late.

I have been back and forth with Sten, the engineer who makes the
firmware for the wirechamber controllers. He will make changes to the
controller firmware to be able to stack more events and accommodate
twice the current maximum delay. I had measured a delay of about 1.2
microseconds between the trigger that Ewa sends to the chambers, and our
trigger signal. We looked at the current setup parameters, and found
that we'd be ok with about 980 ns but not 1200.

The change that Sten will implement for us will get us well into the
range we need. That does not pre-empt other choices we had been kicking
around, but at least it is a viable option to get a 4-point beam vector
event by event.

Best,
        Martin


-- 
Martin L. Purschke, Ph.D.        ;   purschke AT bnl.gov
                                 ;   http://www.phenix.bnl.gov/~purschke
                                 ;
Brookhaven National Laboratory   ;   phone: +1-631-344-5244
Physics Department Bldg 510 C    ;   fax:   +1-631-344-3253
Upton, NY 11973-5000             ;   skype: mpurschke
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