See at the bottom for the run plan
A more careful study shows that the collimator effectively reduces
background on "candidate" ep events (a candidate has +-l/r charges and two
vertex within 1 cm, and comes from the region z<20 cm) by a factor of
2.0-2.5, not 10 as reported. For this, you have to compare only to runs
2689 2692 2693, which by far had the best beam with reverse blast polarity
and before collimator.
For the en "candidates" (en trigger and one track on the left) there is
no reduction. In other words, the collimator helps only in cleaning up
events with two tracks. - PLEASE note elog entry 16651.
Indeed the rate went up x2-3, as noticed by many, and the deadtime becomes
40-50 %. Regarding the charging up of the wch: the bqms have clearly
improved another factor 2 with the collimator, bqm-left counts 15 Hz/mA
(that is ca. 1 KHz at 100 mA!!). Is this really bad???
With total CODA incoming trigger rates of 1 KHz we need the second level
trigger or we'll throw away 50 % of the good data. With a second level
trigger the total trigger rate will be again < 200 Hz (!!). See
count_2ndleveltrig.C
**** run plan
- continue d2 data taking until tomorrow morning. We should have > 400 C
by then (indeed we gather less now because of deadtimes)
- Analyze vertical scan data to determine best beam position. I believe we
already know for the horizonthal (h_bump = 0). Have ccr adjust the beam
position if necessary (vertical only). Take 400 C (gated) of empty
target data.
_ This should bring us to saturday evening. Switch to singles: coda
configuration "singles" , trigger singles_cc_only.settings. Take 400 C
of b-gated single arm data. Compare to h2 coinc data
_ Sunday morning/afternoon we should repeat measuraments at 30% field and
no field data with h2 target
- Beam time stops monday morning at 7 am.
--
________________________________________________________________________________
Tancredi Botto, phone: +1-617-253-9204 mobile: +1-978-490-4124
research scientist MIT/Bates, 21 Manning Av Middleton MA, 01949
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