We will be resuming trigger studies tomorrow morning. For the
next couple of weeks (including beginning WC work) the Compton
polarimeter will run tests on the 0-8 shift. Trigger and WC
work will occupy the 8-16 and 16-24 shifts.
Regarding the data set, we have lots of data with gas. I would
like to accumulate about 2 hours of data with gas OFF to look
at backgrounds in the data set.
For the trigger, there are (at least) 4 major problems to solve.
(1) There continues to be miscabling and perhaps mismapping of
ADCs and TDCs (see BlastTalk from Genya).
(2) There still exists an unexplained 15 ns between the left and
right OR of meantimes relative to the start counter.
(3) We see e-p coincidences with e left and p right but not vice
versa (sorry, I don't have an italic font on PINE).
(4) We still have problems with the TDC spectrum for RTOF11 top
and LTOF12 bottom.
So the tasks this weekend are aimed at understanding and fixing
these problems. Regarding (1), Genya made some suggestions. As
he pointed out, if both top and bottom are miscabled, the result
is still ambiguous. I have a more time consuming but foolproof
method. Using the present trigger, and the capability to mask off
arbitrary discriminator channels, start by masking off all but
one left sector TOF, both top and bottom, except for LTOF15 which
is the start counter. In a very short run, a couple of minutes, you
should see data in the ADCs and TDCs for the left top and bottom
corresponding to only that TOF (and LTOF15, of course). Make sure
they are the correct locations. Then mask that TOF off and unmask
the next one. Do for all left TOFs. Then unmask all LTOFs and mask
all RTOFs but one and repeat the prcedure. I would estimate that
you should be able to do 3 or 4 of these short runs per fill. So
to do all TOFs should take roughly 10 fills. This problem has been
plaguing us for too long now. It is time to put it to rest.
Regarding (2) and (4), these will have to be looked at with beam
off, using the flasher. With the flasher on, pull the left sector
input to the retiming OR and look at the retiming OR output at the
TDC (after the delay) on the scope while triggering the scope with
the start counter TDC input (LTOF15). Then plug the left sector
back in and unplug the right sector from the OR. The time will
either shift or not. By how much and why?
Regarding (3), there is a suspicion that this is due to the
meantimer restricting the width of the output logic signal from
the 4516 AND unit to the delay and MLU. One test that can be done
is to change the logical programming of the 4516 from AND-AND to
either AND-OR or OR-AND to take the meantimer out of the required
coincidence. To figure out which one is correct, one has to (a) loof
and see which inputs into the 4516 are being used by top, bottom,
and meantimer (i.e. A, B, or C inputs) and then (b) check the manual of
the 4516 to see if AND-OR means A AND B OR C (which is what I think I
remember) and OR-AND means A OR B AND C. Putting the meantimer
in OR mode will allow the 100+ ns widths of the top and bottom
CFDs to propogate through. Take a long enough run (2 hours) to
get coincidences. Note that the TDC spectra will be shifted by
about 30 ns (the intrinsic delay in the meantimer) and spread out
by +/- 7 ns which is the spread of events near the top or bottom
relative to the middle. So the analysis will be more complicated.
But we hope to see equal numbers of coincidences from both sides.
Unfortunately, I could not find a 4516 manual in the counting room.
We should have 3 of them. If anyone has one, please return it to
the counting room.
The solution to problem (3) is to put a leading edge discriminator
immediately following the 4516 in order to reset the width to
100 ns. Tavi has said he will do this either Saturday evening or
Sunday evening depending on where we are in the plan.
The order of tasks is that the NO GAS runs should be done first
before changes may be made, so that we can compare to the body
of data that we have. After that, the order of the other tasks
is arbitrary and depends upon the expertise and confidence of the
shift crew at that time.
-- John R. Calarco Dept. of Physics Univ. of New Hampshire Durham, NH 03824 phone: (603)862-2088 FAX: (603)862-2998 email: calarco@unh.edu
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