Second and third order fixes that will bring sentivity to 100% in
the dE/dx vs. beta area will be realized over the next 10 days
without any additional detector down time. They'll be introduced
on the next two maintenance days after all needed parts are received
at Gran Sasso and electronics set ups are finalized.
Data beyond RUN 14078 (03-JUN-1997) should represent homogeneous detector
running, sensitive to all physics analyses. More detailed updates will
be appearing on our MACRO Online page at
http://wsgs02.lngs.infn.it:8000/macro/mol.html
Finally, I would like to mention that all our technical personnel and our
physicist shift workers here (M. Orsini, S. Stalio, Ioannis K., P. Saggese,
G. Tarle and L. Gray) made an exceptional effort in getting the job done.
========================================================================
Dear MACRO people,
For those of you who heard the relevant talks in Ann Arbor or followed
the discussion that has been going on since several months now through
the Caltech mailing lists you know by now that this fix brings MACRO to almost
full sensitivity to all the dE/dx and beta range. The only enemy of the
hardware at this moment is the PMT afterpulsing which in some counters
may blind us on particles slower than ~5x10^-4c that will almost saturate
the PMTs.
The fix was realized in 8 days and included the high-charge calibration
of every single channel in MACRO. During these days, the only acquisition
"dead" time that the fix operation might have introduced comes from
the one associated with stopping and restarting MACRO a couple of times
more per day. Full MACRO acquisition was maintained in 2/3 of the detector
all the time.
A first pass on the real and calibration data indicates that the fix
is doing its job. We are currently working on going through all WFD
channels systematically and verifying that both the low and high
pulse response of the system is as expected.
The only *side effect* of the fix that was not appreciated to its full
depth at the beginning is a 10-15% increase in the overall datarate
and a slight rise of the acquisition dead time from 1.5% to 1.8%.
This was observed over the last 10 days but only recently Ioannis K. and
Chris Orth after going through the data and hardware realized its full
extend: the decrease of the coupling capacitor on the WFD discriminator
circuity creates deliberate sharping of the RC under/overshoots.
At the same time though, it creates enough overshoot for typical muon
pulses so that to start signal disitization.
This lasts of the order of ~3microsecs (i.e. 1200bytes) following every
typical muon during which practically pedestals are read. Given the number
of muons per run that we have, this results in extra ~40MB of WFD data
per 6 hours of running.
The items that are left in order to declare the operation complete are
listed below. We expect to get done with all of them within the next
10 days. *No* extra detector down time will be required. All of them will
be prepared in advance and inserted in the detector on the next two
maintenance days. Here's the list:
- commissioning of the new trigger (LaMosska) to save WFDs on PMT afterpulsing
- finalizing WFD readout protocol (Streamer Tube, TOHM activity, LaMosska)
Periodic calibrations will remain an on going project in order to make sure
the low and high charge response of the system remains as designed.
A full log of the fix operation follows for those of you who will be
looking at WFD data (and not only...) of this period. Needless to say,
let us know of any sort of problems you happen to find when looking
at the data. If you find everything fine, it would still be nice to
hear from you ...
Date First RUN After...
==========================================================================
02-MAY-1997 13912 SM3 PMT fanout and WFD modification
21-MAY-1997 14006 SM4 PMT fanout modification
27-MAY-1997 14039 SM4/5/6 WFD modification
28-MAY-1997 14046 SM5 PMT fanout modification
29-MAY-1997 14051 SM6/SOUTH PMT fanout modification
SM1/SOUTH/SM2 WFD modification
30-MAY-1997 14055 SM2&1/2 of SM1 PMT fanout modification
03-JUN-1997 14078 Last 1/2 of SM1 PMT fanout modification
06-JUN-1997 Last instalment of high-charge LED calibs
--Erik Katsavounidis