I think this tube is bad in the sense that it is noisy, not in the
sense that it isn't working at all. So it's causing LCer0 to put a lot of
spurious hits into the trigger system, rather than reducing the number of
hits. LCer0 counts at 7-10 times the rate of the other left Cerenkovs in
the scalers.
Even though LCer0 is noisy, it doesn't appear to be giving us a
lot of extra singles events, or a lot of extra "2 TOF in one sector"
events, the only event types that require a Cerenkov. Looking with nsed,
less than 10% of those types of events come from an accidental between
LCer0 and a TOF that's not LT0-3. Presumably the second level trigger
cleans things up.
It's not clear to me that we NEED to change out the tube. There
is probably manpower available, and access to the pit. And I believe we
have spares. Chris Vidal will have to show a technician how to do it, as
the two guys who have done it recently have both been laid off. But if the
tube is working, just noisy, do we want to replace it (and have to
gain-match it, possibly have a different problem that DOES affect the data)?
Karen
At 10:46 AM 6/11/2004 -0700, Eugene J. Geis wrote:
>The bad tube in CC_L0 is the top center PMT tube... Do we have spare
>PMT's and
>do we think it's possible to have it replaced over our shutdown? I would
>volunteer to do the work but I'll be in Maine for the next two weeks.
>eugene
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