I was thinking primarily of the hardware trigger, making sure we
were not throwing out any events, or spending too much time on events we
know are garbage. From what Baris just told me, LC0 is efficient, and the
LCer0 ADC spectrum looks like the others; we DO in fact see the real events
in LCer0. But there is also a lot of noise that fires the LCer0 TDC.
If I understand Eugene correctly, in the (e,e'n) analysis, for a
neutron on the right you cut on whether a Left Cerenkov TDC fired, in order
to get clean events. If LCer0 were quiet, you would not even have to worry
about whether the left Cerenkov that fired was related to the TOF that
fired. To clean up all the data we've taken so far, if the left Cerenkov
is #0, you have to also ask if the TOF number is 0 to 4 (or maybe 5?) to
allow for edge effects.
Is my understanding correct? If so, then we just have to weigh
the work and risks of changing the tube against the gain in (e,e'n) analysis.
Karen
At 10:23 AM 6/14/2004 -0700, Eugene J. Geis wrote:
>I believe there is a need to either disconnect it or replace it since
>statistics are rather limited on e'n events and (TOF plus CC in trig==2) is
>yielding a high number of events that shouldn't be in the trigger. The
>tube is
>bad, meaning very very noisy. In contrast to the signal on the scope from
>the
>other tubes, that PMT was not registering anything coherent, there was no
>trigger signal. And that tube was registering a hit in 3.2% of good ep
>events
>with electron Right, while R0 was registering a hit in 0.28% of electron Left
>ep events. The noise is completely random and happening a factor of ten
>times
>more than random signals in any other box. I know from neutron analysis that
>the CC cut is highly efficient in removing unwanted junk, and it could be
>more
>efficient. I think it is worth it.
>
>eugene
>
>Quoting Karen Dow <kdow@mit.edu>:
>
> >
> > 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
> >
> >
>
>
>
>--------------------------------------------------------------------------
>Eugene Geis
>PhD Student, Physics Department, ASU
>Research Affiliate, MIT-Bates Laboratory of Nuclear Science
>eugene.geis@asu.edu
>--------------------------------------------------------------------------
>-------------------------------water is good------------------------------
>--------------------------------------------------------------------------
> ** Check Out the Phatty Acidz @ http://www.phattyacidz.com **
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