Hello,
Just to avoid the spreading of a rumor: it is true that we do
see spurious peaks in the TOF adc spectra. These move up and broaden
with the pmt HV. However, their "energy" and rate simply does not make
sense with "background from the room".
We know how to get a clean (at least 99.5% clean) cosmic spectrum and we
have no reasons to believe this will be a problem wht a L&R coinc trigger.
Since I was the first to put this hypothesis forward, I just want to
emphasize that that conclusion has lost quite some credibility. The
main fact is that this supposed background should be about 2 Mev! and 3
times more than cosmic. On other hand the rates seem to exclude that we
are triggering on noise, unless this is somehow correlated top and
bottom, or maybe its some tube feature we do not understand.
I think it's worthed to make it clearer.
Other than that, the good news is that we clearly see that TOF pedestals
per se are very stable (1-2%) over several days, their spread can be +- 20 %.
I want to dispute the binning used in fitting the ADC that seems to be quite
unreasonable and could lead to unstable results, particularly for low statistics.
This seems to have brought to a few bad spots here and there, but these are
details that we can fix "internally".
Regards,
-- tancredi
________________________________________________________________________________
Tancredi Botto, phone: +1-617-253-9204 mobile: +1-978-490-4124
research scientist MIT/Bates, 21 Manning Av Middleton MA, 01949
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
On Mon, 28 Oct 2002, Adrian T Sindile wrote:
> The small paddles have been removed, all TOFs recabled, Start Counter
> disconnected from the efficiency configuration.
> Everything in the D-tunnel is back (T-s used for small paddles removed).
> We took cosmic runs 2372 and 2374 to check if everything is back as it
> should be after one week of plugging and unplugging cables for efficiency
> measurements.
>
> In run 2372, Cerenkovs were in X-mode. That gave us the ugly spikes in
> ADCs again. I really wish I understood those (for now, we think it is
> background in the South Hall, I will look more into this when I get a
> chance).
>
> Run 2374 - Cerenkovs required, spikes gone (as expected).
> On the left sector four ADC channels looked different than the target (one
> was like that a week ago too, we checked). They need fine-tuning.
> On the right, two channels looked different, Tancredi knew about those
> (they were 50 Ohms terminated, thus only giving half the signal).
>
> Over all, it was worth doublechecking everything in our opinion.
>
> We never got to start Cerenkov testing with flasher, as we wanted
> initially - but it seems the priority is to finish checking the TOFs (that
> includes timing). The above TOF channels should be fine-tuned before
> retiming...
>
> Hauke and Adrian
>
> -------------------------------
> Adrian Sindile
> Research Assistant
> Nuclear Physics Group
> University of New Hampshire
> phone: (603)862-1691
> FAX: (603)862-2998
> email: asindile@alberti.unh.edu
> http://einstein.unh.edu/~adrian/
>
>
>
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