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Dear Marco,<br>
Indeed all the questions are valid and necessary to understand in
order to make a definite statement. We are working with Pavel to
provide some information about his model and its
motivations/assumptions.<br>
<br>
To answer your questions about geographical dependence of SPE
spectrum, we are going to apply small collimator to bring our beam
spot size to smaller value in order to scan it more thoroughly, w/o
overlapping.<br>
<b><br>
Regarding independence of H12700 on HV:</b> I am glad you pointed
it out. I didn't pay enough attention to this particular point,
since gains themselves do not provide any criteria for MAPMTs
comparison. The quantum efficiency doesn't depend on HV, and
collection efficiency was smaller at any HV. It increased for H8500
at 1075V, but so should for H12700. You are right, the gains should
increase as well. There are might be some problems with our HV
setup, since slow control in CLAS was under some upgrade.
Fortunately, it doesn't change final answer. 1000V is correct for
sure, and collection efficiency is still smaller for H12700. Now if
1075V is in fact 1000V (HV slow control didn't work), it would bring
collection efficiency for H12700 higher at 1075V. But I can't see
any reason for it to be bigger than H8500 at 1075V. I will recheck
this point though (thank you).<br>
<br>
With that being said, it is extremely important that extraction of
this efficiency relies heavily on the model framework. It leads to
the your next question: the visible peak is indeed under the
pedestal. These are the events, where photoelectrons were produced
but weren't multiplied at all on first dynode due to the inefficiecy
of electron multiplying system. And these events do heavily
contribute to collection efficiency. <b>How Pavel's model determine
how big is this peak?</b> From my understanding the main criteria
is parameter myu - since it defines the relative number of 1PE
events, 2PE events,... to the pedestal events. We could in fact
remove this peak from 1PE, and include them into pedestal area,
however, it would have a negative impact on 2PE, 3PE peaks, which
would lead to the disagreement with data at higher amplitudes.<br>
<br>
Also, just an assumption: As you can see from 1PE spectrum on page
11 that H12700 events do not have apparent peak under pedestal, I
believe that it might be an effect of Hamamatsu trying to optimize
their dynode structure. Could it be that they succeeded to remove
the areas where photoelectrons are not multiplied, but... these
engineering solutions created large area on first dynode where
electrons multiply with worse secondary emission ratio? Combine it
with lower number of dynodes and we have smaller resultant
collection efficiency. Meanwhile H8500 has areas of dynode without
multiplication (peak under pedestal) and with "optimal"
multiplication.<br>
<b>These are clearly guesses,</b> that I am not sure we would be
able to test, but it provides very brief insight how Pavel's model
describes structures in H12700 spectrum.<br>
<br>
In conclusion, I will add more slides with these corrections.
Presentation will definitely be more complete with them.<br>
Thank you,<br>
Andrey.<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 08/20/2014 06:11 AM, Marco
Contalbrigo wrote:<br>
</div>
<blockquote cite="mid:alpine.LRH.2.03.1408201132470.3901@fe.infn.it"
type="cite">Dear Andrey, <br>
thank you for this nice and interesting piece of work.<br>
We may discuss it this Friday at the RICH meeting, anyway
<br>
I anticipate few comments.
<br>
<br>
If this report is intended (also) for Hamamatsu I guess
<br>
we should pay attention on completeness of information
<br>
and motivation of the assumptions (model). This is
<br>
important since your conclusions are somewhat in
<br>
contradiction with Hamamatsu claim the new dynode
<br>
structure is optimized for SPE.
<br>
<br>
In this sense, I would say the report needs at
<br>
minimum:
<br>
- page number
<br>
- a slide with the fitting formula/procedure
<br>
- an explanation/motivation of Pavel's model
<br>
<br>
but I think it calls also for - a reference SPE analysis where
only the center of
<br>
the pixel is illuminated or a SPE analysis as a
<br>
function of the laser spot within the pixel
<br>
- a cross-talk analysis
<br>
<br>
Indeed your conclusions heavily depends on the
<br>
funny shape of the H12700 SPE signal. Thus one
<br>
immediate question is how much this shape
<br>
changes within the pixel and/or if it is
<br>
affected by the cross-talk.
<br>
<br>
I find odd that the H12700 gain is independent of HV
<br>
(pag.8). Do you have an explanation for this ?
<br>
<br>
On page 11, where the SPE signal is shown,
<br>
are the dotted vertical lines the 5sigma cut ?
<br>
How can be fit a (small, but evident for H8500) SPE
<br>
peak under the pedestal ?
<br>
<br>
Thnaks again, Marco.
<br>
<br>
On Tue, 19 Aug 2014, Andrey Kim wrote:
<br>
<br>
<blockquote type="cite">Dear collaborators,
<br>
Please find H12700-H8500 comparison review attached.
<br>
"Short" summary: H12700 is still better than H8500 due to the
higher photocathode
<br>
quantum efficiency. The nearly uniform illumination of pixel
shows that SPE
<br>
spectrum is not as good as it was anticipated. It has more
complicated structure
<br>
than H8500. The structure was described using Pavel
Degtiarenko's model, and using
<br>
his model's fit results the collection efficiency was estimated
for both MAPMT
<br>
types. The H8500 demonstrated higher collection efficiency than
H12700 (unexpected
<br>
and rather saddening behaviour). Fortunately, H12700 has higher
photocathode
<br>
quantum efficiency, and it was determinative factor in H12700
superiority.
<br>
Please note that separation of quantum and collection
efficiencies is possible
<br>
within model framework only. However, the global efficiency
(decisive criteria) is
<br>
model independent as it is the fraction of events with signal
over pedestal's 5
<br>
sigma (assuming, of course, that light source is stable and
constant).
<br>
Any comments, suggestions or corrections are welcome!
<br>
Thank you!
<br>
<br>
<br>
</blockquote>
</blockquote>
<br>
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