Impressions of the calorimeter review and your notes

[Alex Dzierba <dzierba@indiana.edu>]

Dear Elton et al

Before addressing your e-mail directly, I want to say that the
calorimeter review went very well.  I thought that the committee
members were great to work with, asked excellent questions and
clearly wanted to make the exercise a very constructive one - which
it was.  During the close-out they pointed out areas that need more
attention as well as pointing out areas of significant progress.
The post-close-out interaction with the committee was also
very useful.   Assembling the pre-brief material was  a valuable
exercise, in and of itself and the end product will be useful for the
final CDR.  The  organization of going over the 'dry-runs' for talks in the
weeks  prior to the review was efficient and very productive.
Our collaboration knows how to work well together.  And on
a more personal note, I enjoyed giving my last ever GlueX talk
(sniff, sniff) and feel very satisfied that this review went so
well.  During my remaining two months I will be working closely
with the Regina group on wrapping up our collaborative analysis
(I'll spend a week in Regina in early April) and I will also work on updating
the physics section of the CDR.   Now on to Elton's notes..

Thanks for this nice summary.  I also had a good talk with Stefano
after the close-out session - he's a wonderful and fun person to talk
to - and he knows a lot.  When we talked, we referenced their NIM
article on timing studies they did with a test beam.  The reference is
worth a read:  Antonelli et al, Nucl Inst. & Meth A354 (1995) 352

I plan to continue working with Blake et al on analysis of the test beam
data - I hope by the end of the day to look at resolutions using different
energy weighting options and also using a module PMT (other than one
used in the cluster receiving most energy) as the time reference.
But clearly have to understand the tagger timing as well.  As the data
I showed you indicate - there are still unanswered questions here - but
they should not stop  us for now.

Cheers
Alex

At 11:49 AM -0500 2/21/08, Elton Smith wrote:
>Calorimeter timing enthusiasts,
>
>We spent some time yesterday picking Stefano Miscetti's brain about
>various calorimeter issues, especially timing. He is clearly a walking
>encyclopedia concerning KLOE detector and data. I wanted to pass on a few
>thoughts before I forget.
>
>1. Back of the envelop estimates of the time resolution.
>
>quadruture sum of the following contributions:
>
>1. sigma0 - electronics noise
>2. sigma_sci/sqrt(Npe) - scintillator decay time
>3. sigma_pmt/sqrt(Npe) - intrinsic pmt resolution
>4. sigma_disp/sqrt(Npe) - dispersion
>
>where Npe is the number of photoelectrons. Let us begin by assuming that
>the electronic noise does not contribute (but clearly needs to be tracked
>carefully especially for a large system). Now let us estimate each of the
>other contributions in turn:
>
>2. Sigma_sci. This is determined by the decay time of the scintillator. We
>can take this from the scintillator specifications: 2.7 ns (BCF-20), 3.2
>ns (BCF-12). (Recall that the rms of an exponential is equal to the decay
>time). For discussion take 3 ns.
>
>3. Sigma_pmt. This is given by the transit time spread of the pmt [See
>Philips Photomultipliers Principles and Applications, p. 4-15]. The
>transit time spread is dominated by the variances in transit time from the
>cathode to first dynode (sig_kd1) and the electron multiplier (sig_m). For
>"fast tubes" sig_kd1~0.15-0.35 ns and sig_m~0.15-0.25 ns, giving a
>sigma_pmt~0.21-0.43 ns.
>
>4. Dispersion in the scintillator. This corresponds to transit time
>differences for optical photons traveling at different angles inside the
>fiber. For a maximum trapping angle of 27deg, the transit time difference
>is of order the distance top the pmt (~200 cm)/vsci(20 cm/ns) = 10 ns
>(1/cos13deg-1/cos27deg) ~ 1 ns.
>
>Adding these in quadrature we get 3.2 ns/sqrt(Npe). We see that the time
>resolution will be dominated by the scintillator decay time.
>
>The number of photoelectrons depends on the particle detected. For single
>cells for cosmic ray muons we have measured Npe~25 per pmt. For muons
>traversing 6 cells, we divide by sqrt(6). In the beamtest for 1 GeV
>showers, we estimate a total of 700 p.e. per side.  (This number is
>expected to be 2-4 times higher for the actual detector)
>
>We can now estimate the estimated resolution for the calorimeter.
>
>1 cell: sigma ~ 3.2 ns/sqrt(2*25) = 450 ps.
>muons: sigma/sqrt(6) = 183 ps.
>1 GeV: sigma ~ 3.2 ns/sqrt(2*700) = 86 ps/sqrt(E)
>
>This estimate suggests that our measured time resolution for 1 GeV showers
>is consistent with the energy dependent term but the constant term is a
>mystery. The resolution for muons is espected to be smaller than the
>measured value by a factor of about 2, but consistent with KLOE's
>measurements.
>
>
>Elton Smith
>Jefferson Lab MS 12H5
>12000 Jefferson Ave
>Suite # 16
>Newport News, VA 23606
>elton@jlab.org
>(757) 269-7625
>(757) 269-6331 fax


-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Alex R. Dzierba
Chancellor's Professor of Physics (Emeritus)
Department of Physics / Indiana U / Bloomington IN 47405 / 812-855-9421
JLab Visiting Fellow
Jefferson Lab / 12000 Jefferson Ave / Newport News, VA 23606 / 757-269-7577
Home Phone: 812-825-4063  Cell:  812-327-1881  Fax: 866-541-1263
http://www.dzre.com/alex
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~