Minutes of CMSUK-ECAL meeting, 11-Jul-1996
Minutes of CMSUK-ECAL meeting, 11-Jul-1996
Minutes of UK CMS/ECAL Meeting; 11 July 1996, RAL
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Present: K Bell (RAL), R Brown (RAL), D Cockerill (RAL),
G Davies (ICSTM), P Flower (RAL), R Head (Bristol),
G Heath (Bristol), H Heath (Bristol) P Hobson (Brunel),
B Kennedy (RAL), D Newbold (Bristol), U Schaefer (Bristol),
M Sproston (RAL)
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Minutes: B W Kennedy / RAL
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1) ECAL money matrix and other financial matters.
RB stated that money matrices will be prepared for each subdetector
for the Aachen meeting, but only at "Level 3" - which means a broad
summary of expenditure without enough detail to be really useful. In
principle the matrix should be proposed by the Institution Board, but
in RB's view this was unlikely in the ECAL case. A more detailed
breakdown will be needed by the ECAL group in order to produce
meaningful figures for this matrix. The "Level 4" matrix is tied to
the submission of CORE version 8 in Feb 1997.
DC had heard that, with the retirement of Detlev Schmitz, Germany
would no longer contribute to the ECAL. RB confirmed this; 3MSf of
German money which was expected to go to the ECAL and TRIDAS will now
be spent on the tracker instead. However, it is expected that the
shortfall will be made up by a redistribution of Swiss money. DC will
confer with Hans Rykaczewski to ensure that UK intentions are
integrated into the overall planning. The planned UK expenditure must
be matched to the needs of the experiment.
DC remarked that Ecole Polytechnique have no industrial contacts for
the manufacture of alveolar structures. John Connolly has some ideas
for industrial production involving British and Belgian companies, so
the UK could make an important contribution in this area. RB stressed
the need to pursue investment in UK industry aggressively, but warned
against diverting significant resources away from the Regional Centre
to advance the work of another group. DC will find out what JC has in
mind, and get an estimate of the cost.
2) Future meetings and Regional Centre preparations.
GH said that space will soon become available in Bristol, and he needs
more information about Regional Centre needs in order to prepare a
bid. Suitable areas have already been earmarked at IC and RAL. It
was agreed that a Regional Centre meeting should be held at RAL on
26/7/96.
GH suggested that future meetings should include reports on work
connected with the ECAL, tracker, trigger, daq, etc in addition to
the usual financial and administrative issues. DC was happy to
oblige, if suitable talks are suggested to him.
3) Non-imaging concentrators
PH gave a short talk based on the note he had already circulated. He
concluded that reflective "compound elliptical" concentrators, which
are well-understood theoretically, give little prospect of substantial
improvements in light collection. This depends in part on the
variation of the APD quantum efficiency as a function of angle of
incidence; no data seems to be available on this question. It is
possible to gain by a factor of n**2 if the concentrator is made out
of a dielectric of refractive index n, and coated to ensure complete
light reflection. Recently, more complicated concentrators have been
described in the literature which might offer some advantages.
GD presented some results from a Monte Carlo simulation of light
collection with various concentrators. He found that a glass or PbWO4
prism actually degrades the light collection, and better results were
obtained by placing the APD directly on the end of the crystal. This
is believed to happen through reflection of light back into the
crystal from the sides of the prism. RB remarked that Geoff Grayer
had suggested a Fresnel lens, possibly ground onto the rear face of
the crystal. This has been tried experimentally by Jean-Pierre
Peigneux, and no improvement has been seen. DC recalled a suggestion
from Paul Baillon that a factor 3 might be gained by attaching the APD
to the crystal by van der Waal's forces instead of gluing it. PH
objected that this would be thermally unstable, while HH thought that
the preparation of the surfaces would be much too time-consuming.
GD's simulation suggests that direct coupling increases the light
collection by a factor 2 over an air gap.
PH was still keen to purchase radiometric software to investigate more
complex geometries, despite the hostility of CMS when he had raised
the suggestion at CERN. Unfortunately such packages cost several
kpounds, and it was not clear where the money could be found.
Finally, PH pointed out that most of the problems arise because the
APD has a flat active surface, and that much better light collection
could be achieved with, eg, a hemispherical VPD.
4) Noise measurements at ISIS.
MS described recent work at the ISIS test beam. A new CAMAC-based
readout system was now in place, sending data directly to a PC. In
lab conditions, the PAD noise level was found to be ~1000 electrons
RMS. In the test beam area this increased to 1250 with the magnets
off, and 1300 with magnets on. Both ISIS and the HEP beam-line had
problems, but some pulses had been seen from the APD using NE110.
AOB)
None.
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