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.