Minutes of CMSUK-ECAL meeting, 15-Nov-1994
Minutes of CMSUK-ECAL meeting, 15-Nov-1994
Minutes of the CMS-UK ECAL meeting held at RAL, Tuesday 15 November 1994
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Present: R M Brown (RAL), P S Flower (RAL), G Heath (Bristol),
P W Jeffreys (RAL), B W Kennedy (RAL), D Newbold (Bristol),
C Purves (Bristol), Sabah Salih (Brunel), C Seez (ICST),
R J Tapper (Bristol), T S Virdee (ICST)
1995 Beam Tests
=================
TSV described the plans for next year's beam tests at CERN.
Mechanics
---------
A matrix of PbWO4 crystals will be tested in the H2 or H4 beam; the aim is
to assemble a matrix of at least 6*6 crystals, to 10*10 later in the year.
The readout will use existing Philips PM1911 PMTs, to be supplied by
Katchanov.
CMS has 74 days of beam, divided as follows;
Shashlik 7 days
PbWO4 37
HCAL+VFCAL+quartz+PPC 24
Spare 6
The tests will start in late April or early May.
The PMTs will be mounted on specially-designed plates, also provided by
Katchanov. Similar plates will be needed to mount APDs on the crystals -
these could be designed and manufactured in the UK.
As in the previous beam tests, the matrix will be surrounded by
water-cooled copper plates to stabilise the temperature. CERN will supply
a recycling water cooling system, but not the copper plates which must be
provided by outside groups. The design will need to permit adjustment to
accommodate an array of 36-100 crystals, possibly using spacer plates if
less than 100 are installed. Experience has shown that a dry atmosphere
can be maintained adequately using dessicants.
The whole assembly will be contained in a box, which needs to be designed
and built. The box should allow the use of a preshower layer, which could
be internal or external; in particular, it should be possible to bring the
crystal matrix very close to the side of the box. (The preshower itself is
not a UK responsibility.) Finally, the materials used should be
non-magnetic. All of the hardware should be completed well in advance of
the start of the beam tests in April/May.
A meeting will be held at CERN on 2 December to decide on buying materials
for the tests. It would be very useful for John Connolly to attend this
meeting.
CERN and ETH will buy the PbWO4 crystals.
Electronics and Photodetectors
------------------------------
The plan is to buy 60 APDs from each of EG&G and Hamamatsu, plus some
extras for evaluation and testing. PSI, Ecole Polytechnique, Saclay, ETH,
UK, Lyon, Minnesota, and Fermilab are interested in buying APDs. Lyon,
Ecole Poly and the UK groups are interested in the preamps. The APDs will
ideally have two diodes in a single package to increase the sensitive area.
The crystals are expected to cost about $600 each, for a total of $60000.
The APDs and associated electronics should cost a similar amount.
There was some discussion about the extra cost of double-diode packages,
and the extra light collection to be expected. RMB pointed out that the
gain is less than the factor of 2 in surface area if the crystal face
surrounding the diode is wrapped in reflective material. Furthermore, it
was felt that the suggested cost of 20Sf per double amplifier channel,
which appears to be the CMS cost estimate, was probably optimistic.
TSV emphasised the redundancy achieved with double-diodes. Against this,
RMB argued that independent readout implies extra connectors, and OPAL
experience showed that these are the least reliable components in the
readout chain. However, using independent amplifiers for the diodes might
reduce the noise by 1/sqrt(2) - but this depends on the characteristics of
the APDs.
The issue of temperature control was discussed briefly. It has been shown
that the response of the voltage divider can be made approximately flat
over a range of about 10 degrees by a simple scheme involving resistors of
opposite temperature coefficient. This could be investigated in the UK.
As the CMS endcaps will receive a neutron fluence of 10**15/cm**2 over ten
years (reducing to 10**13 at rapidity=0), the APDs must be irradiated
(with neutrons as well as gammas) to determine the effect of radiation
damage on the leakage currents. Bristol have a large (10 mCi) californium
source which might be suitable, though it remains to be confirmed that the
full 10**15/cm**2 fluence can be achieved in a reasonable exposure time.
The alternative is the ISIS neutron irradiation facility, but RMB
suggested some thought needs to be given to the problem of biassing the
diodes during irradiation.
Presently available evidence suggests the APDs will not survive the 10
years neutron dose expected in the endcap region. If not, suitable vacuum
devices (eg tetrodes) might have to be considered. RAL has considerable
experience with vacuum devices, and also has facilities to test them in
magnetic fields up to 5T.
CMS Responsibility Matrix
=========================
This matrix will eventually match up groups, responsibilities, and money.
For the first iteration however, the money will be replaced by ticks, as
an expression of interest.
TSV proposed to divide the "Electronics" heading into two parts; "front
end", and "very front end", as defined in the CMS draft technical
proposal, and to tick the "very front end" box. This incorporates APDs,
preamps, and the shaping and compression electronics.
The "Mechanics" box was ticked. TSV pointed out that the endcaps are
currently covered only by Russian groups, and that more effort is needed.
Ecole Poly and Rome are interested, as well as IC and RAL.
There was general agreement that the barrel and endcap parts of the ECAL
should be integrated. RMB was concerned that in the current plan the
barrel crystals would be produced first, creating great uncertainties for
the endcaps. In contrast to LEP, at LHC the endcaps have large physics
coverage, and should not be viewed as secondary to the barrel. In
addition, it would be hard to interest groups in a project with such long
delays built in. TSV said that the barrel crystals might be larger than
those used in the endcaps, and so would need a dedicated production
centre; production of the two sizes would then naturally take place in
parallel. RMB urged him to press strongly for an integrated ECAL.
A separate heading was written in, and ticked, for "Test beam
calibration". This is a vital and time-consuming task, which was felt to
be an area where smaller institutions could make a valuable contribution in
manpower without making large investments of money.
The "Assembly and Installation" box was ticked. This led to a discussion
of RAL acting as a regional centre within CMS. RMB said that this is not
in line with present RAL philosophy, and that less manpower is available
than in the past. However, John Connolly should be asked to look into the
planning and resources needed. The role of University groups would be
important, both in providing technical and workshop effort, and in system
testing and diagnostics. Some of the work might be rather unskilled;
crystal wrapping was given as an example. On the other hand, quality
control and test measurements could be appropriate work for graduate
students and technical support staff. PWJ emphasised that considerable
effort would be needed to share information between groups, particularly
in the form of databases, and complete histories of components being
built and tested.
TSV estimated that a quarter of the ECAL (9/36 barrel modules) could be
built in the UK. Bristol expressed interest in the proposal, and expects
to have some technical effort available for this task. Also, the UK could
take responsibility for the preamps and tetrodes (some negociation with ETH
may be needed here).
Budget
========
RMB described the state of the CMS budget for the 18 months to April 1995.
The PPSP allocated a total of #160k (# = pounds); #90k for the tracker,
and #70k for the ECAL. #3k was spent last year, and #31.7k is known to
have been spent this year, leaving approximately #125k to carry over. GH
said that some of the tracker commitment has not yet appeared in the
financial tables. He expected to spend most of the tracker allocation by
the end of this financial year.
Other Tests Next Year
=======================
RMB briefly described measurements made recently on the light yield of
PbWO4 in the ISIS test beam, and progress made by Geoff Grayer on
determining the emission spectrum using a radioactive source and a
monochromator (believed to be on loan from Bristol). Geoff has measured
the spectrum of a plastic scintillator, and it is hoped that he can make
the much more difficult PbWO4 measurement soon.
Radiation hardness measurements on the APDs will be made at Bristol and RAL
using neutrons, and at Brunel using gammas. TSV remarked that the
quantum efficiency of the APDs must be determined.
NIM papers
============
The PbWO4 paper (responsibility of TSV and CS) can wait until after the
open presentation. The paper should be ready at the end of January 95,
and will concentrate on the results obtained with large crystals at CERN.
RMB mentioned the RAL measurement of the temperature dependence of the
photon yield; this might be included in the fluorohafnate glass paper.
TSV suggested a separate paper on the properties of PbWO4, including
temperature dependence, radiation damage, etc. This needs discussion with
LeCoq, Katchanov, etc.
********************************************************************************
Minutes of the CMS-UK General meeting held at RAL, Tuesday 15 November 1994
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Present: R M Brown (RAL), G Hall (ICST), W J Haynes (RAL),
G Heath (Bristol), P W Jeffreys (RAL), B W Kennedy (RAL),
D Newbold (Bristol), C Purves (Bristol), Sabah Salih (Brunel),
C Seez (ICST), R J Tapper (Bristol), T S Virdee (ICST)
(+ 2 from Bristol),
UK Names for the Technical Proposal
=====================================
Michel Della Negra has asked for a list of signatories from all CMS
groups; physicists, engineers, and students are eligible, but not
technicians. Most of the UK groups have responded; the RAL reply has been
delayed to decide which of the RAL engineering support staff should be
included, and how to divide the names up appropriately between CMS and
Atlas.
Our Policy for Seeking UK Funding Beyond March 1995
=====================================================
RMB distributed copies of a note he has received from Derek Imrie, and his
reply. Derek has recently spoken to David Saxon and Mike Green, who would
like a meeting with UK group leaders. There is pressure from Atlas to
hold a PPESP meeting before the next scheduled one late in March to
discuss funding. It was felt that CMS would not need an early meeting,
provided that there was a prompt decision after 20 March. GH saw
advantages in advancing the date, as the tracker group has several large
spending commitments planned for electronics. If the decision were delayed
a provisional allocation of "discretionary funds" might be needed to avoid
a hiatus in the project. For the ECAL and trigger, TSV and WJH favoured
March.
** ACTION TSV ** TSV will talk with David Saxon next week at CERN to
arrange a meeting with the UK group leaders, and to
find out what information he will require from us.
UK Contributions to the Common Fund
=====================================
The CMS spending profile planned in the UK allowed for a sizeable increase
in expenditure in 1995. However, the LHC schedule has slipped back.
Nevertheless, CMS would favour an early contribution to the common fund in
order to make a start on the magnet design, which is on the critical path
of the experiment according to current planning. George Kalmus, Michel
Della Negra, and Diether Blechschmidt have already met to discuss this
possibility.
It is not obvious that this money will in fact be available since no
formal allocation has been made for next year, but there was some
discussion on the assumption that there would be extra money next year.
The common fund represents a proportion (still to be determined) of each
country's total contribution to CMS. The UK total is #6M, so guessing
that the common fund proportion will be 30%, #1.8M of this will go to the
common fund. The arguments in favour of an early contribution were: it is
needed for the magnet design; exchange rate variations and inflation might
make it more difficult to meet our agreed contribution in later years; it
should produce credit (or at least goodwill) within CMS. The principal
argument against was that such goodwill might not be long-lasting. After
discussion, there were reservations, but no explicit opposition to
contributing next year if the money is available.
Filling in the CMS Responsibility Matrix
==========================================
This item was discussed in some detail in the ECAL meeting (see previous
minutes). RMB distributed a projection of resources required per year for
CMS from the present to 2003/2004. The most worrying feature of this was
the travel budget.
UK Travel Budget
==================
In the enforced absence of Dave Cockerill, RMB described the state of the
travel budget as far as he had been able to ascertain. Of the #63k
allocated for this year, #52k had already gone by 4 November. RAL is
overspent, ICST is close to exhausting its budget, while Bristol and
Brunel have not yet spent their (small) allocations. It is clear from
several discussions with George Kalmus that no extra money will be
forthcoming to cover the shortfall, and any overspend will be debited to
the CMS capital allocation. The position is therefore very serious;
groups are asked to travel as little as they can, and where possible to
fit in CMS business during trips mainly devoted (and charged) to other
experiments.
Date of Next Meeting
======================
The next meeting was provisionally arranged for 31 January 1995, again
to be held at RAL.
B W Kennedy
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