Date: Thu, 07 Aug 1997 19:13:17 +0200
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Subject: Questions from LHCC Referees on the HCAL TDR
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Appended are the questions received from the LHCC HCAL referees. Dan Green
(dgreen@fnal.gov) is coordinating our answers to these questions. Please
send your input to Dan ASAP - our response to the referees is due August 28.

                                                - Jim Hanlon

Return-Path: <h02@nikhef.nl>
Resent-date: Mon, 04 Aug 1997 07:19:26 -0500 (CDT)
Date: Mon, 04 Aug 1997 14:18:52 +0200
Resent-from: dgreen@FNALV.FNAL.GOV
From: h02@nikhef.nl (Jos Engelen)
Subject: HCAL TDR
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To: dgreen@fnalv.fnal.gov
Cc: IAROCCI@LNF.INFN.IT, Michel.Della.Negra@cern.ch, Mike.Sendall@cern.ch,
 calvetti@fi.infn.it, dionisi@vxrm64.roma1.infn.it, j.engelen@nikhef.nl,
 kolanosk@ifh.de, mont@d0sgi0.fnal.gov, read@fys.uio.no, strait@FNAL.GOV,
 tejinder.virdee@cern.ch, wormser@frcpn11.in2p3.fr
Resent-message-id: <01IM17RZECR8000V9R@FNAL.FNAL.GOV>

Dear Dan,

Following is a list of questions on the HCAL TDR.
Could you PLEASE FORWARD them to your colleagues
on the HCAL team and to others who you want to
involve in answering them.

The questions resulted from discussions between Dionisi,
Wormser and myself. Additional questions were
submitted by Calvetti (consultant) and a few more
were generated by other members of the LHCC during
the last meeting.

Carlo Dionisi might have additional questions. If
that is the case they should reach you before the
end of this week.

As you know we (referees+consultant(s)?) have planned
a meeting with CMS on August 28.

                            With kind regards, Jos Engelen


Questions by LHCC referees and consultants on CMS Hadron
Calorimeter Technical Design Report (CERN/LHCC 97-31)
--------------------------------------------------------

                                               August 4, 1997

- Energy resolution: what is the design goal? Give both HCAL stand-alone
  performance and performance in CMS.
- Spatial (transverse) resolution: what is the design goal?

-- In view of the above: discuss the measurement of H --> b bbar
   as a bench mark.

- Discuss the intercalibration of the various calorimeter
  longitudinal sub-sections, in particular of the outer
  calorimeter w.r.t. the 'inner' calorimeter. Same for
  the scintillator in between ECAL and HCAL.
- Discuss the monitoring of these extensions of the calorimeter.

- HPD's: present an R&D plan towards a prototype meeting
  the requirements. (gain; risetime; number of pixels;
  failure mode analysis (can one pixel die without
  affecting the rest); price)
- HPD's: is the direction of the B field w.r.t. the HPD's
  known with sufficient certainty and at all locations,
  to warrant an optimal orientation?

- What are the timing capabilities of the calorimeter, i.e.
  what is the resolution on the measured arrival time
  of a signal? This question also refers to HF.

- HF: quartz fiber procurement: is this an issue? Is it
  foreseen to have more than one provider?
- HF: how will the magnetic shielding of the PM's be
  achieved?
- HF: how was its longitudinal position optimized? Bringing
  it in towards the interaction point would allow to make
  it smaller.
- HF/HE transition: how does the calorimeter response in
  this region look?

- Depth of HB: when will the definitive decision on the
  depth of HB (5.15 versus 5.82 lambda) be made? Is the
  smaller depth acceptable?

- The sampling gap (in particular HB):
  . how has the lay out of this gap been optimized,
    in particular w.r.t. scintillator thickness
  . shouldn't you be more demanding on the tolerance
    on the scintillator thickness? (0.4 mm on a thickness
    of 4 mm).
  . is the lay out of the sampling gap compatible with
    the anticipated mechanical deformations?
- The effect of the B field // absorber plates:
  . are you sure you understand this effect quantitatively?
    Is there also a 'back splash' effect, i.e. is it
    important to also stay clear from the absorber plate
    following the sampling gap (and by how much?)
    (Fig. 6.17 and Table 6.2 look incompatible as far
    as the position of the thick, 1.9 mm, plastic layer
    is concerned.)
  . Tolerance on scint. thickness once again: thin scint.
    is further from aborber plate: two correlated reasons for less
    light. Thick scint. is closer to absorber plate: two
    correlated reasons for more light.
  . Is this newly discovered dependence on B// independent
    of the energy of the hadron being absorbed?

- HE: give a drawing of a scintillator tile, including the
  embedded WLS. Comment on the uniformity of response.

- Magnet trips: HE takes precautions. Is this critical, i.e.
  are you sure these precautions are sufficient? What about
  HB?
- Finite Element Analysis of HB, HE. The approach for HB and
  HE looks somewhat different. HB is analysed under static
  loads only. For HE horizontal and vertical accelerations
  are applied in addition. Why these differences?
  The HB model allows larger deformations than possible
  in reality (p. 111), will this not lead to an underestimate
  of forces and stresses? For what it is worth: the key ways
  (HB) have to 'help' the bolts resist shear forces. Does
  this really work? (I would say: either the bolts or the
  key ways take the force.)

- Radiation damage of scintillator: is it foreseen to replace
  the scintillator in HE from time to time?

- I have not found in the TDR a clear indication of the deterioration of the
  signal to noise ratio, for the Higgs search, due to the pile up noise.
  I understand that the time structure of the machine and the memory time
of the
  detectors are such that one event occupies three (or more may be) clock
  cycles at 40Mhz.
  In the TDR there is no evidence that the detectors, scintillators,
  fibers, etc, have the necessary speed.
  What is the deterioration of the signal to noise ratio ( for the Higgs )
if
  the memory time of the system is 100nsec?
  In the calculation of the backgrounds are the accidentals considered?

- Pag 38 fig.1.15  dijet mass distribution. What does it look like with the
  underlying background? What is the effect of pile up, including physical
  background, if the memory time of the detector is longer than anticipated?
  WHAT IS THE MEMORY TIME OF THE DETECTOR? in the barrel, endcap and forward.
  Are there long time constants in the read-out chain?

- MUON SIGNAL
  the 10 photoelectrons expected for muons are distributed in time because of
  the loop of the fiber in the tile. The loop lenght is about 70-80 cms
  corresponding to about 5-6 nsec to be convoluted with the relaxation
  time of the plastic scintillator( not found by me in the TDR ).
  Is the spread of the arrival time of the single photoelectron signals
  critical for the efficiency for the detection of the muons
  (threshold at 4 p.e)?
  In a random event, that is in one beam  crossing, how many towers have more
  than three photoelectrons in the time associated to the event?

- The fibers are running parallel to the shower to reach the read-out box.
  What happens if the shower hits the fibers?

- Electronics etc.
 . is the packaging of the electronics fully optimized?
 3 channels/chip
 50 VME crates for only 15,000 channels
 16 racks  p.503
 . I do not understand the requirements in HF concerning the noise floor
 (p.408). Working with a single photoelectron, the threshold should be
 set at 20% p.e. due to the PMT dispersion. The noise floor should then
 be a fraction i.e. 1/3 of this). So the noise floor is more 6% of p.e.
 rather than 25%. In this case with a gain of 40,000 it means 2400 e-.
 (actually similar to HB,HF requirements)
 . how critical is the gain 2000 for the HPD (p.408)
 . the proposed grounding scheme requires isolation from the detector
 at every step. How well does the cooling system comply with the
 grounding scheme?
 . To which extent does the radioactive source detection impose a burden
 on the electronics
 . could you develop further the arguments (including cost) why a
  Cockcroft-Walton system is better than a resistive base system?
 . The granularity of the HV for HPD seems too coarse :1 HV for all
  HPD in the same box (large chunk missing in case of failures) p.486
 . We concur of course with the importance of assessing QIE chip
  radiation resistance.
 . to which precision is the power dissipation known (210 Watts) given the
  uncertainty mentioned above in the final QIE technologyy. What is
  the present flexibility of the cooling systemn in case of significant
  heat increase?
 . what are the consequences of leaks in the cooling system. Do you have
  to go to a leakless sytem? what would be the associated cost increase?


                                        Edited by Jos Engelen




Dan Green
US CMS Spokesperson
CMS Dept. ms 205
WH6NW Fermilab Batavia, Il
phone 630-840-3104
(FAX)        -2194
e-mail dgreen@fnal.gov
A.A. Terry Grozis, - 3854