Update on

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Update on GEM-based Calorimetry for the Linear
Collider

• White 1/11/03
• (for J.Yu, J.Li, M.Sosebee, S.Habib, V.Kaushik)

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Summary of criteria for GEM-based LC Calorimetry

• Thin sensitive/readout layer for compact
  calorimeter design
• Simple 1- or 2-level hit recording for energy
  flow algorithm use
• On-board amplification/digitization/discriminatio
  n for digital readout noise/cross-talk
  minimization
• Flexible design for easy implementation of
  arbitrary cell size

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Criteria continued
- Modular design with easy module-to-module
continuity for supplies, readout path -
Digital readout from each cell - Pad design (to
avoid x-y strip complications) - small cell size
for good two/multiple track separation - high
efficiency for MIPs in a cell - option for
multiple thresholds
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Design for DHCAL using Triple GEM
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UTA Approach to GEM/Calorimetry

• Two-prong approach
• - Simulate, in detail, stack of GEM
  hadron calorimetry (see V.Kaushiks talk)
• - Develop practical experience assembling
  a GEM foil based detector from scratch.

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From CERN-open-2000-344, A. Sharma
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GEM gains
From CERN GDD group
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Double GEM schematic
From S.Bachmann et al. CERN-EP/2000-151
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Areas of GEM related study

• GEM foil handling, testing, installation.
• GEM double layer structure design and
  implementation.
• HV distribution system design implementation.
• GEM anode pad design, variations, testing.
• Readout electronics trials
• Complete prototype assembly, testing.

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GEM prototype assembly
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GEM FOILS (testing)

• Foils for prototype purchased from GDD group at
  CERN (400 each framed)
• Initial experience foils are fairly robust we
  have so far only exposed them in clean room
  environment care with human exposure!
• Electrical testing first test HVPS with ?A
  meter -gt discharge -gt local damage to 5 holes -gt
  fix with copper etch locally.
• nA level current monitoring -gt easily reach 450V
  across foils in air repeatable.

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GEM FOILS (production)

• Calorimeter and tracking groups in U.S.
  interested in GEM-based detectors.
• Clearly U.S. source would be preferable.
• Potential sources
• 3M Thin Films, MIT ?, Louisiana Tech.?
• Issues - etching vs. micro-machining etc.?
• - only limited quantities needed
  for HEP
• - interest from medical imaging ?
• - hole size, shape, quality for HEP
  use?

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Micrograph of GEM foil
From CERN GDD Group
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GEM foil issues
 
Defects in chemically etched GEM foils, showing
misshaped and missing holes. Taken from F. Fraga
et al. NIM A442, 417, 2000
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Detail of GEM foil hole
From CERN GDD Group
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GEM amplification vs. metal hole size
from A. Sharma CERN OPEN-98-030
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GEM test chamber ( J.Li, UTA )
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GEM/MIP signal size

• Double GEM 2100V -gt Gain 3000
• Ionization 30 i.p./cm gt 10 e- / MIP
• This gives 30,000 e- on an anode pad.
• 30,000 e- 5 fC
• GEM signal timing 20ns
• Current 5fC/20ns 0.25 ?A
• Amplifier sensitivity 25 mV/?A
• Expect signals 5mV for MIP through GEM

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Anode pad layout
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GEM Prototype Status

• GEM chamber assembled/re-assembled several times
  to optimize layer spacing, HV stability, ...
• Initially large noise problems (from building)
  now mainly suppressed through grounding,
  filtering, sheilding.
• Testing 1) Cosmic rate is 0.1 Hz through 6 cm2
  pad
• 2) Source Cs-137 e-
  1 MeV vs. GEM board
• - See signals not yet uniquely attributable to
  GEM.