1. Digital Calorimetry using GEM technology Andy White for UTA group
(A. Brandt, K. De, S. Habib, V. Kaushik, J. Li, M. Sosebee, Jae Yu)
6/28/2002

2. Goals
Develop digital hadron calorimetry for use with energy flow algorithms
Develop flexible, robust design
Design GEM cell(s) and prototype
Develop module/stack design
Simulate GEM behavior
Develop simulation software and energy flow and cal tracking algorithm(s)

3. Requirements for DHCAL
General
Thin sensitive/readout layer for compact calorimeter design
Simple 1- or 2-level “hit” recording for energy flow algorithm use
On-board amplification/digitization/discrimination for digital readout – noise/cross-talk minimization
Flexible design for easy implementation of arbitrary “cell” size
Minimal intrusions for “crackless” design
Ease of construction/cost minimization

4. (B) Gas Amplification Specific - Sufficient gain for good S/N
- Minimized cross-talk between “cells”
- Readout path isolated from active volume
- 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)
- Keep HV low for safe/reliable use
- Keep electronics simple = cheap/reliable

5. (c) Energy flow requirements
- small cell size for good two/multiple track separation
- high efficiency for MIPs in a cell
- option for multiple thresholds
- non-alignment of dead areas for efficient track following

6. GEM (Gas Electron Multiplier) Approach
GEM developed by F. Sauli (CERN) for use as pre-amplification stage for MSGC’s.
GEM also can be used with printed circuit readout – allows very flexible approach to geometrical design.
GEM’s with gains above 104 have been developed and spark probabilities per incident  less than
Fast operation -> Ar CO2 40 ns drift for 3mm gap.
Relatively low HV (~ few x100V per GEM layer)
(cf kV for RPC!)

7. Double GEM schematic
From S.Bachmann et al. CERN-EP/

8. From CERN-open-2000-344, A. Sharma

9. Micrograph of GEM foil
From CERN GDD Group

10. Detail of GEM foil hole
From CERN GDD Group

11. GEM foils Most foils made in CERN printed circuit workshop
Approximately 1,000 foils made
Big project for COMPASS expt. 31x31 cm2 foils
Most difficult step is kapton etching – Sauli has offered to reveal “trade secrets” in context of formal collaboration.
Fastest route – buy a few foils from Sauli:
10x10 cm2 foils 70m holes 140m pitch ~$300
- Foils HV tested/verified at CERN.

12. GEM gains
From CERN GDD group

13. GEM amplification vs. metal hole size
from A. Sharma CERN OPEN

14. Initial design concept for gas amplification DHCAL using GEMs

15. Readout schematic Digital/serial output Anode pad Ground AMP DISC AMP
thr
thr
AMP
DISC
AMP
DISC
REG
REG
Digital/serial output

16. GEM test chamber ( J.Li, UTA )

17. Detail of GEM prototype chamber
- pad contact

18. GEM prototype – readout path

19. Single GEM gain/discharge probability
A.Bressan et al
NIM A424 (1998) 321

20. from A. Sharma CERN OPEN-98-030
GEM aging study
from A. Sharma CERN OPEN

21. UTA Simulation Plans
Working with NIU/SLAC to develop GEANT4 based simulation
Investigating GEANT4 – CAD linkage for easier implementation of geometry
Use for detailed cell/module design
Simulate performance of GEM cells for single particles and hadronic showers
Develop Energy flow and cal tracking algorithms using GEM based had-cal

22. UTA Simulation Status Two graduate students working on this
Currently Gismo installed but having linking problem due to xml library setup
Mokka installed for the use of Geant4
Having growing pain…
Will generate events using existing geometries in Gismo and Mokka to get familiar with the tools and analysis
Implement prototype GEM cell geometry
By hand initially, moving slowly into CAD
At the lower end of learning curve

23. UTA R+D Plans Now supported by DOE ADR !
Develop GEM calorimeter cell design
Understand GEM issues (discharges,…)
Develop module design/readout
Build/operate GEM test chamber(s) (with local support)
Simulate performance using GEANT4 and other MC tools  Having growing pain
Develop EF and cal tracking algorithms