Digital Calorimetry using GEM technology Andy White for UTA group (A. Brandt, K. De, S. Habib, V. Kaushik, J. Li, M. Sosebee, Jae Yu) CALICE/CERN 09/23/2002

Goals  Develop digital hadron calorimetry for use with energy flow algorithms  Develop flexible, robust design  Design GEM cell(s) and build prototype  Develop a digital readout/minimize size  Develop module/stack design  Construct stack for test beam

Goals  Simulate GEM behavior in relation to DHCAL: shower energy deposition, spiraling e -, …  Develop simulation software for energy flow and cal tracking algorithm(s)

Requirements for DHCAL (A) 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

(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

(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

Design for DHCAL using Triple GEM Ground to avoid cross-talk Embeded onboard readout

GEM (Gas Electron Multiplier) Approach GEM developed by F. Sauli (CERN) (initially 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 10 4 have been developed and spark probabilities per incident  less than Fast operation -> Ar CO 2 40 ns drift for 3mm gap. GEM’s detect fast electron charge (not slow ions) Relatively low HV (~ few x100V per GEM layer) (cf kV for RPC!)

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

From CERN-open , A. Sharma

- Most foils made in CERN printed circuit workshop - Approximately 1,000 foils made - Big project for COMPASS expt. 31x31 cm 2 foils - Most difficult step is kapton etching – possible collaboration with F. Sauli on foil fabrication - Fastest route for now – buy a few foils from Sauli: 10x10 cm 2 foils 70  m holes 140  m pitch ~$300 - Foils HV tested/verified at CERN. - U.S. interest in foil production (MIT, Purdue, Louisiana Tech.) – for LC/TPC application GEM foils

Micrograph of GEM foil From CERN GDD Group

Defects in chemically etched GEM foils, showing misshaped and missing holes. Taken from F. Fraga et al. NIM A442, 417, 2000 GEM foil issues

Detail of GEM foil hole From CERN GDD Group

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

Study of GEM aging From: C.Altunbas et al. (COMPASS) NIM A490 (2002) 177

From CERN GDD group GEM gains

Design for DHCAL using Triple GEM Ground to avoid cross-talk Embeded onboard readout

Possible variations on GEM design -> Easy variation of pad sizes/shapes - optimize pad size/layer/depth -> Option to use cheaper 2-D readout (strips) -> Option for precision tracking layers inside calorimeter (i.e. GEM cal. + GEM tracking) -  ’s in the calorimeter (e.g. b ->  - # of measurements (GEM layers), precision (40  m in COMPASS) ?

Readout schematic AMPDISCAMPDISC REG Digital/serial output thr Anode pad Ground

GEM prototype  Basic GEM cell for understanding, development, and studies of operating parameters  Flexible prototype design: - variable number of GEM layers (1, 2, 3) - variable readout pad sizes, shapes - tests of readout path schemes - use Ar/CO 2 70:30  Source/cosmic tests

GEM test chamber ( J.Li, UTA )

Detail of GEM prototype chamber - pad contact

GEM prototype – readout path

GEM prototype status  Body of chamber made  GEM foils (2) received from CERN (2 more foils “ordered”.  First readout pad board made  HV scheme under design  Readout electronics in hand: - LeCroy HQV800 series charge preamps - LeCroy 2735 discriminator

 Clean room in UTA NanoFab facility available for GEM handling and assembly  Estimate 2-3 weeks for completion of prototype and start of initial tests.

GEM prototype assembly

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

DHCAL/GEM module design  Working on DHCAL/GEM unit module ideas  Exploring multiple module/absorber gap: HV, LV, CTRL signal

Issues  Keeping GEM layer thin ~6 mm  Practical module size vs. foil support(s)  Module-module interconnections: - HV distribution - LV for amplifier/discriminator - signal extraction - robust design

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

-Two graduate students working on this -Mokka installed for the use of GEANT4 -Uses remote DB for geometry -Generated 1,000 t tbar events using existing geometry in Mokka to get familiar with the tools and analysis -Looking at hits/energy/cell -Implement prototype GEM cell geometry -By hand initially, moving into CAD UTA Simulation Status

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) - Simulate performance using GEANT4 and other MC tools - Develop EF and cal tracking algorithms - Interested in DHCAL collaboration!