Update on GEM-based Calorimetry for the Linear Collider A.White 1/11/03 (for J.Yu, J.Li, M.Sosebee, S.Habib, V.Kaushik)

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/discrimination for digital readout – noise/cross-talk minimization - Flexible design for easy implementation of arbitrary “cell” size

- 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 Criteria continued…

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

UTA Approach to GEM/Calorimetry  Two-prong approach - Simulate, in detail, stack of GEM hadron calorimetry (see V.Kaushik’s talk) - Develop practical experience assembling a GEM foil based detector from scratch.

From CERN-open , A. Sharma

From CERN GDD group GEM gains

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

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.

GEM prototype assembly

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 -> discharge -> local damage to ~5 holes -> fix with copper etch locally. - nA level current monitoring -> easily reach 450V across foils in air – repeatable.

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?

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

GEM test chamber ( J.Li, UTA )

GEM/MIP signal size - Double GEM ~2100V -> ~ Gain Ionization ~30 i.p./cm => 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

Anode pad layout

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 cm 2 pad 2) Source Cs-137 e- ~1 MeV vs. GEM board - See signals … not yet uniquely attributable to GEM.