1. Status of the CMS GEM Project
Michael Tytgat on behalf of the CMS GEM Collaboration
RD51 Collaboration Meeting, October 16, 2013
Outline
Introduction
CMS Muon Trigger motivation
Detector construction and tests
Production quality control
Integration into CMS
DAQ and Electronics
Towards LS3
October 16, 2013
M. Tytgat - RD51 Collaboration Meeting

2. M. Tytgat - RD51 Collaboration Meeting
The CMS GEM Project
Install triple-GEM super chambers (double stations) in 1.6<|η|< endcap region:
Restore redundancy in muon system for robust tracking and triggering during HL-HLC
Improve L1 and HLT muon momentum resolution to reduce or maintain global muon trigger rate
Ensure ~ 100% trigger efficiency in high PU environment
GE1/1
GE2/1
LS3
LS2
GEMs: R&D Project CMS 10.02; The LS2 Project
October 16, 2013
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Project Milestones
OVER FOUR YEARS OF R&D
Small prototypes, bench tests; picked GEMs among MPGDs for further study
Established space and time resolution achievable
First Large-area GEM foils produced with Single Mask technology
First large-area GE1/1 prototype; beam test
2011
Second redesigned GE1/1 prototype (smaller gaps b/w GEMs)
“GEM Collaboration (GEMs for CMS)” constitutes itself in May CMS week (76 collab. from 15 inst. )
Summer beam tests (including first test in CMS test magnet)
Established 100µm (300µm) res. with analog (binary) r/o chip
NS2 GEM foil assembly technique w/o spacers
Preliminary electronics design starts
October 16, 2013
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Project Milestones
2012
Beam tests – Magnetic Field Operation and fine space and time resolution on large size established
Working Groups
Detector Hardware
Physics Studies
Trigger Simulations
Detector Physics Group
Integration and Services
Electronics & DAQ
Online Operation
Collaboration Expanded 42 Institutions, 183 collaborators EOI, ~ 75 authors
6 GE1/1 full size NS2 detectors produced
CMS approval for installation of GE1/1 demonstrator, i.e. 2 Super Chambers covering a 20° sector in YE1/1 during LS2 (2x36 Super Chambers = 144 triple-GEMs)
“Motivation” plots approved by CMS
GE1/1 TDR on track
2013
October 16, 2013
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5. M. Tytgat - RD51 Collaboration Meeting
GE-1/1 proposal for LS2
Proposal calls to instrument the part of first muon station closest to the beam with a set of triple-GEM chambers:
Highest rates in the entire system
Only CSCs, no redundancy
RPC coverage ends at |η|=1.6
ME1/b
GE1/1
ME1/a
Even chambers
Odd chambers
October 16, 2013
M. Tytgat - RD51 Collaboration Meeting

6. CMS Muon Trigger Challenges
Forward region |η|>1.6 trigger relies entirely on the CSC system
General trend is lowering efficiency towards higher eta to compensate for higher background rates
Optimal operating point is a function of PU (7 and 8 TeV are different)
CSC is a superb system but it is not PU-proof:
Efficiency losses grow with PU
High L1 trigger rates in the very forward region
L1 trigger rates “flattening”
The period between LS2 and LS3 is the most difficult time:
Current system at the edge and the foreseen L1 Tracking Trigger is not yet online
October 16, 2013
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Forward Muon Trigger
Muon momentum from stub positions
ΔφXY=φ(ME-X)-φ(ME-Y)
Measurement driven by Δφ12: ME-1/1 “drives” precision (least scattering)
Slow turn-on:
Efficiency plateau is 20-25% above L1 threshold
“Flattening”: mismeasured soft muons
Soft muons scattering in the absorber can occasionally have stubs aligned like for a high pT muon (rare, but lots of soft muons); tails in L1 momentum resolution
Only two handles on pT mismeasurements:
Nstubs (out of 4) and ME-1/1 stub presence; both are used to define quality of the CSC TF tracks (used in GMT)
Can’t push too far without large efficiency losses
PU reduces trigger efficiency by few %
91% plateau
Zero PU
October 16, 2013
M. Tytgat - RD51 Collaboration Meeting

8. GEM-CSC “Bending Angle”
View from the top of CMS down
L1 muon momentum resolution can be improved with a second muon system, allowing to measure the “bending angle”
A GEM detector in YE-1/1 (the least affected by scattering, largest B)
Increase “lever arm” from 10cm to Δz=30-50cm (physical constraints)
Need ~2 mm or better trigger resolution to effectively discriminate 5 GeV from 20+ GeV muons
October 16, 2013
M. Tytgat - RD51 Collaboration Meeting

9. M. Tytgat - RD51 Collaboration Meeting
Detector Hardware
2013/14
2010
2011
2012
2013
Generation I
The first 1m-class detector ever built but still with spacer ribs and only 8 sectors total. Ref.: 2010 IEEE (also RD51-Note )
Generation II
First large detector with 24 readout sectors (3x8) and 3/1/2/1 gaps but still with spacers and all glued. Ref.: 2011 IEEE. Also RD51-Note
Generation III
The first self-stretched sans-spacer detector, but with the outer frame still glued to the drift. Ref.: 2012 IEEE N
Generation IV
The current generation that we have built two of at CERN so far, with four more to come from the different sites. No more gluing whatsoever. Upcoming papers from MPGD 2013
and IEEE2013.
Generation V
The upcoming detector version that we will install. One long and one short version. Optimized final dimensions for max. acceptance and final eta segmentation.
October 16, 2013
M. Tytgat - RD51 Collaboration Meeting

10. Full-size GE1/1 Detectors Developments in Time
2013/14
2010
2011
2012
2013
QC of Production GE1/1 chambers with final electronics
Production and QC of detectors
First prototype of VFAT3
Slice installation
Slice and trigger commissioning
2014/15
2015/16
2016/17
2017/18
2018/19
Full installation of GE1/1 with final electronics
Full-production of
chambers and electronics started
October 16, 2013
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Current GE1/1 Detectors
Single-mask & self-stretching techniques
Gap sizes: 3/1/2/1 mm
Sectors : 3 columns x (8-10) η partitions
Strip pitch: mm
1D readout of up to 3840 channels
35 HV sectors
October 16, 2013
M. Tytgat - RD51 Collaboration Meeting

12. NS2 Self-Stretching Technique
October 16, 2013
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Detector Frames
External frame :
Originally made of 8 pieces, glued together; gave problems to fit onto PCB, 2 days needed for gluing and hardening
Present version made of 1 single piece, with special tool to dril lateral holes
Internal frames:
Made of 8X4 pieces: 8 pieces for each of the 4 frames used to make the GEM stack
Sandblasting and polyurethane to prevent dust problems
October 16, 2013
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Current GE1/1 Detectors
GEM foil in inner frame assembly
GEM foil with inner & outer frame
Inside of readout board with O-ring seal
Base pcb with drift electrode
No spacers in active volume
-sector with 384 radial readout strips
October 16, 2013
M. Tytgat - RD51 Collaboration Meeting

15. GE1/1 Readout & Drift Board
vias
Strip side
External side
Readout board: metalized vias bring the signal to the other side of the board; panasonic connector with 128 entries is soldered on the strips
Drift board: HV spring contacts to connect foils to HV; 4 contacts per GEM (Top/Bottom + redundant connection)
HV divider
Soldering spring contacts
HV filter
October 16, 2013
M. Tytgat - RD51 Collaboration Meeting

16. Exploded GE1/1 View Cover Position of HV Divider DC-DC Converters
Cooling
GBT’s
Connectors & FE Hybrids
GE1/1 Triple-GEM Chamber
October 16, 2013
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GE1/1 Cooling System
The cooling system has been studied/simulated taking into account electronics power dissipation (based on VFAT)
The cooling system will ensure a chamber temp. uniformity of (20  1) 0C
44mm
50mm
VFAT
PCB
VFAT power – 600mW
VFAT chip dimensions ~10×10mm
Connectors – 6mm high
3mm PCB
6mm
Cu pipe
1mm Cu strip
VFAT chip
6mm/8mm
at 18o C
VFAT PCB
Panasonic
connectors
Soldered to the pipe
6.5mm
R/o strips
October 16, 2013
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GE1/1 Gain Uniformity
Rate
Gain measured per sector to probe uniformity across surface
HV (V)
October 16, 2013
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19. Detector Simulation Studies
Ongoing simulation effort in several areas:
Standalone simulation of a triple-GEM cell, with GARFIELD and ANSYS or MAXWELL :
Detector gain
Response uniformity (check with X-ray results)
Signal induction and timing studies
Gas gap variations
Background simulations (neutrons & photons) with GEANT4:
GEM sensitivity/response to neutrons and photons
Effect on GEM muon trigger and reconstruction performance
FastSim:
fast GEM simulation parametrized using GARFIELD input
October 16, 2013
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Aging CERN GIF
CMS prototype
A CMS GE1/1 detector was installed in the CERN GIF; detector performance and environmental & gas parameters monitored:
Ensure long-term operation inside CMS
Understand effects of radiation on the materials
Understand ageing origin (if any) and propose solutions
lead shield
CMS high-η GEM
max. integrated charge
Gain of 2x104
50 MHz/cm2 X-rays,
10 days = > 20 C/cm2 integrated
LHCb
GEM settings:
Drift: 3 kV/cm, Others: 3.5 kV/cm Induction: 5 kV/cm
Gain: 8 x 103 – 104; Gas mix: Ar/CO2/CF4 (45:15:40)
October 16, 2013
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21. Possible Assembly Sites
USA
FIT
India
BARC
CERN: 186
CERN
Foil Production and final detector QC
Italy
Bari
LNF
Belgium
Ghent University
Installation in CMS
October 16, 2013
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22. M. Tytgat - RD51 Collaboration Meeting
GE1/1 Quality Control
Final detectors for installation in CMS will undergo strict Quality Control in the different assembly sites:
Measure the leakage current of the GEM foils before, during and after the detector assembly
Validate the readout board by verfiying the connections of the strips to the readout connector
Measuring the detector gain uniformity with Mini-X and SRS/APV system
Response to x-ray checked for each η sector
GE1/1 detector uniformity
October 16, 2013
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23. M. Tytgat - RD51 Collaboration Meeting
Super Chamber Dummies
3 Super Chamber dummies were produced earlier this year to optimize design and to perform trial insertion into CMS:
no detector and no electronics inside
all positions for gas , cooling and electronics connections at the right place
dimensions as a real super chamber
October 16, 2013
M. Tytgat - RD51 Collaboration Meeting

24. Trial Installation in CMS
October 16, 2013
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25. 2014: Final Detector Geometry
Final (?) GE1/1 version should extend as much as possible in |η| :
“long” and “short” super chamber version
Several integration issues to solve
new version
Old version
October 16, 2013
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26. M. Tytgat - RD51 Collaboration Meeting
DAQ and Electronics
Global Requirements on electronics: provide necessary input from all GEM detectors to Muon Triggering and Tracking
GEM detectors:
Design optimized for gas detectors, in particular GEMs
Triggering:
Provide “Fast OR” trigger information with granularity of 2 or more channels to send locally to CSC Trigger Mother Board
Timing resolution <8ns
Tracking:
Provide full granularity tracking data on receipt of a LV1A
Be compatible with CMS trigger upgrade possibilities:
LV1A latency < 20μs
LV1A rate < 1MHz Poisson
October 16, 2013
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DAQ and Electronics
GBT protocol
Or 8b/10b encoding ?
2 Bidir. optical 3.2 Gbps
October 16, 2013
M. Tytgat - RD51 Collaboration Meeting

28. Front-End ASIC Options
VFAT3:
Front-end with programmable shaping time
Internal calibration
Binary memory
Interface directly to 320Mbps
Designed for high rate (10kHz/cm2 depending on segmentation)
GdSP:
Similar to VFAT3, except has an ADC for each channel instead of comparator
Internal DSP allows subtraction of background artifacts, enabling clean signal discrimination
Center of gravity is possible to achieve finer pitch resolution
October 16, 2013
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VFAT3
VFAT3 chosen for GEM Demonstrator and GE1/1 full installation during LS2
VFAT3 analog discriminator will use CFD or TOT to correct time walk
VFAT3 STT version (Separate Tracking & Triggering) : different paths for triggering and full granularity information
October 16, 2013
M. Tytgat - RD51 Collaboration Meeting

30. GEB = GEM Electronics Board M. Tytgat - RD51 Collaboration Meeting
Electronics System
GEB = GEM Electronics Board
GEM OptoHybrid
October 16, 2013
M. Tytgat - RD51 Collaboration Meeting

31. Trigger Concerns for LHC Phase 2
Phase-2 muon Level-1 trigger will rely on tracking trigger and muon candidate matching
But, track trigger fake rate grows with η; maintaining reasonable trigger rate causes severe inefficiencies for |η|>
GE-1/1 is doing exactly what one wants it to do for |η| < 2.1: it compensates for the weakening of the tracker’s suppression power at higher |η| by strengthening the muon system
How do we cover region |η|>2.15 ??
Reco’ed stubs pT>2
Stubs from true particles w/ pT>2
Muon gun pT>5 GeV
Efficiency includes track finding only. No muon system inefficiencies incorporated.
October 16, 2013
M. Tytgat - RD51 Collaboration Meeting

32. Ideas for Phase-2 CMS Muon System
Near tagger ME-0 at the back of present HE with trigger capabilities in |η|>2.1; can be integrated with the calorimeter if desired
GE-1/1 + GE-2/1 GEM stations
RE-3/1 + RE-4/1 gRPC stations ?
LS2
LS3
LS3
October 16, 2013
M. Tytgat - RD51 Collaboration Meeting

33. Extending Muon Coverage
CMS is looking into a possibility to extend tracking to |η|~4.0
Forward pixel extension
A new “Near Tagger”: a large increase in offline acceptance up to |η|=4
ME0:
small area, but nearly doubles CMS muon coverage
Can optionally be integrated into the new forward calorimeter
Match muon stubs and forward pixel extension tracks
Muon system improves momentum resolution
October 16, 2013
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34. M. Tytgat - RD51 Collaboration Meeting
Summary
Over 4 years of R&D initiated in 2009 within the RD51 Collaboration resulted in partial approval for installation of triple-GEM detectors in CMS
During LHC Year-End Technical Stop of (?), two Triple-GEM Super Chambers will be installed in YE1/1
Awaiting further green light from CMS Management for full GE1/1 installation during LS2
Preparing GE1/1 Technical Design Report, ready for October 2014
GEMs are now also being considered as candidate technology for further CMS upgrades during LS3 (ME-0 muon tagger, forward calorimetry)
See also CMS GEM talks in WG6/7 & WG2 sessions by
J. Merlin, P. Barria, A. Zhang, A. Marinov
GE1/1 detector today
@ FNAL test beam
October 16, 2013
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35. M. Tytgat - RD51 Collaboration Meeting
Backup Slides
October 16, 2013
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36. Summary of Effects on Trigger
A second detector with high spatial resolution in station YE-1/1 provides new powerful ways to improve forward muon triggering
Much improved resolution eliminates the famous “rate flattening” problem
A factor of x5-10 reduction in the trigger rate in the region covered by GEMs (1.6<|η|<2.1)
When averaged over (1.1<|η|<2.1), effectively a factor of 2 reduction in muon trigger rate for the entire forward region
Amplified improvement from combining the new handles with the existing ones – a better final trigger system
While critical for the time period between LS2 and LS3, will remain very important beyond LS3 as L1 inner tracking trigger performance likely to be limited beyond |η|=1.8
Installing additional GEM stations (ME-2/1) in LS3 is expected to allow efficient triggering beyond |η|=2.1
October 16, 2013
M. Tytgat - RD51 Collaboration Meeting

37. Effect on Trigger & Physics13 42
Example of where GE1/1 (1.6<|η|<2.1) can help:
Upgraded Muon TrackFinder alone only allows decreasing the threshold from 42 to 25 GeV (with 9% efficiency loss)
Using GEM-CSC “bending angle”, allows to lower pT threshold from 42 to 13 GeV while increasing the efficiency
Hττ μτhad signal: fast falling muon momentum spectrum requires low pT thresholds; loose half (!) of the acceptance every time pT threshold by 10 GeV
GEM+CSC yield improved background rejection and result in ~20% increase in acceptance
no L1 upgrade
GEM+CSC
L1 upgrade
October 16, 2013
M. Tytgat - RD51 Collaboration Meeting

38. Muon detectors in new endcap
At back of present HE
Totally new calorimeter
Existing structure too “hot”
Coverage options:
Minimal (top), maximal (bottom) shown on right
{1.5, 2.1, 2.4} < |h| < {3.5, 4.0}
Complement or replace ME1/1
“Integrated” option
Build all of HE with GEM technology, for example m
new HE m
October 16, 2013
M. Tytgat - RD51 Collaboration Meeting