Status of the CMS GEM Project

Michael Tytgat on behalf of the CMS GEM Collaboration

RD51 Collaboration Meeting, October 16, 2013

Outline

IntroductionCMS Muon Trigger motivationDetector construction and testsProduction quality control Integration into CMSDAQ and ElectronicsTowards LS3

October 16, 2013

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LS2

LS3

The CMS GEM Project

GE1/1

Install triple-GEM super chambers (double stations) in 1.6<|η|<2.1-2.4 endcap region:

GE2/1

• 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

GEMs: R&D Project CMS 10.02; The LS2 ProjectOctober 16, 2013

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OVER FOUR YEARS OF R&D • 2009-2010

– 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

Project Milestones

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2012• Beam tests – Magnetic Field Operation and fine space and time resolution on

large size establishedWorking 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

Project Milestones

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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

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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

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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

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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

View from the top of CMS down

October 16, 2013

GEM-CSC “Bending Angle”

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Detector Hardware

2010

Generation IThe first 1m-class detector ever built but still with spacer ribs and only 8 sectors total. Ref.: 2010 IEEE (also RD51-Note-2010-005)

2011 2012 2013

Generation IIFirst 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-2011-013.

Generation IIIThe first self-stretched sans-spacer detector, but with the outer frame still glued to the drift. Ref.: 2012 IEEE N14-137.

Generation IVThe 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 2013and IEEE2013.

2013/14

Generation VThe upcoming detector version that we will install. One long and one short version. Optimized final dimensions for max. acceptance and final eta segmentation.

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Full-size GE1/1 Detectors Developments in Time

2010 2011 2012 2013 2013/14

2014/15 2015/16 2016/17 2017/18 2018/19

Production and QC of detectorsFirst prototype of VFAT3

Slice installation

Slice and trigger commissioning

Full-production of chambers and electronics started

Full installation of GE1/1 with final electronics

QC of Production GE1/1 chambers with final electronics

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Current GE1/1 Detectors

October 16, 2013

Single-mask & self-stretching techniques Gap sizes: 3/1/2/1 mm Sectors : 3 columns x (8-10) η partitions Strip pitch: 0.6-1.2mm 1D readout of up to 3840 channels 35 HV sectors

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NS2 Self-Stretching Technique

October 16, 2013

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

Detector Frames

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GEM foil in inner frame assembly GEM foil with inner & outer frame

Inside of readout board with O-ring seal

-sector with 384 radial readout strips

Base pcb with drift electrode

No spacers in active volume

Current GE1/1 Detectors

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Strip side External side

vias

Readout board: metalized vias bring the signal to the other side of the board; panasonic connector with 128 entries is soldered on the stripsDrift board: HV spring contacts to connect foils to HV; 4 contacts per GEM (Top/Bottom + redundant connection)

GE1/1 Readout & Drift Board

HV filter

HV divider

Soldering spring

contacts

Cover

Connectors & FE Hybrids

Exploded GE1/1 View

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Cooling

GE1/1 Triple-GEM Chamber

Position of HV Divider

GBT’s

DC-DC Converte

rs

GE1/1 Cooling System

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VFAT power – 600mWVFAT chip dimensions ~10×10mmConnectors – 6mm high

44mm50

mmVFAT

PCB

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

3mm PCB

6mmCu

pipe

1mm Cu strip

VFAT chipCu pipe

6mm/8mmat 18o C

VFAT PCB

Panasonicconnectors

Soldered to the pipe

6.5mm

R/o strips

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2700 2900 3100 3300 3500 3700 39000

2

4

6

8

10

12

HV (V)

Rate

GE1/1 Gain Uniformity

October 16, 2013

Gain measured per sector to probe uniformity across surface

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Detector Simulation Studies

October 16, 2013

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

Aging test @ CERN GIF

20

lead

shi

eld

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

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)

CMS high-η GEM

max. integrated

chargeGain of 2x104

50 MHz/cm2 X-rays, 10 days = > 20 C/cm2 integrated

CMS prototype

October 16, 2013 M. Tytgat - RD51 Collaboration Meeting

LHCb

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CERNFoil Production

and final detector QC

USA FIT

ItalyBariLNF

IndiaBARC

BelgiumGhent

University

Installation in CMS

CERN: 186

October 16, 2013

Possible Assembly Sites

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GE1/1 Quality Control

October 16, 2013

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

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Super Chamber Dummies3 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

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Trial Installation in CMS

October 16, 2013

2014: Final Detector Geometry

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Final (?) GE1/1 version should extend as much as possible in |η| : 1.5-2.2

“long” and “short” super chamber versionSeveral integration issues to solve

Old version

new version

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DAQ and Electronics

October 16, 2013

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

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GBT protocolOr 8b/10b encoding ?

2 Bidir. optical link @ 3.2 Gbps

DAQ and Electronics

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Front-End ASIC Options

October 16, 2013

VFAT3:

Front-end with programmable shaping time

Internal calibration Binary memory Interface directly to GBT @

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

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VFAT3

October 16, 2013

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

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Electronics System

October 16, 2013

GEM OptoHybrid

GEB = GEM Electronics

Board

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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|>1.8-2.0 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 ??

Muon gun pT>5 GeVEfficiency includes track finding only. No muon system inefficiencies

incorporated.

Reco’ed stubs pT>2Stubs from true particles w/ pT>2

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Ideas for Phase-2 CMS Muon System

LS2

LS3LS3

October 16, 2013

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 ?

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Extending Muon Coverage

CMS is looking into a possibility to extend tracking to |η|~4.0o Forward pixel extension

A new “Near Tagger”: a large increase in offline acceptance up to |η|=4

ME0: o small area, but nearly doubles

CMS muon coverageo Can optionally be integrated

into the new forward calorimeter

o Match muon stubs and forward pixel extension tracks

o Muon system improves momentum resolution

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Summary

October 16, 2013

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 2015-2016 (?), 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

Backup Slides

October 16, 2013

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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

Summary of Effects on Trigger

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Effect on Trigger & PhysicsExample 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

Hττ 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

13

42

L1 upgrade

no L1 upgrade

GEM+CSC

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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

new HE

m

m

October 16, 2013