1. (On Behalf of CMS Muon Group)
Quality Control and Production Status of Large-area GEM Detectors for the CMS Muon Endcap Upgrade
Mehdi Rahmani
Dept. of Aerospace, Physics and Space Sciences,
Florida Institute of Technology
(On Behalf of CMS Muon Group)

2. Outline Introduction Detector Construction & Quality Control (QC)
What is a GEM Detector?
Why GEM Detectors for CMS?
Detector Construction & Quality Control (QC)
Construction of GE1/1 Prototypes for Large-Area GEM Detector
Layout - Cleanroom
QC2: GEM Foil Testing
QC3: Gas Leak Test
QC4: High Voltage Test
QC5: Gain Measurements
Gain Calibration
Response Uniformity
Effective Gain Analysis Across the sites
Outlook

3. What is a GEM Detector?
Kapton foil coated with copper on both sides that has an array of microscopic holes
Inserted between a drift and a charge collection electrode
HHV creates high E-field in GEM holes
Ionizing collisions with the gas molecules filling the structure creating an avalanche of electron-ion pairs

4. What is a GEM Detector?
Kapton foil coated with copper on both sides that has an array of microscopic holes
Inserted between a drift and a charge collection electrode
HV creates high E-field in GEM holes
Ionizing collisions with the gas molecules filling the structure creating an avalanche of electron-ion pairs V

5. Why GEM Detectors for CMS
High-Luminosity LHC
CMS group will install large-area GEM detectors in the forward muon region
Help to restore redundancy for tracking and triggering in muon system
The combination of GEM+CSC
Provides accurate measurement of the muon bending angle unaffected by multiple
Scattering
Can be used in the L1 muon trigger to reduce the soft muon rate

6. Why GEM Detectors for CMS
High-Luminosity LHC
CMS group will install large-area GEM detectors in the forward muon region
Help to restore redundancy for tracking and triggering in muon system
The combination of GEM+CSC
Provides accurate measurement of the muon bending angle unaffected by multiple scattering
Reduces L1 muon trigger rate due to soft muons
View from the top of CMS down

7. Construction Steps a. Mounting inner frames
b. Assembling three GEM foils
c. GEM stack on the drift
d. Stretching foils with tension
e. Stretched foils in frames
f. Mounting readout board

8. Example Assembly & QC Site Layout (FIT)
Cleanroom
Flow of work
DAQ rack
(SRS, HV)
Detector
storage
Outside
hospital
GEM stack
assembly
QC4
Material
receiving
General
work
benches
Inside
hospital
QC2
(slow)*
QC2
(fast)
Chamber
assembly
& QC3
workflow
dashboard
QC5
X-ray box

9. QC Step 2 : GEM Foil acceptance
Fast test
Applying 550 V to the GEM foils and measuring the leakage current between top and bottom electrodes
The GEM foil is accepted if its impedance is above 10 GΩ, with relative humidity lower than 40% and the number of sparks per minutes is lower than 2/3 during the last three minute

10. QC Step 3: Gas Leak Test
After pressurizing the chamber to 25mbar, the pressure drop should not exceed 6 mbar per hour.
Data Taken By Student

11. QC Step 4: High Voltage Test
Aims to determine the V vs. I curve for HV divider
Identify possible malfunctions and defects in the HV circuit
Look for any spurious pulses
Detector under CO2
Ionizing particles can not ionize the CO2 as much
We expect no signals.
FIT0008
Data Taken By Student

12. QC Step 4: High Voltage Test
Aims to determine the V vs. I curve for the HV divider
Identify possible malfunctions and defects in the HV circuit
Look for any spurious pulses
Detector under CO2
Ionizing particles can not ionize the CO2 as much
We expect no signals
FIT0008
Data Taken By Student

13. QC Step 5a: Effective Gain
FIT0009
Measure the gain vs. current in HV divider (prop. to applied voltage) using X-ray source
The gas gain is measured via the anode current produced in the chamber during this irradiation
Data Taken By Student
Typical effective gain curve obtained during the GE1/1 quality control. Idivider is the pressure and temperature corrected current flowing through the HV resistive divider that provides potential to the detector electrodes

14. QC Step 5b: Gain Uniformity
FIT0003
The response uniformity is performed at a gas gain of ≈ 600 using Ar/CO2 (70:30)
Given the large area of the CMS GEM chambers, the uniformity of the detector response across the surface should be assured.
A basic quantity to verify that is the pulse height across the detector.
Work in progress

15. Site model & Achievements
DISTRIBUTED PRODUCTION MODEL
PRODUCTION SUMMARY
Chambers for the first endcap (36 Super Chambers) are ready & qualified.
Installation of the first endcap expected by July 2019.
Production for the second endcap is ongoing.
Total chamber assembly progress
India
USA
(FIT)
CERN
Central
site
Italy
PAK
Total chamber validation progress.
Belgium/Germany
LHCP5
09/04/2019

16. Gain Comparison Analysis
Work in progress

17. Outlook
GE1/1 Installation for the first endcap is foreseen to take place in July 2019.
Second endcap is going to be equipped with the GE1/1 detectors in early 2020.
After second long shut down GE2/1 will be installed.
Will begin operating GE1/1 in LHC Run 3 starting in 2021.

18. Thank you!