Abstract Beam Test of a Large-area GEM Detector Prototype for the Upgrade of the CMS Muon Endcap System V. Bhopatkar, M. Hohlmann, M. Phipps, J. Twigger, A. Zhang Dept. of Physics and Space Sciences, Florida Institute of Technology, Melbourne, FL 32901, USA ( for the CMS GEM Collaboration)Motivation Gas Electron Multiplier (GEM) technology is being considered for the forward muon upgrade of the CMS experiment in Phase 2 of the CERN LHC. The first such implementation is planned for the GE1/1 system in the 1.5<|η|<2.2 region of the muon endcap. With precise tracking and fast trigger information, this system can significantly improve the CMS muon trigger as shown previously in simulations. We assembled a 1m full-size prototype of a GE1/1 triple-GEM detector with 3,072 radial readout strips at Florida Tech and tested it in hadron beams at Fermilab in October Strip cluster parameters, detection efficiency, and spatial resolution for charged particles are studied with position and high voltage scans and at different inclination angles. Strip cluster sizes increase with high voltage. We find a plateau detection efficiency of (97.8 ± 0.2)%. All eight eta sectors of the prototype detector show similar high efficiencies. Results of response uniformity and spatial resolution studies using four GEM-based reference tracking detectors are presented. Preliminary results show a spatial resolution of 97 µrad or 21% of strip pitch.  Florida Tech is planning to contribute to this upgrade project by producing approximately 40 detectors. We constructed a first large-area GEM detector and studied its characteristics at a test beam at Fermilab in Oct Construction of GE1/1 Prototype III Large-Area GEM Detector (at Florida Tech) Step III: Finished GEM detector w/ APV frontend hybrids connected Strip Pitch 1.05mm Strip Pitch 0.67mm Length 1m 3mm 1mm 2mm 1mm Drift electrode GEM 1 GEM 2 GEM 3 Anode (readout)  1D readout board with 3,072 radial strips connected through 24 Panasonic connectors to 24 APV hybrids Internal gap configuration of the detector: 3/1/2/1mm  GEM foils produced by single mask etching technique at CERN  Active area: approximately 99×(28-45)cm 2 FNAL Test Beam Oct Setup and Measurements Trackers CMS GE1/1-III Detector  Gas mixture used in all detectors: Ar/CO 2 70:30  Beam Energies: 32 GeV mixed hadrons;120 GeV p  4 GEM 4200V  DAQ with RD51 SRS  CMS detector tests: 1. High voltage scan from 2900V to 3300V 2. Position Scan at 3250V in 3 positions: Upper row APV Middle row APV Lower row APV Performance Characteristics from FNAL Test Beam Data Reference Tracker and Correlations with CMS GE1/1 Detector Detection Efficiency is 97.8%  During the phase II upgrade process, we are planning to install large-area GEM detectors in the forward muon region.  GEM technology will improve overall muon trigger efficiency by providing fast triggering and precise tracking information. Step I: GEM foils assembly with inner frames Step II: Stretching GEM foils by providing tension Stretched GEM foils with inner and outer frames Cluster Charge Distribution Cluster charge distribution fitted with Landau function at 3250V Cluster Size at 3250V Cluster size increases with voltage Cluster Size vs. High Voltage Beam profiles Preliminary Tracking Results for CMS GE1/1-III Tracking is done in three steps:  Step I - Alignment: By iterating the shift parameters in X and Y, we center all detector residuals on zero and then with respect to the first reference tracker, we rotate the remaining three trackers until the residual widths are minimized.  Step II - Conversion from (x,y) to (r,φ) coordinate system: Since we are dealing with radial readout strips in the GE1/1, it is more appropriate to use (r,φ) coordinates for tracking.  Step III - Calculate final residuals (inclusive and exclusive) At 3250V  At 3250V, most probable values for all 3 APV position are used to determine the charge uniformity across the detector:  Detection efficiency measured with this detector is 97.8% (with 5-sigma cut on pedestal width).  Average cluster size at operating voltage is 2.3 strips Detection Efficiency with Different Cuts on Pedestal Widths Correlation of GE1/1 detector hits with hits in first tracking detector:  This translates to residual widths of σ = 201 µm (exclusive) and σ = 160 µm (inclusive) in the azimuthal direction (at the center of the eta sector 5) using R=1850 mm.  Taking the geometric mean of exclusive and inclusive residual widths we find a resolution of σ = 97µrad (21% of strip pitch) which corresponds to σ = 179 µm in the center of eta sector 5 when using the pulse-height sensitive analog readout.  Conclusion: The performance of this GE1/1 prototype in a beam meets expectations. Charge Uniformity Inclusive Residual in Eta 5 SectorExclusive Residual in Eta 5 Sector CMS Upgrade week, Karlsruhe (Germany) - April 2014 Inclusive σ = 21µrad 32 GeV mixed-hadron 120 GeV proton Exclusive σ = 75µrad Reference detector resolutions in φ Preliminary σ= 87 µrad in φ Preliminary σ= 109 µrad in φ Tracker 1 Tracker 2 Tracker 3Tracker 4 Residuals of Tracker 1