A GEM Detector System for an Upgrade of the CMS Muon Endcaps

25 Results obtained with GE1/1-I during the Oct. 2010 test beam campaign: (a) residual distribution;
(b) detector hit efficiency as function of the current in the HV divider, which is proportional to the
electric fields in the GEM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
26 GE1/1-II performance: cluster size (left) and space resolution (right) at high and low η measured
with VFAT2 binary electronics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
27 GE1/1-II efficiency performance at high and low η ends. Efficiency reaches 96.5% at gain 7000. . 30
28 Results for GE1/1-II using pulse height measurements with APV25/SRS during the Aug. 2011
test beam campaign: (a) strip cluster size distribution; (b) difference ∆x between hit positions
measured with GE1/1-II and with a reference GEM in the tracker. . . . . . . . . . . . . . . . . . 30
29 Left: ∆y distribution forTR5 andTR1. Right: ∆x distribution for TR5 and GE1/1-II using central
tracks in a pion beam. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
30 Left: GE1/1-II cluster sizes inside a strong magnetic field. Right: Comparison of measured and
simulated strip cluster position displacement in GE1/1-II due to an external magnetic field. . . . . 31
31 The self-stretching Triple-GEM assembly technique: (a) GEM foil before assembly; (b) external
frame for foil stretching; (c) mounting the GEM foils; (d) stretching the foils; (e) stretched GEM;
(f) completed detector including readout board. . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
32 Gain curve of the 30 cm × 30 cm self-stretched GEM prototype detector. . . . . . . . . . . . . . 33
33 The electric field as seen in Garfield at the center of the GEM . . . . . . . . . . . . . . . . . . . . 35
34 Exploded view of a Triple-GEM arrangement (Distances are not to scale) . . . . . . . . . . . . . 36
35 Diffusion coefficient for two different gas mixtures under study in presence of magnetic field and
with angle θ(E,B) = 8 ◦ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
36 Diffusion coefficients for magnetic fields = 0T and 3T withθ(E,B) = 90 ◦ . . . . . . . . . . . . . 37
37 Lorentz angles for the gas mixtureAr/CO2/CF4 for the anglesθ(E,B) = 8 ◦ (left) andθ(E,B) =
90 ◦ (right) for a magnetic field of 3 T. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
38 The drift velocities for various gas mixtures from simulation and the experimental values from
LHCb studies. The simulation shows a good agreement with the experimental results . . . . . . . 38
39 Loss rate for primary electrons for rp = 0.6. The losses occur due to attachment to the quencher
gas molecules (left) and due to the electrons hitting the surface of copper metal or polyimide walls
(right) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
40 Loss rate for secondary electrons. The losses occur due to attachment to the quencher gas molecules
(left) and due to the electrons hitting the surface of copper metal or polyimide (right) . . . . . . . 40
41 Overall Loss rate for primary (left) and secondary (right) electrons for penning parameter rp = 0.6 40
42 Effective gain (Geff ) and the total gain (Gtot) for different penning parameters. . . . . . . . . . . 41
43 Effective gain comparison for Ar/CO2/CF4 and Ar/CO2 for penning parameter of 0.6 . . . . . 41
44 Triple-GEM effective gain compared with data . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
45 Time resolution for single electrons in the case of Ar/CO2/CF4 (left) and Ar/CO2 (right) . . . . 42
46 Longitudinal view of the current RPC trigger towers in one quadrant of the CMS detector. Chambers
in areas marked with green (RE1/1, RE2/1) were modified to have increased number of strips
to simulate the use of GE1/1 and GE2/1 GEM stations in those locations. . . . . . . . . . . . . . 44
47 Simulated L1 GEM+RPC trigger output rates summed over trigger towers -16 to -13 and 13 to 16
vs. pT cut for ideal chamber model (top left: base, top right: 2×, bottom left: 4×, bottom right:
8× strip granularity). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
48 Simulated L1 GEM+RPC trigger output rates summed over trigger towers -16 to -13 and 13 to 16
vs.pT cut for realistic chamber model (top left: base, top right: 2×, bottom left: 4×, bottom right:
8× strip granularity). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5