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

Figure 42: Effective gain (Geff ) and the total gain (Gtot) for different penning parameters.
A comparison of the effective gain with Ar/CO2 can be seen in Fig. 43 for one penning parameter rP = 0.6. As
can be seen, the effective gain reduces considerably in the case of Ar/CO2 by a factor of 1/2. However, we are
using Ar/CO2/CF4 because CF4 being a fast gas gives fast response and an improved time resolution. The time
resolution obtained in the case of Ar/CO2/CF4 and Ar/CO2 can be seen in Fig. 45. The average time in case
of Ar/CO2/CF4 is 23 ns with a resolution of 0.5 ns while for Ar/CO2, it is 33 ns with a resolution of 1.2 ns.
However, the figures in 45 do not show a realistic time resolution because we have not done a primary particle
ionization simulation and it just shows the effect of usingCF4 gas.
Figure 43: Effective gain comparison for Ar/CO2/CF4 and Ar/CO2 for penning parameter of 0.6
In order to study the Triple-GEM, we simulate three single GEMs and the overall gain Gtgem, is defined as :
Gtgem = G1 ∗G2 ∗G3
, where G1, G2 and G3 are the single GEM gains. The Triple-GEM results compared with the gain obtained
in GE1/1 prototype II of CMS is seen in the Fig. 44 for the different penning parameters. As can be seen, for a
penning parameter ofrP = 0.6, a good agreement is obtained for the different overall potentials of the Triple-GEM
configuration as compared to data.
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