Tests of multigap RPCs for high-η triggers in CMS

Abstract

In this paper, we report a systematic study of multigap Resistive Plate Chambers(RPCs) for high-η triggers in CMS. Prototype RPC modules with four- and six-gap structureshave been constructed with phenolic high-pressure-laminated (HPL) plates and tested withcosmic muons and gamma rays irradiated from a 200-mCi 137Cs source. The detectorcharacteristics of the prototype multigap RPCs were compared with those of the double-gapRPCs currently used in the CMS experiment at LHC. The mean values for detector charges ofcosmic-muon signals drawn in the four- and six-gap RPCs for the efficiency values in themiddle of the plateau were about 1.5 and 0.9 pC, respectively, when digitized with chargethresholds of 150 and 100 fC, respectively. They were respectively about one third and one fifthof that drawn in the current CMS double-gap RPC with a charge threshold of 200 fC. Weconcluded from the current R&D that use of the current phenolic-HPL multigap RPCs isadvantageous to the high-η triggers in CMS in virtue of the smaller detector pulses.