Radiation Tests of Real-Sized Prototype RPCs for the Future CMS RPC Upscope

TL;DR

This study systematically evaluates the performance of double-gap and four-gap phenolic RPCs for future CMS high-{ exteta} triggers, demonstrating their high rate capabilities and effective suppression of muon hit cluster sizes under gamma irradiation.

Contribution

It provides the first comprehensive comparison of double-gap and four-gap RPCs' rate capabilities and threshold behaviors under gamma irradiation for future high-{ exteta} trigger applications.

Findings

Four-gap RPCs have lower gamma-induced currents than double-gap RPCs.

Both RPC types exceed the rate requirements for future high-{ exteta} LHC triggers.

High thresholds in four-gap RPCs suppress muon hit cluster size increases.

Abstract

We report on a systematic study of double-gap and four-gap phenolic resistive plate chambers (RPCs) for future high-{\eta} RPC triggers in the CMS. In the present study, we constructed real-sized double-gap and four-gap RPCs with gap thicknesses of 1.6 and 0.8 mm, respectively, with 2-mm-thick phenolic high-pressure-laminated (HPL) plates. We examined the prototype RPCs for cosmic rays and 100 GeV muons provided by the SPS H4 beam line at CERN. We applied maximum gamma rates of 1.5 kHz cm-2 provided by 137Cs sources at Korea University and the GIF++ irradiation facility installed at the SPS H4 beam line to examine the rate capabilities of the prototype RPCs. In contrast to the case of the four-gap RPCs, we found the relatively high threshold was conducive to effectively suppressing the rapid increase of strip cluster sizes of muon hits with high voltage, especially when measuring the narrow-pitch strips. The gamma-induced currents drawn in the four-gap RPC were about one-fourth of those drawn in the double-gap RPC. The rate capabilities of both RPC types, proven through the present testing using gamma-ray sources, far exceeded the maximum rate expected in the new high-{\eta} endcap RPCs planned for future phase-II LHC runs.