CERN Accelerating science

ATLAS Note
Report number	ATL-MUON-PROC-2024-018
Title	Performance of the ATLAS RPC detector and Level-1 muon barrel trigger with a new $\mathrm{CO_2}$-based gas mixture
Author(s)	Su, Shixiang (University of Science and Technology of China (CN))
Corporate Author(s)	The ATLAS collaboration
Collaboration	ATLAS Collaboration
Publication	2024
Imprint	09 Dec 2024
Number of pages	8
Subject category	Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN LHC ; ATLAS
Free keywords	RPC performance ; new CO2-based gas mixture ; HV correction
Abstract	Resistive Plate Chambers (RPCs) are used in the ATLAS experiment for trigger on muons in the barrel region. The current RPC detectors operate with a Freon-based gas mixture containing $\mathrm{C_2H_2F_4}$ and $\mathrm{SF_{6}}$, both of which have a high global warming potential. To reduce environmental impact and operating costs, it is essential to explore alternative, environmentally friendly gas mixtures. In August 2023, after the completion of proton-proton data-taking, the ATLAS collaboration replaced the standard gas mixture (94.7% $\mathrm{C_2H_2F_4}$, 5.0% $\mathrm{i\mbox{-}C_4H_{10}}$, 0.3% $\mathrm{SF_6}$) with a new mixture with $\mathrm{CO_2}$ added: 64% $\mathrm{C_2H_2F_4}$, 30% $\mathrm{CO_2}$, 5.0% $\mathrm{i\mbox{-}C_4H_{10}}$, 1% $\mathrm{SF_6}$. This paper presents the performance of the RPC detector with the new mixture, focusing on detector current density, cluster size, and the efficiency of the Level-1 muon barrel trigger system.