Simulation of HFO-1234ze(E) - based mixtures in resistive plate chambers

The recent availability of a consistent electron collision cross-section set for the ultra-low GWP HFO-1234ze(E) (HFO) enables performance simulations of resistive plate chambers (RPCs) operated with HFO-based gas mixtures. We present a simulation framework that reproduces key detector observables measured in trigger-purpose RPCs, such as detection efficiency and cluster size. The simulation additionally provides new insights into streamer formation through a novel streamer inception criterion that captures the observed trends in streamer probability. For mixtures containing CO 2 , HFO, SF 6 , and isobutane, the Pareto front between avalanche-streamer separation and relative CO 2 equivalent emissions is evaluated using a multi-objective Bayesian optimization approach under a low working point constraint, so the mixture can be used with already installed infrastructure. The optimization confirms that the ECO2 gas mixture (60 % CO 2 , 35 % HFO, 4 % isobutane, 1 % SF 6 ), previously identified through experimental studies, is a Pareto optimal choice when the operation is constrained to a low working point. If higher working points are acceptable, mixtures with a higher HFO percentage provide larger avalanche-streamer separation while enabling a reduction of the SF 6 percentage, thereby reducing the environmental impact even further.