Improving time and position resolutions of RPC detectors using time over threshold information

Abstract

INO-ICAL is a proposed underground experiment to study the oscillation parameters of neutrinos by detecting those produced in the atmospheric air showers. The Iron CALorimeter (ICAL) is to have 151 layers of iron plates stacked vertically corresponding to a height of ∼14.5 m, with active detector elements inserted between the iron layers. The iron layers will be magnetized with a maximum magnetic field of 1.5 T to enable the measurement of the charge and momentum of the μ - (or μ +) produced by ν μ (or ν̅ μ ) interactions inside the detector throughout the operation. Resistive Plate Chambers (RPCs) have been chosen as the active detector elements as they are amenable to large area coverage, as well as due to their high particle detection efficiency, long-term performance and low cost of production. The major factors that weigh in on the physics potential of the ICAL detector are the efficiency, position resolution and time resolution of the large area RPCs. A prototype detector called mini-ICAL (with 11 iron layers) was commissioned in order to understand the engineering challenges in building the large-scale electromagnet and its ancillary systems, and also to study the performance of the RPC detectors and readout electronics developed by the INO collaboration. As part of the performance study of the RPC detectors, an attempt is made to improve their position and time resolutions. The designed position resolution for the ICAL detector is of the order of 1 cm and the required time resolution is ∼1 ns. Even a small improvement in the position and time resolution will help to improve the measurements of momentum and directionality of the neutrinos in the ICAL detector. In ICAL detector simulation, where muons traverse in all directions with on average 20 RPC layers, a 30 % improvement in position resolution results in ∼10 % improvement in the momentum resolution at 3 GeV. Due to large iron materials in between two RPCs, the resolution is dominated by the effect of multiple scattering at this momentum. Also for a muon with 10 layer hit, the charge ambiguity reduces from 0.04 % to 0.001 % when the time resolution improves from 1 ns to 0.7 ns. The Time-over-Threshold (ToT) of the RPC pulses is recorded by the readout electronics. ToT is a measure of the pulse width and consequently the pulse amplitude. This information is used to improve the time and position resolution of RPCs and consequently INO's physics potential.

Fine tuning of gas system and performance studies of RPC detectors in the INO's mini-ICAL detector

“…The progressive increase in noise rate and multiplicity represents a constant increase in the amount of induced signals in the RPC detector, influencing efficiency characteristics. The efficiency of the RPC is determined by measuring the ratio of the number of events recorded by the RPC to the number of fired events generated by the trigger RPCs [9]. During this study, the trigger criteria for the mini-ICAL detector were Layer 9, 8, 7, and 6 F&B RPCs (the top four layers of both front and rear RPCs in the detector stack are the trigger RPCs).…”

Simulation of RPC responses in mini-Iron Calorimeter for cosmic ray muon studies

“…Once the trigger is formed the digitized data is transmitted to the back-end using the DAQ boards network interface [6]. More detail on this setup is available in [3]. For the last four decades, RPCs have been used in high-energy physics experiments.…”

“…As is seen in figure 3(a) there are 2-3 hits due to muon trajectory, which is common in the RPC detector. For a good position resolution, a hit multiplicity of more than three is avoided [3]. In the presence of noise in a layer, there are possibilities that other hits might be visible in some other strips far away from the muon trajectory.…”

“…The alignment of the readout panels of the RPCs was performed offline using the methodology outlined in the work by S. Pal et al [11]. The time offset alignment procedure is detailed in the study conducted by [3]. It is essential to accurately incorporate the misalignment in the simulation, as it notably impacts the azimuthal and zenith angle distributions.…”