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

Abstract: A Prototype of the Iron Calorimeter for the India-based Neutrino Observatory is currently running in Madurai, India. This consists of twenty large area single gap Resistive Plate Chambers (RPCs) of size, $\sim$ 185\,cm $\times$ 175\,cm sandwiched between 11 layers of iron plates of thickness 5.6\,cm. The total size of the mini-Iron Calorimeter(mini-ICAL) is 4\,m$\times$4\,m$\times$1.2\,m and having a weight of 85\,tons is a (1/600) scaled-down version of the ICAL detector of INO~\cite{ichep2018}. The detector is magnetized using iron plates and two sets of copper coils, each coil has 18 turns. The central region of the mini-ICAL, where the RPCs are placed, has a nearly uniform magnetic field of 1.4\,T, similar to the magnetic field in the final ICAL detector. This prototype serves as the basis for the design of the demonstrators, which closely mimics the characteristics of a future ICAL. This detector is built to test the final electronics in the fringe field of the magnet and also to develop the experience to construct the ICAL detector. The mini-ICAL has been operational since 2018 and collects cosmic muon data with different configurations of RPC, and electronics, which are continuously changing for various R&D efforts. Dedicated efforts are made in parallel to measure the momentum and azimuthal angle of $\mu^+$ and $\mu^-$ independently, which could be an important input to the cosmic neutrino event generators. To improve the precision of those measurements a dedicated simulation effort was made, particularly in the digitisation of the RPC signal for a real detector simulation, where efficiency, noise rate, strip multiplicity, etc. were matched with the real data collected during runs at mini-ICAL.