Charge-dependent atmospheric muon flux at 17 GV geomagnetic cutoff measured with the mini-ICAL prototype

Abstract

The Iron CALorimeter (ICAL) detector at the India-Based Neutrino Observatory (INO) was conceived as an underground experiment designed to measure atmospheric neutrino oscillation parameters. As part of the R\&D programme, a scaled prototype (mini-ICAL), 85\,ton, approximately 1/600$^{\mathrm{th}}$ the mass of the full detector, was constructed at the IICHEP Transit Campus, Madurai (altitude 150\,m; latitude 9.9372$^\circ$\,N; longitude 78.013$^\circ$\,E; geomagnetic latitude 1.44$^\circ$\,N; vertical cutoff rigidity 17\,GV) and operated between 2018 and 2022. The prototype enabled measurements of charge-dependent cosmic muon spectra in the vicinity of the geomagnetic equator and provided an important validation of detector performance, reconstruction algorithms, and simulation frameworks for the ICAL experiment. Differential fluxes of $μ^{-}$ and $μ^{+}$ were measured over the momentum range $\sim$\,1--5\,GeV/c. The obtained momentum spectra are systematically lower than those reported at sites with smaller geomagnetic cutoff rigidities, consistent with the suppression of low- and intermediate-rigidity primary cosmic rays at the 17\,GV cutoff. The measurements are compared with predictions from different hadronic interaction models available in CORSIKA simulations.