Measurement of cosmic-ray muon flux in the underground laboratory at UCIL, India, using plastic scintillators and SiPM

A measurement of cosmic muon flux, in the newly established underground laboratory at the Uranium Corporation of India Limited (UCIL), Jaduguda, Jharkhand, India, has been carried out. Several future low background experiments are planned in this laboratory. The experimental set up for muon flux measurements consists of four plastic scintillators, with three of these coupled to photomultiplier tubes (PMT) to generate a coincidence trigger for acquiring data. The fourth scintillator has been coupled to a Silicon Photomultiplier (SiPM) whose signals were processed with respect to the coincidence trigger. In this scintillator, a mean light yield of 22 photoelectrons per muon event was observed and the measured time resolution was 1.3 ns. The muon flux measurement at the underground laboratory at 555 m ($1554\pm 45$ m w.e.) depth level was $(2.79\pm 0.13\left(stat\right)\pm .20\left(syst\right))\times 10^{-7}c{m}^{-2}se{c}^{-1}s{r}^{-1}$. This agrees well with model predictions. This paper describes the detector system, analysis techniques, and results of measurement at the surface and the underground laboratory.