The phenomenon of neutrino oscillation is now well understood from the solar, atmospheric, reactor and accelerator neutrino experiments. This oscillation is characterized by a unitary PMNS matrix which is parametrized by three mixing angles (𝜃₁₂, 𝜃₂₃ and 𝜃₁₃) and one phase (𝛿_CP) known as the leptonic CP phase. Neutrino oscillation also involves two mass squared differences: the solar mass square difference (𝛥₂₁ = 𝑚₂² − 𝑚²₁) and the atmospheric mass square difference (𝛥₃₁ = |𝑚²₃−𝑚²₁|). Though there is already significant amount of information about the three mixing angles, the CP phase is still unknown. Apart from the CP phase, one should also know what is the true nature of the neutrino mass hierarchy, i.e., normal (𝑚₃ > 𝑚₁: NH) or inverted (𝑚₁ > 𝑚₃: IH) and what is the true octant of 𝜃₂₃, i.e., lower (𝜃₂₃ < 45°: LO) or higher (𝜃₂₃ > 45°: HO). The long-baseline experiments (LBL) have CP sensitivity coming from the appearance channel $(\nu_{\mu} \rightarrow \nu_{e}$). On the other hand, atmospheric neutrinos are known to have negligible CP sensitivity. In this work, we study the synergy between the LBL experiment NO𝜈A, T2K and the atmospheric neutrino experiment ICAL@INO for obtaining the first hint of CP violation in the lepton sector. We find that due to the lack of knowledge of hierarchy and octant, CP sensitivity of NO𝜈A/T2K is poorer for some parameter ranges. Addition of ICAL data to T2K and NO𝜈A can exclude these spurious wrong-hierarchy and/or wrong-octant solutions and cause a significant increase in the range of 𝛿_CP values for which a hint of CP violation can be achieved. Similarly, the precision with which 𝛿_CP can be measured also improves with the inclusion of ICAL data.

The upcoming 50 kt magnetized iron calorimeter (ICAL) detector at the India-based Neutrino Observatory (INO) is designed to study the atmospheric neutrinos and antineutrinos separately over a wide range of energies andpath lengths. The primary focus of this experiment is to explore the Earth matter effects by observing the energy and zenith angle dependence of the atmospheric neutrinos in the multi-GeV range. This study will be crucial toaddress some of the outstanding issues in neutrino oscillation physics, including the fundamental issue of neutrino mass hierarchy. In this document, we present the physics potential of the detector as obtained from realistic detector simulations.We describe the simulation framework, the neutrino interactions in the detector, and the expected responseof the detector to particles traversing it. The ICAL detector can determine the energy and direction of the muons to a high precision, and in addition, its sensitivity to multi-GeV hadrons increases its physics reach substantially. Itscharge identification capability, and hence its ability to distinguish neutrinos from antineutrinos, makes it an efficient detector for determining the neutrino mass hierarchy. In this report, we outline the analyses carried out for the determination of neutrino mass hierarchy and precision measurements of atmospheric neutrino mixing parameters at ICAL, and give the expected physics reach of the detector with 10 years of runtime. We also explore the potential of ICAL for probing new physics scenarios like CPT violation and the presence of magnetic monopoles.