Lake- and surface-based detectors for forward neutrino physics

We propose two medium-baseline, kiloton-scale neutrino experiments to study neutrinos from LHC proton-proton collisions: the Surface-based Integrated Neutrino Experiment (SINE), a surface-based scintillator panel detector observing muon neutrinos from the compact muon solenoid interaction point, and the UNDerwater Integrated Neutrino Experiment (UNDINE), a water Cherenkov detector submerged in lake Geneva observing all-flavor neutrinos from LHCb. Using a Monte Carlo simulation, we estimate millions of neutrino interactions during the high-luminosity LHC era. We show that these datasets can constrain neutrino cross sections, charm production in p p collisions, strangeness enhancement as a solution to the cosmic-ray muon puzzle, and heavy neutral leptons. SINE and UNDINE thus offer a cost-effective medium-baseline complement to the proposed short-baseline forward physics facility.