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 <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>p</a:mi> <a:mi>p</a:mi> </a:math> 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.