Lake- and Surface-Based Detectors for Forward Neutrino Physics

TL;DR

This work introduces SINE and UNDINE, two kiloton-scale detectors positioned at medium baselines (~18–50 km) from LHC interaction points to study forward TeV neutrinos during the HL-LHC era. Through Monte Carlo simulations with forward flux models, the authors quantify expected neutrino interactions: \\\mathcal{O}(10^7) in SINE and \\\mathcal{O}(10^5) in UNDINE, enabling measurements of TeV neutrino DIS cross sections, forward charm production, and potential strangeness enhancements; the program also opens a pathway for heavy neutral lepton searches. The study demonstrates viable background rejection strategies for a surface detector (SINE) and lake-based detector (UNDINE), and argues that these detectors offer competitive and complementary physics reach relative to the Forward Physics Facility, all at relatively modest cost. Overall, SINE and UNDINE present a practical, cost-efficient medium-baseline forward neutrino program at the HL-LHC with broad implications for hadron production, neutrino interactions, and new-physics searches.

Abstract

We propose two medium-baseline, kiloton-scale neutrino experiments to study neutrinos from LHC proton-proton collisions: SINE, a surface-based scintillator panel detector observing muon neutrinos from the CMS interaction point, and 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 $pp$ collisions, and strangeness enhancement as a solution to the cosmic-ray muon puzzle. SINE and UNDINE thus offer a cost-effective medium-baseline complement to the proposed short-baseline forward physics facility.

Figures (13)

• Figure 1: Illustration of experimental layout. Top: shows sky-view vision of the area around the LHC including potential locations for the detectors. Middle and bottom: shows a side view of the UNDINE and SINE detector setups. The shaded envelope around each beamline corresponds to the profile of the neutrino beam that passes through the FASER detector. The geometries shown in this figure are only approximate and for illustration purposes only. Illustration by Jackapan Pairin.
• Figure 1: The energy distribution (left) and radial distribution per unit area (right) of the forward neutrino flux computed in Rev. forward-nu-flux. Different distributions are shown for each of the different hadron-production models introduced in \ref{['sec:rates']}. We also show separately neutrinos from the decay of light and charm mesons.
• Figure 2: Energy distribution of events. Differential event rates as a function of neutrino energy in SINE and UNDINE. Each column corresponds to a different neutrino flavor, while each row assumes a different detector and interaction type: CC DIS in SINE (top), CC DIS in UNDINE (middle), and NC DIS in UNDINE (bottom). Each sub-figure shows the energy distribution for five different hadron-production models of the forward neutrino flux. The contribution from charm hadrons is shown separately.
• Figure 2: The distribution of neutrino-induced muon arrival times in each SINE sub-detector.
• Figure 3: Transverse displacement of signal and background in SINE. The distribution of $(\Delta x,\Delta y)$, the horizontal and vertical displacement between the front and back panels in SINE, for cosmic muon backgrounds (top) and neutrino-induced muon signals (bottom). The color axis indicates the rate during HL-LHC operation. The dotted lines and shaded regions indicate one and two-dimensional spatial cuts to separate signal from background.