Theory overview on neutrino studies and outlook

Abstract

The forward neutrino program at the Large Hadron Collider has entered the era of providing the first measurements and observations. As it has notable connections to astrophysics and will complement the results and projections of key measurements at the LHC and other measurements, it is becoming increasingly important for collider physicists to recognize and utilize the unique potential of this novel research direction. The present work reviews a selection of questions related to the nature, masses and interactions of neutrinos, and highlights some of the recent projections for the LHC Run 3 as well as the high-luminosity run.

Figures (2)

• Figure 1: The composition of CC interaction spectra for incoming $\nu_\mu+\overline{\nu}_\mu$ (left) and $\nu_e+\overline{\nu}_e$ (middle) for a hypothetical detector assuming perfect lepton identification. This constrains forward hadron production, as pions do not contribute to the $\nu_e$ spectrum consisting mainly of kaons and charmed hadrons. Further constraining power can be obtained with reliable final state lepton charge identification, as hyperons decay only to $\overline{\nu}_e$Kling:2025lnt. Additionally, the characteristic changes induced on the spectra by enhanced strangeness production and proton intrinsic charm models are illustrated qualitatively. The consequences of poor lepton identification are depicted for a case where low-energy $\nu_e$CC events are indistinguishable from neutral current (NC) interactions, and $\pi$ contributions leak into observed $\nu_e$ spectra via $\nu_\mu$NC (right). Image after Ref. Ariga:2025jgv.
• Figure 2: Left:$2\sigma$ constraints (gray) for $f_s$ at FASER$\nu$ and FPF, and the FASER$\nu$ discovery potential (turquoise), with and without $\nu_\tau$ and high-$E$$\nu_e$ contributions. All bounds cover the region favored by the enhanced strangeness solution to the muon puzzle (dark green), though the effect may be more subtle at the LHC (light green) Kling:2023tgr. Middle: Projected FASER$\nu$(2) sensitivities to NSI operators violating lepton flavor universality Kling:2023tgrAdhikary:2024nlv. Right: 95% confidence level sensitivities to axial and vector coupling modifications due to NSI affecting trident measurements. The DUNE bounds (dashed brown) assume a 25% uncertainty cross section measurement. The FASER$\nu$2 bounds (teal) are based on 100% and 25% of expected data. The NuTeV bound is found assuming a BSM/SM cross section ratio equal to CCFR due to similar energy Altmannshofer:2024hqd.