The LHC as a Neutrino-Ion Collider

TL;DR

This paper explores how neutrino interactions produced at the LHC can be used as a new tool for probing proton and nuclear structure, significantly reducing uncertainties in parton distribution functions and improving predictions for key collider processes.

Contribution

It demonstrates that LHC neutrino data can serve as a novel neutrino-ion collider, enhancing global PDF analyses without requiring new infrastructure modifications.

Findings

Up to one million neutrino DIS interactions expected at HL-LHC.

Significant reduction in PDF uncertainties, especially for strangeness and valence quarks.

Improved predictions for Higgs and gauge boson production at the LHC.

Abstract

Proton-proton collisions at the LHC generate a high-intensity collimated beam of neutrinos in the forward (beam) direction, characterised by energies of up to several TeV. The recent observation of LHC neutrinos by FASER$\nu$ and SND@LHC signals that this hitherto ignored particle beam is now available for scientific inquiry. Here we quantify the impact that neutrino deep-inelastic scattering (DIS) measurements at the LHC would have on the parton distributions (PDFs) of protons and heavy nuclei. We generate projections for DIS structure functions for FASER$\nu$ and SND@LHC at Run III, as well as for the FASER$\nu$2, AdvSND, and FLArE experiments to be hosted at the proposed Forward Physics Facility (FPF) operating concurrently with the High-Luminosity LHC (HL-LHC). We determine that up to one million electron- and muon-neutrino DIS interactions within detector acceptance can be expected by the end of the HL-LHC, covering a kinematic region in $x$ and $Q^2$ overlapping with that of the Electron-Ion Collider. Including these DIS projections into global (n)PDF analyses, specifically PDF4LHC21, NNPDF4.0, and EPPS21, reveals a significant reduction of PDF uncertainties, in particular for strangeness and the up and down valence PDFs. We show that LHC neutrino data enables improved theoretical predictions for core processes at the HL-LHC, such as Higgs and weak gauge boson production. Our analysis demonstrates that exploiting the LHC neutrino beam effectively provides CERN with a "Neutrino-Ion Collider" without requiring modifications in its accelerator infrastructure.