A SHIFT of Perspective: Observing Neutrinos at CMS and ATLAS

TL;DR

SHIFT@LHC proposes a gaseous fixed target near the LHC interaction points to produce forward neutrinos from proton–gas collisions that can be detected in CMS and ATLAS. Using PYTHIA8 to simulate proton–gas collisions, rock propagation with GEANT4, and GENIE for neutrino interactions, the study estimates event yields for $1\%$ of Run-4 luminosity. The results indicate about $O(10^4)$ $\nu_\mu$ CC and $O(10^3)$ $\nu_e$ CC interactions across a neutrino energy range of $20$ GeV to $1$ TeV. The work highlights forward-physics access and potential impact on atmospheric-neutrino experiments, while noting challenges such as muon-background separation and pileup, motivating further detailed simulations and target-geometry optimization.

Abstract

We investigate the physics potential of SHIFT@LHC, a proposed gaseous fixed target installed in the LHC tunnel, as a novel source of detectable neutrinos. Using simulations of proton-gas collisions, hadron propagation, and neutrino interactions, we estimate that $O(10^4)$ muon-neutrino and $O(10^3)$ electron-neutrino interactions, spanning energies from 20 GeV to 1 TeV, would occur in the CMS and ATLAS detectors with 1% of the LHC Run-4 integrated luminosity. This unique configuration provides access to hadron production in the pseudorapidity range 5<$η$<8, complementary to existing LHC detectors. If realized, this would mark the first detection of neutrinos in a general-purpose LHC detector, opening a new avenue to study neutrino production and interactions in a regime directly relevant to atmospheric neutrino experiments.

Figures (5)

• Figure 1: Distribution of the production and interaction vertices of neutrinos with the gaseous target placed 160 meters away from IP5 (top) and IP1 (bottom). The production points are shown for neutrinos interacting in the CMS and ATLAS calorimeters, in which darker (lighter) red indicate the regions where there are more (less) decay vertices. The interaction vertices are shown for all subdetectors, in which yellow (blue) colors indicate the regions where there are more (less) interactions. The fiducial volumes of the calorimeters used in this analysis are marked with red lines.
• Figure 2: Energy distribution of neutrino and antineutrino CC interactions in the tracker and calorimeters of CMS (top) and ATLAS (bottom). Colors represent different neutrino flavors. Dashed, and dotted lines indicate neutrinos produces in pion and kaon decay respectively.
• Figure 3: Relative change in the electron- and muon-neutrino interaction rate as a function of the target location with respect to IP5.
• Figure 4: Parent pseudorapidity and radial distributions of $\nu_\mu+\bar{\nu}_\mu$ CC interactions in CMS and ATLAS. The center panel shows the average pseudorapidity as function of the radial distribution.
• Figure 5: Expected energy distribution of muon neutrinos measurable in CMS and ATLAS with SHIFT, compared to FASER and SND@LHC projections Kling:2021gos. FASER and SND@LHC results are scaled to 715 fb$^{-1}$, corresponding to the LHC Run-4 integrated luminosity. For SHIFT, 1% of the Run-4 integrated luminosity is assumed, following Niedziela:2024khw.