First Measurement of the Muon Neutrino Interaction Cross Section and Flux as a Function of Energy at the LHC with FASER

TL;DR

This paper reports the first differential measurement of muon neutrino interaction cross section and flux as a function of energy at the LHC, using FASER detector data at 13.6 TeV.

Contribution

It provides the first energy-dependent neutrino cross section and flux measurements in the TeV range at the LHC, validating Standard Model predictions.

Findings

Measured 338.1 ± 21.0 charged current muon neutrino interactions.

Achieved the first differential measurement in the TeV energy range.

Aligned observed distributions with Standard Model predictions.

Abstract

This letter presents the measurement of the energy-dependent neutrino-nucleon cross section in tungsten and the differential flux of muon neutrinos and anti-neutrinos. The analysis is performed using proton-proton collision data at a center-of-mass energy of $13.6 \, {\rm TeV}$ and corresponding to an integrated luminosity of $(65.6 \pm 1.4) \, \mathrm{fb^{-1}}$. Using the active electronic components of the FASER detector, $338.1 \pm 21.0$ charged current muon neutrino interaction events are identified, with backgrounds from other processes subtracted. We unfold the neutrino events into a fiducial volume corresponding to the sensitive regions of the FASER detector and interpret the results in two ways: We use the expected neutrino flux to measure the cross section, and we use the predicted cross section to measure the neutrino flux. Both results are presented in six bins of neutrino energy, achieving the first differential measurement in the TeV range. The observed distributions align with Standard Model predictions. Using this differential data, we extract the contributions of neutrinos from pion and kaon decays.