Measurement of Muon Neutrinos as a Function of Energy and Rapidity with FASER

We present a double-differential measurement of the muon neutrino flux and neutrino--nucleon cross section as functions of neutrino energy $E$ and rapidity $y$, using proton--proton collision data at $\sqrt{s} = 13.6$~TeV recorded during LHC Run~3, corresponding to an integrated luminosity of $(186 \pm 4) ~\text{fb}^{−1}$. Charged-current muon neutrino interactions are identified using the active electronic components of the FASER detector, enabling the measurement of the neutrino flux as a function of rapidity in the far-forward region of the LHC. After subtracting the expected backgrounds, $766.8 \pm 29.6$ interaction events are observed. We unfold the neutrino events into a fiducial volume corresponding to the sensitive regions of the FASER detector. These results provide the first double-differential characterization of TeV-scale collider neutrinos in energy and rapidity and contribute to a detailed experimental mapping of the forward neutrino flux at the LHC.