Predictions for neutrinos and new physics from forward heavy hadron production at the LHC

Scenarios with new physics particles feebly interacting with the Standard Model sector provide compelling candidates for dark matter searches. Geared with a set of new experiments for the detection of neutrinos and long-lived particles, such as the FASER detector, the Large Hadron Collider (LHC) has joined the hunt for these elusive states. On the theoretical side, this emerging physics program requires reliable estimates of the associated particle fluxes, in particular those arising from heavy hadron decays. In this work, we provide state-of-the-art QCD predictions for heavy hadron production including radiative corrections at next-to-leading order and small-$x$ resummation at next-to-leading logarithmic accuracy. We match our predictions to parton showers to provide a realistic description of hadronisation effects. We demonstrate the utility of our predictions by presenting the energy spectrum of neutrinos from charm hadron decays. Furthermore, we employ our predictions to estimate, for the first time, FASER's sensitivity to electrophilic ALPs, which are predominantly generated in beauty hadron decays.