We propose to build and operate a detector that will, for the first time, measure the process pp → νX at the LHC and search for feebly interacting particles (FIPs) in an unexplored domain. The TI18 tunnel has been identified as a suitable site to perform these measurements due to very low machine-induced background. The detector will be off-axis with respect to the ATLAS interaction point (IP1) and, given the pseudo-rapidity range accessible, the corresponding neutrinos will mostly come from charm decays: the proposed experiment will thus make the first test of the heavy flavour production in a pseudo-rapidity range that is not accessible to the current LHC detectors. In order to efficiently reconstruct neutrino interactions and identify their flavour, the detector will combine in the target region nuclear emulsion technology with scintillating fibre tracking layers and it will adopt a muon identification system based on scintillating bars that will also play the role of a hadronic calorimeter. A time of flight measurement will also be achieved thanks to a dedicated timing detector. The operation of this detector will provide an important test of neutrino reconstruction in a high occupancy environment in view of a possible experiment at HL-LHC or at the SPS Beam Dump Facility.
