The ENUBET monitored neutrino beam.

The main source of systematic uncertainty on neutrino cross- section measurements at the GeV scale is represented by the poor knowledge of the initial flux. The ENUBET project has been funded by the ERC in 2016 with the goal of cutting down this uncertainty to 1% through the monitoring of charged leptons produced in association with neutrinos, by properly instrumenting the meson decay region of a conventional narrow-band neutrino beam. Large angle muons and positrons from kaons are measured by a sampling calorimeter on the decay tunnel walls (tagger), while muon stations after the hadron dump can be used to monitor the neutrino component from pion decays, thus providing a full control on both the muon and electron neutrino fluxes. Furthermore, the narrow momentum width ($< 10$%) of the beam provides a precise measurement ($O(10%)$) of the neutrino energy on an event-by-event basis, thanks to its correlation with the radial position of the interaction at the neutrino detector. This contribution will report the final design of the horn-less beamline together with the assessment of the systematic budget on the neutrino flux. The construction of the tagger demonstrator will be also discussed.