The ENUBET narrow band neutrino beam

ENUBET has been conceived to monitor positrons from $K_{e3}$ decays in conventional neutrino beam decay tunnels in order to provide a direct determination of the $\nu_e$ flux at the source, paving the way to a measurement of electron neutrino cross section with 1% precision. Since 2016 remarkable results on the prototyping and testing of the tunnel instrumentation for positron tagging have been achieved, as well as on the design and simulation of the proton extraction scheme, the focusing system and the meson transfer line. In particular the demonstration of the viability of a static focusing extend the potential of monitored neutrino beams beyond the original aim of ENUBET: the flux measurement at the 1% level also for $\nu_{\mu}$ produced in the beam. Particular emphasys will be given on this topic and on the possibility to determine the neutrino energy without relying on final state particle reconstruction, thanks to the narrow momentum width of the selected mesons.