Monitored beams for high-precision neutrino flux determination: The ENUBET project

The knowledge of initial flux, energy and flavour of current neutrino beams is currently the main limitation for a precise measurement of neutrino crosssections. The ENUBET ERC project (2016-2021) is studying a facility based on a narrow-band neutrino beam capable of constraining the neutrino flux normalization through the monitoring of the associated charged leptons in an instrumented decay tunnel. In particular, the identification of large-angle positrons from K-e3 decays at single-particle level can reduce the v(e) flux uncertainty at the level of 1%. This setup would allow for an unprecedented measurement of the v(e) cross-section at the GeV scale. Such an experimental input would be highly beneficial to reduce the budget of systematic uncertainties in the next long baseline oscillation projects (i.e., HyperK-DUNE). Furthermore, in narrow-band beams, the transverse position of the neutrino interaction at the detector can be exploited to determine a priori with significant precision the neutrino energy spectrum without relying on the final-state reconstruction.