The ENUBET project: a monitored neutrino beam

The ENUBET project intends to reduce the flux related systematics in an accelerator neutrino beam to the 1% level by monitoring associated charged leptons produced in a narrow band meson beam. Large angle leptons from kaon decays are measured in an instrumented decay tunnel, while low angle muons from pions can be monitored after the hadron dump. A key element of the project is the design of a meson transfer line with conventional magnets that maximizes the yield of K+ and π+, while minimizing the total length to reduce meson decays in the not instrumented region. The transfer line is optimized for 8.5 GeV/c mesons with a momentum bite of 5-10%, considering various proton drivers and target designs and it is based on conventional quadrupoles and dipoles and provides a large bending angle that can ensure a reduced background from the untagged neutrino component at the neutrino detector. The ENUBET Collaboration presented at NuFact2021 the latest design of the hadron beam line, the performance of the positron tagger prototypes tested at CERN beamlines, a full simulation of the positron reconstruction chain and the expected physics reach.