The Design of the ENUBET Beamline

The ENUBET project aims to reduce the flux-related systematics to 1% on a narrow band neutrino beam through monitoring the associated charged leptons in an instrumented decay tunnel. A key element of the project is the design of a meson transfer line with conventional magnets that maximize the yield of K+ and 𝜋+ while minimizing the total length to reduce meson decay outside the instrumented region. In order to limit particle rates in the tunnel instrumentation, a high level of beam collimation is needed, thus allowing non-decayed mesons to reach the end of the tunnel. At the same time, fine-tuning of the shielding and the collimators is required to minimize any beam-induced background in the decay region. The magnetic lattice is optimized with TRANSPORT. The focusing of mesons from the target is performed with a static (quadrupole-based) system that, coupled with a slow proton extraction scheme, allows for a significant pile-up reduction at the tunnel instrumentation while retaining a particle yield large enough for high-precision neutrino cross-section measurements on a 3 year time scale. Charge and momentum selection in an 8.5GeV ± 10% momentum bite is performed by a double dipole system. Shielding elements are optimized with full simulation of the facility in Geant4. In particular, a powerful genetic algorithm is used to scan the parameter space of the collimators automatically in order to find a configuration that minimizes the halo background in the decay tunnel while preserving a large meson yield. This contribution will report the results of the optimization studies and the final design of the ENUBET beamline, together with dose estimation through a FLUKA simulation. The design of an alternative secondary beamline with a broad momentum range (4, 6, and 8.5 GeV/c) that could enhance the physics reach of the facility is additionally discussed.