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The Enhanced NeUtrino BEams from kaon Tagging or ENUBET is an ERC funded project that aims at producing an artificial neutrino beam in which the flavor, flux and energy of the produced neutrinos are known with unprecedented precision. This is accomplished by focusing mesons in a narrow band beam towards an instrumented decay tunnel, where charged leptons produced in association with neutrinos by mesons' decay can be monitored at single particle level.

Mesons (essentially pions and kaons) are produced in the interactions of accelerated protons with a Beryllium or Graphite target. The proposed facility is being studied taking into account the energies of currently available proton drivers: 400 GeV (CERN SPS), 120 GeV (FNAL Main Injector), 30 GeV (J-PARC Main Ring).

Kaons and pions are momentum and charge selected in a short transfer line by means of dipole and quadrupole magnets and are focused in a collimated beam into an instrumented decay tube. Large angle muons and positrons from kaon decays ($K^{+}\rightarrow \mu ^{+}\nu _{\mu }$, $K^{+}\rightarrow e^{+}\pi ^{0}\nu _{e}$) are measured by detectors on the tunnel walls, while muons from pion decays ($\pi ^{+}\rightarrow \mu ^{+}\nu _{\mu }$) are monitored after the hadron dump at the end of the tunnel. The decay region is kept short ($\sim$ 40 m) in order to reduce the neutrino contamination from muon decays ($\mu ^{+}\rightarrow e^{+}\nu _{e}{\bar {\nu }}_{\mu }$).

In this way the neutrino flux is assessed in a direct way with a precision of 1%, without relying on complex simulations of the transfer line and on hadro-production data extrapolation that currently limit the knowledge of the flux to 5-10%. The ENUBET facility can be used to perform precision studies of the neutrino cross section and of sterile neutrinos or Non-Standard Interaction models.

The ENUBET project started in 2016 and currently involves 12 European institutions in 5 European countries, and brings together 60 scientists.

ENUBET studies all technical and physics challenges to demonstrate the feasibility of a monitored neutrino beam: it will build a full-scale demonstrator of the instrumented decay tunnel ($\sim$ 3 m length and partial azimuthal coverage) and will assess costs and physics reach of the proposed facility.

Since March 2019, ENUBET is part of the CERN Neutrino Platform (NP06/ENUBET) for the development of a new generation of neutrino detector and facilities.