The Demonstrator of the Instrumented Decay Tunnel for the ENUBET Monitored Neutrino Beam

The NP06/ENUBET project is designing a facility with unprecedented control on the neutrino flux for high precision (O(1%)) cross section measurements. An instrumented decay tunnel represents the key part of the facility, measuring large angle charged leptons from kaon decays and thus constraining the associated neutrino fluxes. It is composed by a sampling calorimeter with longitudinal, radial and azimuthal segmentation for e/μ/π separation and a rings of plastic scintillator doublets inside the calorimeter for the rejection of photons coming from π
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decays. The configuration of the calorimeter readout is the result of an intense prototyping activity. The final one is based on WLS fibers running on the frontal faces of the tiles. SiPMs collect the light from the fiber and are placed above a borated polyethylene layer, that shields against radiation damage of the sensors. To demonstrate the viability and effectiveness of the approach, a 1.65 m long section of the instrumentation with 45 deg azimuthal coverage have been built and then tested in the renovated East Area at CERN-PS. The summary of the prototyping activities, an overview of the Demonstrator design and construction and preliminary results of the test beam campaign are reported in this contribution.