The prototype phase of the ENUBET positron tagger

Understanding the interaction of neutrinos with the other particles of the Standard Model is a fundamental activity in particle physics. The uncertainties on the initial neutrino flux limit the sensitivity on the neutrino cross section measurement in the GeV range to a precision of 10-20%. The scientific goal of the ENUBET project is to improve this sensitivity up to 1% by developing an active decay tunnel, as opposed to traditional neutrino beams, which have a passive decay region. By tagging the positrons emitted in the Ke3 decay (K+ -> π0 + e+ + νe) it is possible to infer the initial neutrino flux. If the tunnel is short enough (about 50 m) the Ke3 decay is the only source of neutrinos. Shashlik calorimeters are suitable to instrument such a tunnel, because they are cost effective, have a good geometrical adaptability and their energy resolution can be tuned with the proper absorbing/scintillator tiles thickness and fiber frequency. To separate the positrons from the pion background these calorimeters are longitudinally segmented with a compact readout based on Silicon PhotoMultipliers embedded in the bulk of the calorimeter itself. This thesis describes the prototyping activity of the ENUBET Collaboration for the positron tagger and the tests performed at the CERN PS-T9 beamline from July 2016 to October 2017. The details of each prototype design and the results in terms of linearity and energy resolution are presented.