The ENUBET ERC project for an instrumented decay tunnel for future neutrino beams

The ENUBET ERC project (2016–2021) is studying a narrow band neutrino beam where lepton production can be monitored at single particle level. For this purpose, the decay tunnel is instrumented with longitudinally segmented calorimeters. Three different specialized calorimeters have been designed and tested, two of which based on the shashlik calorimetric concept with a compact readout while the third is a less compact version with a lateral readout. All of the prototypes are composed of thick steel absorbers coupled to plastic scintillators. Regarding the shashlik modules, a matrix of 3 × 3 fibers runs transversely with a density of one fiber/cm$^2$ . The fibers are coupled individually to silicon photomultipliers mounted on a custom PCB allowing to reduce the dead zones between adjacent modules to an extremely small level compared to the “fiber bundling” configurations. This setup allows a very effective longitudinal segmentation and hence $e / \pi$ separation. The second shashlik module is based on polysiloxane scintillators which come in liquid form, are poured around the fiber arrays and finally made solid with a thermal treatment. Finally, the lateral readout module, light is collected from both sides of each scintillator tile and the 10 fibers from the same UCM are bundled to a single SiPM. Here are discussed the results of test beams performed in 2016–2018 at the CERN-PS East Area and the characterization of SiPMs of different cell size ( 12 μm and 15 μm ) before and after being exposed to neutron fluxes up to 10$^{12}$ /cm$^2$ at the INFN-LNL CN accelerator facility.