Experimental layout for the direct measurement of electromagnetic shower acceleration in an oriented crystal scintillator

Progress in experimental high-energy physics has been closely tied to developments of high-performance calorimeters. Since their invention, crystal calorimeters have consistently achieved the best resolution for measurements of the energies of electromagnetic (e.m.) particles (electrons and photons). Recently, we experimentally demonstrated the possibility of significantly accelerating the e.m. shower development inside lead tungstate (PWO) crystal when the incident beam is aligned with the crystal axes within some tenths of a degree. Here, we present the innovative photodetection system, based on Silicon PhotoMultipliers, implemented for the direct measurement of the scintillation light enhancement in case of beam aligned to the main crystal axes, along with its characterization performed with cosmic rays at the Insulab laboratory (Insubria University, Como). In 2021 we performed a test at H2 beam line of CERN SPS with a hundred-GeV electron beam with two PWO samples (1 and 2 X0 thick) directly coupled with SiPMs. Since the angular acceptance of the crystal strong field depends weakly on particle energy, while instead the decreasing of the shower length remains pronounced at very high-energy, a crystal calorimeter based on oriented crystals would feature a consistent compactness enhancement while rivaling the current state of the art in terms of resolution in the range of interest of present and future forward detectors, beam dumps for light dark matter search and source-pointing space-borne γ-ray telescopes.