SiPM non-linearity studies in beam tests with scintillating crystals

Abstract

High-granularity homogeneous electromagnetic calorimeters based on scintillating crystals and silicon photomultipliers (SiPMs) are a promising option for future $e^{+}e^{-}$ Higgs factories, where both excellent energy resolution and a very large dynamic range are required. In this work, the non-linear response of high-pixel-density SiPMs with pixel pitches of 6--10~$μ$m coupled to BGO and BSO crystals is studied under realistic beam conditions. A dual-end readout scheme with an attenuated reference SiPM was employed to precisely calibrate the deposited energy and the corresponding number of photoelectrons over a wide dynamic range. Beam tests were carried out at the CERN SPS H2 beamline using high-energy electrons, with a tungsten pre-shower and variable incident angles to enhance energy deposition. The measurements directly quantify the non-linear response of SiPMs to scintillation light over an extended dynamic range. For BGO-coupled Hamamatsu SiPMs, deviations from linearity of about 20\% are observed at $5\times10^{5}$ photoelectrons, while larger deviations are measured for the tested NDL devices and for configurations with faster BSO scintillation.

Figures (15)

• Figure 1: Schematic view of the experimental concept based on dual-end SiPM readout of a crystal bar.
• Figure 2: Geant4 simulation setup used for the pre-shower optimization studies.
• Figure 3: Energy absorbed in the crystal as a function of pre-shower thickness for different incident angles: (a) $90^\circ$, (b) $60^\circ$, and (c) $30^\circ$ with respect to the crystal longitudinal axis.
• Figure 4: Photograph and schematic view of the experimental setup.
• Figure 5: Photographs of the SiPM board and the pre-amplifier board.