SiPM non-linearity studies in beam tests with scintillating crystals

TL;DR

This study investigates the non-linear response of high-pixel-density SiPMs coupled with scintillating crystals in beam tests, providing calibration methods and quantifying deviations at high photoelectron counts for future calorimeter applications.

Contribution

It presents a detailed experimental analysis of SiPM non-linearity in realistic beam conditions, introducing a dual-end readout calibration scheme for high dynamic range measurements.

Findings

SiPM non-linearity reaches about 20% at 500,000 photoelectrons for BGO.

Larger non-linearity deviations observed in NDL devices and faster BSO scintillators.

Beam tests at CERN SPS validated the calibration method and quantified SiPM response.

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~$\mu$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.