Beam Test Performance of AstroPix sensor with 120 GeV protons

TL;DR

This study evaluates AstroPix_v3, a high-voltage CMOS MAPS sensor, in a 120 GeV proton beam at FTBF to quantify its MIP response and extract an effective silicon depletion depth. Using pixel-level calibrations and beam-profile analyses, the authors determine a mean MIP energy of 35.4 keV and a depletion depth of 133 μm, with thorough systematic checks and cross-validation via Geant4 simulations. The results validate the sensor’s dynamic range for MIP measurements and provide a robust input for detector simulations in the BIC of the ePIC detector, while outlining a roadmap for multi-chip modules and further AstroPix iterations toward large-area imaging layers. Overall, the work demonstrates precise energy deposition measurements in AstroPix_v3 and establishes groundwork for scalable, fully-depleted HV-CMOS MAPS in future collider and space applications.

Abstract

AstroPix is a high-voltage CMOS (HV-CMOS) monolithic active pixel sensor (MAPS) developed for precision gamma-ray imaging and spectroscopy in the medium energy regime, as well as for precise shower imaging and tracking in the Barrel Imaging Calorimeter (BIC) of the Electron Proton/Ion Collider (ePIC) detector at the future Electron-Ion Collider (EIC). We present beam test results of the AstroPix v3 sensor using a 120 GeV proton beam at the Fermilab Test Beam Facility (FTBF), performed as part of the broader experimental campaign for the BIC prototype calorimeter. The sensor's 500 um pixel pitch enabled precise measurement of the beam profile, providing important information for calorimeter performance studies. Using the measured 120 GeV proton data, we measure the energy deposit of minimum ionizing particles and use them to extract the corresponding effective depletion depth.

Figures (11)

• Figure 1: Bench test setup with AstroPix_v3 single chip.
• Figure 2: Noise map obtained at a 200 mV threshold, presenting the dark count rate across the pixel array.
• Figure 3: One example of the single-pixel ToT spectra from the $^{241}$Am and $^{133}$Ba measurements is shown. The photopeaks are identified and fitted with Gaussian functions. The green and blue lines correspond to the $^{241}$Am and $^{133}$Ba spectra, respectively, and the dotted lines indicate the fitted Gaussian functions.
• Figure 4: Calibration curves for all selected pixels of a single AstroPix_v3 chip. Blue lines show fits with the second-degree polynomial function to the mean ToT values extracted from Gaussian fits to the ToT distributions at three gamma energies (31, 59.5, and 81 keV). The upper panels display the distributions of the mean ToT values across pixels for each energy, illustrating pixel-to-pixel variations. The green and yellow bands indicate the 68% and 95% central intervals around the median, respectively.
• Figure 5: (Top) Example ToT spectra for injection voltages from 100 mV to 300 mV. All ToT distributions are fitted with a Gaussian function. (Bottom) Example fitting results for ToT value as a function of injection voltages using two fit functions: an empirical function (red line) and a second-degree polynomial function (blue dotted line).