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Main Authors: Mondal, D., Baker, W., Chaudhuri, M., Dent, J. B., Dutta, B., Iyer, V., Jastram, A., Kashyap, V. K. S., Kubik, A., Lang, K., Mahapatra, R., Maludze, S., Mirabolfathi, N., Mirzakhani, M., Mohanty, B., Neog, H., Newstead, J. L., Platt, M., Sahoo, S., Sander, J., Strigari, L. E., Walker, J.
Format: Preprint
Published: 2026
Subjects:
Instrumentation and Detectors
High Energy Physics - Experiment
Online Access:https://arxiv.org/abs/2605.31190
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Table of Contents:
  • As cryogenic detectors push toward ever-lower energy thresholds, their sensitivity is increasingly constrained by a persistent low-energy background known as the low-energy excess (LEE). We report observation of LEE in the MINER experiment using a sapphire ($\mathrm{Al_2O_3}$) detector at energies around 200 eV, with the excess reproducibly reappearing after each non-operational warm-up period. To address this limiting background, we implement an unsupervised convolutional variational autoencoder (CVAE) framework that identifies anomalous events through a reconstruction-based anomaly score. For the first time in a pulse-shape driven analysis, we uncover a significant deviation in the rise-time of LEE events relative to Monte Carlo simulated ideal signals. Using this feature, we develop a discrimination pipeline based on rise-time selection. This method achieves up to 53\% rejection of LEE events, corresponding to an expected sensitivity improvement of nearly 10\% for MINER at HFIR. These findings are consistent with a scenario in which a substantial fraction of the LEE originates from bulk-related defects or microfractures within the detector crystal, while leaving room for additional detector-related contributions. Our result provides a powerful, data-driven pathway for mitigating LEE and enhancing the discovery potential of next-generation cryogenic experiments.

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