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Description
Accurate luminosity measurements are essential for stable machine operation and precision physics at the High-Luminosity LHC (HL-LHC), where pileup levels exceeding 140 interactions per bunch crossing impose stringent requirements on fast and radiation-tolerant instrumentation. The Beam Monitoring detector for ATLAS (BMA) is a newly developed luminosity system designed to deliver robust, bunch-by-bunch measurements throughout HL-LHC operations. Its design is based on Low-Gain Avalanche Diodes (LGADs), which provide intrinsically fast signal rise times, high signal-to-noise ratio (SNR), and strong radiation tolerance - key features for resolving individual 25 ns bunch crossings in the HL-LHC environment.
This contribution presents the BMA detector architecture, including the LGAD sensor layout and the readout chain, all designed to operate under the high particle fluences expected at the installation position. The amplification of the detectors signal occurs far from the detector, allowing to reduce the radiation damage to the electronics, but still maintaining a high SNR. We report results from laboratory characterisation as well as the performance of prototype BMA detectors installed in ATLAS during the 2022–2025 data-taking periods. The LGADs performance - such as efficiency, gain stability, and gain degradation after irradiation - are analysed.
The results provide an assessment of the LGAD technology as a beam-monitor and luminosity detector in the LHC environment, indicating that the gain and the particle detection efficiency, relevant for bunch-by-bunch luminosity measurements, can be retained under HL-LHC conditions.