Low Gain Avalanche Diodes for Beam Monitoring and Reaction Time Determination at High Rates in HADES

The Low Gain Avalanche Diode (LGAD) technology enables high precision timing in the order of σₜ ≈ 30 ps for Minimum Ionizing Particles (MIPs), while simultaneously featuring high spatial resolution and excellent radiation hardness (operational up to fluences of Φₙₑ > 10¹⁵ nₑ/cm²). This technology sparked interest in the High Energy Physics (HEP) community for example for 4D-trackers (i.e. track reconstruction in coordinate space and time), beam monitoring and even medical applications. Due to those excellent properties of LGADs, the High Acceptance Di-Electron Spectrometer (HADES) collaboration employed LGADs as sensors for its in-beam Start detector, responsible for reaction time (T0) determination as well as beam spatial and time structure monitoring for the high rate p+p production beam time with a beam kinetic energy of 4.5 GeV in February 2022. Therefore, a dedicated HADES LGAD production was launched at Fondazione Bruno Kessler. This work will focus on the application of LGADs for the HADES Start detector and the fulfillment of the above mentioned tasks. After a presentation of the HADES LGAD production, the results of the full system test for the LGAD-based Start detector will be presented, indicating the viability of using LGADs for the purposes of the HADES Start detector. The performance as a beam time-structure monitoring tool at the p+p experiment will be shown, followed by a detailed discussion on the applied calibration and T0 reconstruction algorithms. The performance of the LGAD-based Start detector will be presented w.r.t. the reached T0 reconstruction efficiency and its precision as well as the sensor efficiency and radiation hardness over the entire p+p production beam time. After a full calibration of the sensor, T0s could be reconstructed with precisions of σ(T0) < 90 ps, when both sensors were used for the reconstruction, while single sensor T0 precisions up to σ(T0) ≈ 120 ps were achieved. The performance of the LGAD sensors deteriorated after the accumulation of radiation damage. Its effect will be presented for a selected single sensor. In order to demonstrate the excellent T0 reconstruction precision and accuracy, an analysis of the inclusive charged pion production was conducted employing only a particle identification via time of flight and momentum measurements. The resulting inclusive production cross section of σ(π⁺) ≈ (35.3 ± 4.6) mb and σ(π⁻) ≈ (9.7 ± 1.5) mb will be put into context with measurements of other experiments using p+p collisions.