Simulation of LHCb RICH 2025/26 Testbeam Investigating SiPM and FastRICH Upgrades

The aim of the 2025/26 RICH Testbeam is to investigate the advantages of the SiPM and the FastRICH chip, which will be implemented in future LHCb upgrades. This thesis created simulations for two of the Testbeam setups used to investigate these components. 

Initially, a simulation of the October 2025 Testbeam was created. The resulting occupancy plots of this show that SiPMs ($75\%$ occupancy) outperform the currently used MaPMTs ($50\%$ occupancy). Then a different, larger lens was simulated to compare to the current lens in the setup. The larger $200\;mm$ lens had a greater angular resolution of $4.68$ mrad, compared to $4.85$ mrad, but caused the occupancy to decrease by $14\%$ for all detectors. The differences between the lenses were insufficient to justify buying a new lens and therefore it was recommended to stick with the smaller $150\;mm$ lens. To complete the October study, timing data were simulated for the Testbeam. At thresholds of $9.8\;\mu A$ and lower, there was negligible time walk. However, at thresholds above $17.5\;\mu A$, a time walk of $350\;ps$ was observed, which increased with threshold.

Next, a design for the April 2026 Testbeam was simulated. This Testbeam will use a gas radiator instead of a lens, as this will drastically improve the Cherenkov angular resolution. Several different designs were investigated, but in the end a $1000\;mm$ gas chamber of $C_{4}F_{10}$, with the optical components aligned along the beam line, was proposed to the Testbeam team. This setup had occupancy of $35\%$ along the ring arc and Cherenkov angular resolution of $0.315$ mrad. When a beam width of $6\;mm$ was included, there was no impact on the results. Unfortunately, replacing the radiator material with $CF_{4}$, a gas with a lower refractive index, did not work in the proposed design and would require a chamber of $1700\;mm$ in length. Finally, the design was tested at low momenta in proton synchrotron conditions of $8\;GeV$. This produced an angular resolution of $0.398$ mrad and an occupancy that remained at $35\%$, which was good enough to justify using proton synchrotron conditions. The results demonstrated that the design can use non-saturated tracks and opens the possibility of particle identification in Testbeams.