Commissioning of proANUBIS: A proof-of-concept detector for the ANUBIS experiment

Abstract: Long-lived particles (LLPs), predicted by various extensions of the Standard Model (SM), have become a key focus of the contemporary search programme for physics beyond the SM. To enhance LLP discovery potential at the LHC, the ANUBIS experiment has been proposed to instrument the ceiling of the ATLAS experiment's underground cavern with dedicated tracking detectors. This report summarises recent progress towards realising ANUBIS. Specifically, a key milestone has been achieved with the installation and commissioning of proANUBIS, a prototype that serves as a proof-of-concept for ANUBIS. We describe the proANUBIS setup, including its remotely-operated data acquisition system and automatic signal processing chain. The proANUBIS demonstrator is used to evaluate the detector performance under realistic conditions in the UX1 ATLAS experimental cavern, including readout synchronisation with the ATLAS experiment. Furthermore, proANUBIS allows for the direct measurement of relevant background processes in a representative location within the ATLAS cavern, providing input for the simulation of such processes for the future ANUBIS detector. The paper concludes with an update on the current status of the ANUBIS project and its roadmap toward a full-scale implementation in the ATLAS cavern.