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

TL;DR

The paper documents the design, construction, and commissioning of proANUBIS, a BIS7 RPC-based prototype aimed at validating the ANUBIS detector concept for long-lived particle searches at the LHC. It covers three-layer tracking geometry (bottom triplet, middle singlet, top doublet), QA/QC across gas gaps and front-end electronics, and a hybrid DAQ system with trigger logic aligned to LHC timing. Performance studies with cosmic-ray muons establish high efficiency (>95%), low noise, and stable operation, culminating in successful on-surface commissioning and underground deployment. The work provides essential empirical input for refining MC simulations, detector layout, and background rejection for the full-scale ANUBIS project, and reports notable data-taking milestones (104 fb$^{-1}$ in 2024 and 73 fb$^{-1}$ in 2025) that guide future upgrades and integration strategies.

Abstract

The ANUBIS experiment aims to search for long-lived particles at the Large Hadron Collider (LHC) at CERN. To assess the feasibility of the project, a prototype detector, proANUBIS, was designed, constructed, and prepared for installation in the UX1 ATLAS experimental cavern at the LHC. The primary physics goals of proANUBIS are to determine the technical limitations of the detector technology and to explore the ANUBIS detector concept through in-situ measurements of muon and hadron fluxes inside the ATLAS cavern, which can be used to refine Monte Carlo simulations of such fluxes further. This report describes the design and construction of the proANUBIS experimental setup using Resistive Plate Chambers (RPCs), highlighting the possible future use case of the technology for ANUBIS. Details on the RPC technology, construction processes, quality control measures, and performance studies are discussed. Furthermore, the RPC front-end on-detector electronics and data acquisition components of proANUBIS are presented.

Figures (16)

• Figure 1: The layout of the underground cavern at Point 1 of the LHC, featuring the ATLAS experiment represented in black. Additionally, the PX14 and PX16 access shafts are shown. The red-coloured area illustrates the current configuration of the ANUBIS experiment, to be positioned on the ceiling of the ATLAS UX1 underground cavern.
• Figure 2: (a) The design of the proANUBIS detector, showcasing the positioning of the three integrated tracking layers. (b) The arrangement of the tracker components within the proANUBIS setup. At the bottom, three RPCs (a triplet) are shown, followed by a singlet in the middle, and a doublet on top.
• Figure 3: A 6U VME crate with proANUBIS DAQ components from left to right: the CAEN V4718 Ethernet controller card, six CAEN V767 TDCs, a signal translator board, the trigger logic board, and eleven trigger boards that are referred to as "OR boards".
• Figure 4: The data flow diagram of the proANUBIS DAQ system up to the data recording stage.
• Figure 5: One of the gas gaps upon reception at CERN. The white patches on the gas gap mark the positions of the spacers.