ANUBIS: AN Underground Belayed In-Shaft experiment to search for long-lived particles using LHC service shafts at CERN
Lead Research Organisation:
UNIVERSITY OF CAMBRIDGE
Abstract
The Standard Model (SM) of Elementary Particle Physics is the most fundamental and predictive theory to date. Yet, it fails to answer several fundamental questions about:
The particulate nature of Dark Matter (DM), which comprises 4/5 of the mass in the Universe;
The mechanism of baryogenesis, i.e., the origin of the matter-antimatter asymmetry in the Universe;
The origin of neutrino masses that cannot be explained by the Higgs mechanism;
etc.
Many Beyond the SM (BSM) theories addressing the above questions predict long-lived particles (LLPs) with macroscopic lifetimes of >10 ns. Typically, the LLP lifetime is a free parameter in these BSM theories, and can range from 10 ns to 0.1 s, the Big Bang Nucleosynthesis limit.
Even though LLPs may be copiously produced at the LHC, detecting them poses significant experimental challenges:
The main LHC detectors are limited by their finite detector volumes, intricate backgrounds, and trigger requirements. As a result, LLPs can escape detection, especially if they are electrically neutral and tend to decay outside the active detector volume due to long lifetimes;
Dedicated forward detectors like FASER and fixed-target experiments like SHiP can probe long lifetimes in some scenarios. However, due to kinematic restrictions, these experiments cannot probe for LLPs produced via massive mediators at the electroweak scale and above;
This sensitivity gap can be addressed by ANUBIS, a transverse detector, at the High-Luminosity LHC.
The ANUBIS detector foresees instrumenting the ceiling of the ATLAS UX1 experimental cavern and the bottoms of the PX14 and PX16 service shafts with tracking stations, thereby creating a large, air-filled decay volume of 15,000 m3. This setup provides an up to 100x better sensitivity compared to existing and approved future experiments at a very moderate cost by leveraging the existing ATLAS detector and cavern infrastructure.
Together with my FLF team and international ANUBIS collaborators, we have been working hard towards realising ANUBIS in the first FLF part. We have provided extensive sensitivity studies of ANUBIS' sensitivity to potential LLP scenarios endorsed by the Physics Beyond Colliders group of CERN, working out a rigorous background estimate and focusing on Higgs portal, baryogenesis, heavy neutral leptons, and axion-like particle scenarios. On the experimental side, we have finalised the ANUBIS detector geometry, and currently focus on the detector layout optimisation. Moreover, we constructed, deployed, commissioned and are now taking data with proANUBIS, a demonstrator of the ANUBIS detector. Furthermore, we have an active R&D programme towards validating eco-friendly gas mixtures for use in ANUBIS. In parallel, we have maximised the sensitivity of ATLAS to LLPs with lifetimes of around 10 ns, and provided world-leading limits on photophobic ALP limits. Beyond this, we have brought the muon tomography project ScanMu to TRL2, and instigated a new collaboration with a commercial partner GScan and DESY.
In the second FLF part, my primary goal is LHCC approval of ANUBIS, finalising the Letter of Intent, finishing the Detector R&D work, developing a Technical Design, maturing the ANUBIS Collaboration, and securing funding for its realisation, both nationally and internationally. In parallel, my goal is harvesting the physics results after optimising the sensitivity of ATLAS to LLP decaying in the muon spectrometer in the first FLF part. Beyond this, I aim to extend my academic profile and continuing my work on ScanMu with international partners, exploring a new muon imaging concept.
The particulate nature of Dark Matter (DM), which comprises 4/5 of the mass in the Universe;
The mechanism of baryogenesis, i.e., the origin of the matter-antimatter asymmetry in the Universe;
The origin of neutrino masses that cannot be explained by the Higgs mechanism;
etc.
Many Beyond the SM (BSM) theories addressing the above questions predict long-lived particles (LLPs) with macroscopic lifetimes of >10 ns. Typically, the LLP lifetime is a free parameter in these BSM theories, and can range from 10 ns to 0.1 s, the Big Bang Nucleosynthesis limit.
Even though LLPs may be copiously produced at the LHC, detecting them poses significant experimental challenges:
The main LHC detectors are limited by their finite detector volumes, intricate backgrounds, and trigger requirements. As a result, LLPs can escape detection, especially if they are electrically neutral and tend to decay outside the active detector volume due to long lifetimes;
Dedicated forward detectors like FASER and fixed-target experiments like SHiP can probe long lifetimes in some scenarios. However, due to kinematic restrictions, these experiments cannot probe for LLPs produced via massive mediators at the electroweak scale and above;
This sensitivity gap can be addressed by ANUBIS, a transverse detector, at the High-Luminosity LHC.
The ANUBIS detector foresees instrumenting the ceiling of the ATLAS UX1 experimental cavern and the bottoms of the PX14 and PX16 service shafts with tracking stations, thereby creating a large, air-filled decay volume of 15,000 m3. This setup provides an up to 100x better sensitivity compared to existing and approved future experiments at a very moderate cost by leveraging the existing ATLAS detector and cavern infrastructure.
Together with my FLF team and international ANUBIS collaborators, we have been working hard towards realising ANUBIS in the first FLF part. We have provided extensive sensitivity studies of ANUBIS' sensitivity to potential LLP scenarios endorsed by the Physics Beyond Colliders group of CERN, working out a rigorous background estimate and focusing on Higgs portal, baryogenesis, heavy neutral leptons, and axion-like particle scenarios. On the experimental side, we have finalised the ANUBIS detector geometry, and currently focus on the detector layout optimisation. Moreover, we constructed, deployed, commissioned and are now taking data with proANUBIS, a demonstrator of the ANUBIS detector. Furthermore, we have an active R&D programme towards validating eco-friendly gas mixtures for use in ANUBIS. In parallel, we have maximised the sensitivity of ATLAS to LLPs with lifetimes of around 10 ns, and provided world-leading limits on photophobic ALP limits. Beyond this, we have brought the muon tomography project ScanMu to TRL2, and instigated a new collaboration with a commercial partner GScan and DESY.
In the second FLF part, my primary goal is LHCC approval of ANUBIS, finalising the Letter of Intent, finishing the Detector R&D work, developing a Technical Design, maturing the ANUBIS Collaboration, and securing funding for its realisation, both nationally and internationally. In parallel, my goal is harvesting the physics results after optimising the sensitivity of ATLAS to LLP decaying in the muon spectrometer in the first FLF part. Beyond this, I aim to extend my academic profile and continuing my work on ScanMu with international partners, exploring a new muon imaging concept.