AN Underground Belayed In-Shaft experiment to search for long-lived particles using LHC service shafts at CERN

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The Standard Model of Elementary Particle Physics (SM) is the deepest, mostcomplete and accurate scientific theory and has passed decades of experimentaltests. Yet, it cannot answer many fundamental questions. These include:- the nature of Dark Matter, which contributes 80% of the total mass in the Universe, - the puzzle of neutrino particles from e.g. nuclear reactions that are predicted to be massless by the SM but are experimentally known to have a very small albeit non-zero mass, and - the riddle of the origin of the matter-antimatter asymmetry that would explain why the Universe -- as we know it -- is composed of matter rather than antimatter,- etc.Many proposed theoretical scenarios that address these fundamental questionspredict new, electrically neutral particles with long lifetimes on the scalethat can be probed by typical collider experiments like ATLAS or CMS at theLarge Hadron Collider (LHC) of CERN. Yet, there is a striking gap insensitivity for such long-lived particles that are electrically neutral andhave a mass above 1 Gigaelectronvolt (GeV), i.e., are more massive than ahydrogen atom. This sensitivity gap spans several orders of magnitude in thelifetimes, which translates into decay lengths from 100 m and up to theBig-Bang nucleosynthesis bound of 100,000,000 m, quite reasonably assuming theparticles move at the speed of light when produced at the LHC.This proposal aims to close the present gap in sensitivity to long-livedparticles in a timely manner and at up to one order of magnitude lower coststhan proposals with competing sensitivity, resulting in a transformative impacton the field. This can be achieved by instrumenting the existing service shaftsof the ATLAS experiment at the Large Hadron Collider (LHC) of CERN. Theforeseen detector structure, AN Underground Belayed In-Shaft search experiment(ANUBIS), will consist of a number of tracking stations belayed into the shaftand affixed to its walls, instrumenting approximately 15,000 m^3 with dedicatedtracking detectors with excellent timing capability. For scenarios withelectrically neutral long-lived particles with masses above 1 GeV, the lifetimereach is increased by a factor of up to 1,000 compared to currently operatingand approved future experiments. To master this challenge cost-effectively,the tracking stations of ANUBIS will employ the next generation of detectorsusing the resistive plate chamber (RPC) technology that I will develop in theproposed FLF project using the low-cost, large-scale specifications of ANUBIS. In addition to the ambitious research programme above, another importantobjective is to expand the full potential of the existing ATLAS detector tosearch for long-lived particles on a short time scale. The detector technology that I will develop in the proposed FLF project usingthe low-cost, large-scale specifications of ANUBIS is an ideal candidate forthe scanning of buildings, bridges, and other large-scale infrastructure usingmuon tomography based on naturally occurring cosmic rays. Cosmic ray tomographyprovides crucial advantages over currently available approaches that sufferfrom a limited depth reach and resolution (radar), are expensive and carrysignificant health and safety risks (X-ray), or even prohibitive (destructivemethods). Preliminary research reveals a wide range of applications, given thelarge number of ageing buildings and infrastructure constructed in the 1950-70swith questionable structural integrity. The environmental human footprint canbe dramatically reduced by using existing structures for longer in a safemanner, which, combined with substantial cost savings, will enormously benefitour society. One of the main goals of the FLF proposal is to realise afull-scale demonstrator prototype for cosmic ray tomography including fieldtests, with an intermediate-term goal of commercialisation.