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

The Standard Model of Elementary Particle Physics (SM) is the deepest, most
complete and accurate scientific theory and has passed decades of experimental
tests. 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 questions
predict new, electrically neutral particles with long lifetimes on the scale
that can be probed by typical collider experiments like ATLAS or CMS at the
Large Hadron Collider (LHC) of CERN. Yet, there is a striking gap in
sensitivity for such long-lived particles that are electrically neutral and
have a mass above 1 Gigaelectronvolt (GeV), i.e., are more massive than a
hydrogen atom. This sensitivity gap spans several orders of magnitude in the
lifetimes, which translates into decay lengths from 100 m and up to the
Big-Bang nucleosynthesis bound of 100,000,000 m, quite reasonably assuming the
particles move at the speed of light when produced at the LHC.

This proposal aims to close the present gap in sensitivity to long-lived
particles in a timely manner and at up to one order of magnitude lower costs
than proposals with competing sensitivity, resulting in a transformative impact
on the field. This can be achieved by instrumenting the existing service shafts
of the ATLAS experiment at the Large Hadron Collider (LHC) of CERN. The
foreseen detector structure, AN Underground Belayed In-Shaft search experiment
(ANUBIS), will consist of a number of tracking stations belayed into the shaft
and affixed to its walls, instrumenting approximately 15,000 m^3 with dedicated
tracking detectors with excellent timing capability. For scenarios with
electrically neutral long-lived particles with masses above 1 GeV, the lifetime
reach is increased by a factor of up to 1,000 compared to currently operating
and approved future experiments. To master this challenge cost-effectively,
the tracking stations of ANUBIS will employ the next generation of detectors
using the resistive plate chamber (RPC) technology that I will develop in the
proposed FLF project using the low-cost, large-scale specifications of ANUBIS.

In addition to the ambitious research programme above, another important
objective is to expand the full potential of the existing ATLAS detector to
search for long-lived particles on a short time scale.

The detector technology that I will develop in the proposed FLF project using
the low-cost, large-scale specifications of ANUBIS is an ideal candidate for
the scanning of buildings, bridges, and other large-scale infrastructure using
muon tomography based on naturally occurring cosmic rays. Cosmic ray tomography
provides crucial advantages over currently available approaches that suffer
from a limited depth reach and resolution (radar), are expensive and carry
significant health and safety risks (X-ray), or even prohibitive (destructive
methods). Preliminary research reveals a wide range of applications, given the
large number of ageing buildings and infrastructure constructed in the 1950-70s
with questionable structural integrity. The environmental human footprint can
be dramatically reduced by using existing structures for longer in a safe
manner, which, combined with substantial cost savings, will enormously benefit
our society. One of the main goals of the FLF proposal is to realise a
full-scale demonstrator prototype for cosmic ray tomography including field
tests, with an intermediate-term goal of commercialisation.