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Introduction

The particle nature of Dark Matter, which accounts for 4/5 of the Universe, is one of the biggest questions in physics today. Many extensions of the Standard Model with Dark Matter candidates also predict other new particles with macroscopic lifetimes. The Large Hadron Collider (LHC) provides an unprecedented possibility to search for such long-lived particles in a controlled laboratory environment.

Due to their finite size, it is difficult for existing LHC detectors like ATLAS to search for electrically neutral massive ultra-long-lived particles with proper lifetimes cτ > 10 m. To address this shortcoming, we recently proposed ANUBIS, AN Underground Belayed In-Shaft search experiment (see arXiv:1909.13022). The ANUBIS concept foresees instrumenting the existing service shafts above the ATLAS (or CMS) experiment with tracking stations, see sketch below.

ANUBIS detector concept

For scenarios with electrically neutral ultra-long-lived massive particles with masses of 1 GeV and above, the lifetime reach is increased by 2-3 orders of magnitude compared to currently operating and approved future experiments at the LHC, see Figure below for a standard benchmark model that assumes the Higgs boson as a portal beteween the Standard Model and the Dark Sector that contains the Dark Matter particle.

ANUBIS sensitivity

ANUBIS Detector Concept

The crux of the ANUBIS proposal is that it can provide a competitive sensitivity for very moderate costs. One important factor to achieve this is to rely on existing infrastructure, practically avoiding any need for civil engineering, for instance by "recycling" the PX14 service shaft of ATLAS and the existing infrastructure (for instance the crane, that can carry up to 270 t).

ANUBIS shaft

An important challenge for the costs of the ANUBIS detector is the sheer active area to be instrumented. We identified the Resistive Plate Chamber (RPC) technology as the best fit for purpose. This technology fulfills the strict timing requirements of below 500 ps, a good spatial resolution of about 1 cm, and all this for very moderate costs! In fact, the costs can be dramatically reduced by adapting the new generation of BIS7/8 RPCs being installed in ATLAS for Run 3, resulting (only!) a four-digit pricetag per square metre. Costs will be further reduced through a modular design of the detector.

ANUBIS concept

Current efforts

The efforts currently focus on further refining the strong physics case for ANUBIS and to explore Run 3 opportunities, as outlined below.

Detalied simulation of ANUBIS

We are currently working on a more detailed simulation of the ANUBIS detector. After an initial round of studies of the basic ANUBIS detector geometry (see proposal, first presentation at Physics Beyond Colliders, and recent talk at the VIIIth LLP workshop), we are aiming to further refine the ANUBIS detector geometry using MC simulations. Here, we focus on both SM processes and on other New Physics scenarios, using basic detector geometries. The imperative next step is to implement a full Geant4 based model of the ANUBIS detector, together with the PX14 shaft, the ATLAS cavern, and the ATLAS detector. This will help to leverage the ANUBIS geometry optimisation studies to the next level. Finally, we are working on the validation and performance studies of the BIS-7/8 PRCs, which use a very similar technology to that foreseen for ANUBIS, using MC simulations.

The proANUBIS prototype

An important component of any simulations of zero-background (or very low background) searches is to juxtapose the projections based on simulation with measurements. For this, we foresee constructing proANUBIS, a 1 x 1 x 1 m3 prototype of one tracking station unit module for ANUBIS based on BIS-7/8 RPC technology or possibly a Phase II upgrade technology, as shown in the sketch below. The primary goal of one proANUBIS prototype is to measure the particle fluxes in various positions inside the ATLAS cavern during Run 3 of the LHC and to study the performance in detail. Here, the focus is on the detector occupancy rate due to cavern background radiation and a solid trigger rate estimate. The ultimate goal is to correlate the measurements with the results from simulations elaborated above. Another proANUBIS prototype will be used for general performance studies, and to confirm the long-term stability of the detector response and radiation hardness when using eco-gases.

proANUBIS

Further information

Further information on ANUBIS can be found below, ranging from phenomenology/sensitivity studies performed by other groups, to (selected) presentations on ANUBIS at workshops and seminars.

ANUBIS on arXiv

There are several phenomenology/sensitivity studies involving ANUBIS that were performed by other groups:

Our ANUBIS proposal has also stimulated further work on future colliders:

Presentations on ANUBIS

Selected presentations on ANUBIS at workshops and seminars are provided below:

Selected seminar talks at:

ANUBIS Web Utilities

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Topic revision: r12 - 2021-01-22 - PeterJones
 
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