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ANUBIS: Projected Sensitivities and Initial Results from the proANUBIS demonstrator with Run 3 LHC data

Théo Reymermier, Oleg Brandt, Anna Mullin, Paul Swallow, Michael Revering, Cayetano Fernandez Ruiz

TL;DR

This work assesses the projected sensitivities of the proposed ANUBIS detector to neutral long-lived particles and reports first results from the proANUBIS prototype in the ATLAS cavern. It formalizes LLP phenomenology with two benchmarks—a Higgs-portal scalar and a Heavy Neutral Lepton—and introduces SET-ANUBIS, a framework for rapid sensitivity studies using UFO models and event generators. The results show that ANUBIS can probe LLP lifetimes from about $1\,\mathrm{m}$ to $10^5\,\mathrm{m}$ for Higgs-portal scenarios and from $0.1$ to $10^3\,\mathrm{m}$ for HNLs, offering complementary coverage to prompt ATLAS searches and other far-detector proposals. The proANUBIS demonstration confirms synchronization with ATLAS and provides real-background estimation to guide future background-reduction strategies and model extensions, laying the groundwork for expanded sensitivity studies across additional dark-sector scenarios.

Abstract

Despite the success of the Standard Model (SM) there remains behaviour it cannot describe, in particular the presence of non-interacting Dark Matter. Many models that describe dark matter can generically introduce exotic Long-Lived Particles (LLPs). The proposed ANUBIS experiment is designed to search for these LLPs within the ATLAS detector cavern, located approximately 20-30 m from the Interaction Point (IP). A prototype detector, proANUBIS, has taken data within the ATLAS detector cavern since 2024, corresponding to 104 $fb^{-1}$ of pp data. We report on the potential sensitivity of ANUBIS to a selection of LLP models, i.e. Higgs Portal and Heavy Neutral Leptons, as well as future planned studies. Additionally, we will show the first results of the proANUBIS demonstrator, and how it will be used to study the expected backgrounds for the ANUBIS detector.

ANUBIS: Projected Sensitivities and Initial Results from the proANUBIS demonstrator with Run 3 LHC data

TL;DR

This work assesses the projected sensitivities of the proposed ANUBIS detector to neutral long-lived particles and reports first results from the proANUBIS prototype in the ATLAS cavern. It formalizes LLP phenomenology with two benchmarks—a Higgs-portal scalar and a Heavy Neutral Lepton—and introduces SET-ANUBIS, a framework for rapid sensitivity studies using UFO models and event generators. The results show that ANUBIS can probe LLP lifetimes from about to for Higgs-portal scenarios and from to for HNLs, offering complementary coverage to prompt ATLAS searches and other far-detector proposals. The proANUBIS demonstration confirms synchronization with ATLAS and provides real-background estimation to guide future background-reduction strategies and model extensions, laying the groundwork for expanded sensitivity studies across additional dark-sector scenarios.

Abstract

Despite the success of the Standard Model (SM) there remains behaviour it cannot describe, in particular the presence of non-interacting Dark Matter. Many models that describe dark matter can generically introduce exotic Long-Lived Particles (LLPs). The proposed ANUBIS experiment is designed to search for these LLPs within the ATLAS detector cavern, located approximately 20-30 m from the Interaction Point (IP). A prototype detector, proANUBIS, has taken data within the ATLAS detector cavern since 2024, corresponding to 104 of pp data. We report on the potential sensitivity of ANUBIS to a selection of LLP models, i.e. Higgs Portal and Heavy Neutral Leptons, as well as future planned studies. Additionally, we will show the first results of the proANUBIS demonstrator, and how it will be used to study the expected backgrounds for the ANUBIS detector.

Paper Structure

This paper contains 14 sections, 9 equations, 5 figures.

Table of Contents

  1. Introduction
  2. LLP phenomenology and benchmark models
  3. Generic LLP kinematics
  4. Higgs portal
  5. Heavy Neutral Lepton (HNL)
  6. ANUBIS detector and proANUBIS
  7. ANUBIS detector concept
  8. proANUBIS demonstrator
  9. Ongoing data analyses
  10. Framework, analysis strategy and datasets
  11. Results
  12. Higgs-portal scalar limits
  13. HNL limits
  14. Conclusion

Figures (5)

  • Figure 1: Example of tracks and vertex reconstruction using data from proANUBIS.
  • Figure 2: Heatmap of muons in synchronized events, detected by ATLAS and ANUBIS.
  • Figure 3: General architecture of SET-ANUBIS.
  • Figure 4: Projected Higgs-portal scalar exclusions for ANUBIS.
  • Figure 5: Projected 95% CL exclusions in the $(m_N,|U_\ell|^2)$ plane for $N_e$ and $N_\mu$.