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Searching for long-lived particles at the LHC

Cristiano Alpigiani, University of Washington
Tuesday, April 4, 2023 - 4:30pm
PAT C-421

Many extensions of the Standard Model include particles that are weakly coupled and long-lived that can decay to final states containing hadronic jets and leptons. Long-lived particles can be detected as displaced decays from the interaction point or missing energy if they escape.

When produced, the long-lived particles can decay far from the interaction vertex of the primary proton–proton collision. Long-lived particle signatures are distinct from those of promptly decaying particles that are targeted by the majority of searches for new physics at the LHC. Given their non-standard nature, these searches require customized reconstruction algorithms, very peculiar trigger selections, and robust background rejection. I will present the latest results on the searches for long-lived particles at the LHC by the ATLAS, CMS, and LHCb experiments.

However, the current searches performed at colliders have some limitations. Unfortunately, no existing or proposed search strategy will be able to observe the decay of non-hadronic electrically neutral LLPs with masses above ~ GeV and lifetimes near the limit set by Big Bang Nucleosynthesis (cτ 107-108 m). Therefore, ultra-long-lived particles (ULLPs) produced at the LHC will escape the main detector with an extremely high probability. I will also review the new detector proposals that could extend the sensitivity to longer lifetimes.

Cristiano Alpigiani completed his Ph.D. in Physics at Queen Mary University of London, London, UK, on a Search for rare B decays into two muons with the ATLAS detector and joined the EPE group as a post doc working on searches of long-lived particles in pp collisions in the ATLAS detector. He has been a major contributor to the EPE Long-lived particle searches. He has significantly contributed ATLAS Luminosity measurements, ITk tracking efficiencies and resolutions studies. He made major contribution to the MATHUSLA test stand setup at CERN (services installation, assembling, transport, commissioning, and data taking, RPC detectors testing, design of the supporting structure). He has served as the convener of the ATLAS Non-Collision Background studies. He is currently a Research Scientist with the EPE group.

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