Department of Physics & Astronomy
University of New Mexico

Nuclear, Particle, Astroparticle and Cosmology (NUPAC) Seminars

Search for Neutral Long-lived Particles Decaying in the CMS Endcap Muon Detectors

Presented by Christina Wang, Caltech

Many extensions of the standard model (SM) predict the existence of neutral, weakly-coupled particles that have a long lifetime. These long-lived particles (LLPs) often provide striking displaced signatures in detectors, thus escaping the conventional searches for prompt particles and remaining largely unexplored at the LHC. I will present a first search at the LHC that uses a muon detector as a sampling calorimeter to identify displaced showers produced by decays of LLPs. The search is sensitive
to LLPs decaying to final states including hadrons, taus, electrons, or photon, LLP masses as low as a few GeV, and is largely model-independent. The search is enabled by the unique design of CMS endcap muon detectors (EMD), composed of detector planes interleaved
with the steel layers of the magnet flux-return yoke. Decays of LLPs in the EMD induce hadronic and electromagnetic showers, giving rise to a high hit multiplicity in localized detector regions that can be efficiently identified with a novel reconstruction technique. The steel flux-return yoke in the CMS detector also provides exceptional shielding from the SM background that dominates existing LLP searches. The search yields competitive sensitivity for proper lifetime from 0.1m to 1000m with the full Run2 dataset recorded at the LHC. I will also discuss the supplementary materials and HEPData entry provided for the analysis that would allow reinterpretation of the analysis to any models that contain LLPs.

2:00 pm, Tuesday, October 19, 2021

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