Speaker
Description
Many beyond the Standard Model (BSM) theories, such as hidden sector models, heavy neutral leptons, and neutral naturalness frameworks, predict invisible long-lived particles that travel macroscopic distances before decaying into visible Standard Model particles with a common spatial origin. Fast and accurate reconstruction of secondary vertices therefore plays a central role in ATLAS LLP searches. While significant advancements have been made in efficiently reconstructing Inner Detector tracks originating far from the primary Interaction Point (IP), traditional secondary vertexing algorithms still remain limited by the ID track reconstruction acceptance, significantly reducing sensitivity to LLP phase space where the bulk of expected decays lie beyond the Pixel detector. To address this limitation, we introduce a novel secondary vertexing technique that leverages StandAlone muon tracks reconstructed exclusively in the Muon Spectrometer, which demonstrates the ability to efficiently reconstruct ultra-displaced dimuon vertices up to 8 meters from the IP. This approach provides sensitivity to LLP decays occurring well beyond the Inner Detector, unlocking previously inaccessible phase-space for ATLAS LLP searches. In this presentation, we will discuss the implementation of the algorithm and performance of this technique on simulated LLP signatures, demonstrate its robustness against backgrounds, and explore its potential impact on future LLP searches in ATLAS.
