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Long-lived light mediators in a Higgs portal model at the FCC-ee

Biplob Bhattacherjee1,*, Camellia Bose1,†, Herbi K. Dreiner2,‡, Nivedita Ghosh3,§, Shigeki Matsumoto3,∥, and Rhitaja Sengupta2,¶

  • 1Centre for High Energy Physics, Indian Institute of Science, Bengaluru 560012, India
  • 2Bethe Center for Theoretical Physics and Physikalisches Institut der Universität Bonn, Nußallee 12, Bonn 53115, Germany
  • 3Kavli IPMU (WPI), UTIAS, University of Tokyo, Kashiwa, Chiba, 277-8583, Japan

  • *Contact author: biplob@iisc.ac.in
  • †Contact author: camelliabose@iisc.ac.in
  • ‡Contact author: dreiner@uni-bonn.de
  • §Contact author: nivedita.ghosh@ipmu.jp
  • ∥Contact author: shigeki.matsumoto@ipmu.jp
  • Contact author: rsengupt@uni-bonn.de
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Phys. Rev. D 113, 035022 – Published 20 February, 2026

DOI: https://doi.org/10.1103/t129-lzq4

Abstract

In the search for beyond the Standard Model (SM) physics, long-lived particles (LLPs) have emerged as potential candidates and are being explored in various ongoing experiments. Future lepton colliders, such as the FCC-ee, shall provide an excellent opportunity to probe LLPs, owing to their clean environment and improved particle identification. This study investigates the potential of the proposed Innovative Detector for an Electron-Positron Accelerator (IDEA) detector at FCC-ee in the detection of LLPs produced from B-meson and Higgs boson decays. We explore benchmark scenarios for different final states resulting from LLP decays, including a detailed analysis of the SM long-lived hadronic background. Additionally, we propose dedicated LLP detectors with different configurations, dimensions, and locations with respect to the IDEA detector. DELIGHT B, originally proposed as a dedicated LLP detector for the FCC-hh, stands out as the detector with the maximum efficiency for detecting LLPs produced at FCC-ee. We find that cylindrical detector configurations, if feasible to construct around the IDEA detector, would also enhance sensitivity for LLPs mostly decaying outside it.

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Phys. Rev. D 113, 035022– Published 20 February, 2026
  • Received 2 April 2025
  • Accepted 26 January 2026
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