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  • Open Access

Detector performance at SHiP for cascade-produced long-lived particles

Matei Climescu1,*, Yehor Kyselov2,†, and Maksym Ovchynnikov3,‡

  • *Contact author: matei.climescu@cern.ch
  • †Contact author: kiselev883@gmail.com
  • ‡Contact author: maksym.ovchynnikov@cern.ch
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Phys. Rev. D 114, 056016 – Published 14 September, 2026

DOI: https://doi.org/10.1103/h9gk-mjjh

Abstract

Previous studies have shown that cascade production in the thick target of the Search for Hidden Particles (SHiP) experiment may substantially enhance the number of light long-lived particles (LLPs) decaying in the fiducial volume. However, cascade-produced LLPs are typically soft, so daughter-level acceptance and reconstruction effects can strongly suppress the observable event rate. We quantify this suppression for two representative cases: photophilic axionlike particles (ALPs) produced in electromagnetic cascades and heavy neutral leptons (HNLs) produced in decays of secondary kaons. We combine a semianalytic event-rate calculation with a detector-level study of ALP reconstruction in the electromagnetic calorimeter. For the nominal SHiP detector design, cascade ALPs give at most a moderate enhancement over primary production and only at the lightest masses; at higher masses, the cascade contribution becomes subdominant or negligible. For HNLs from secondary kaons, the cascade contribution is already subdominant after imposing daughter-level geometric acceptance. We also identify possible ways to recover part of the cascade event rate, including relaxed event-selection criteria and an active decay-volume subdetector.

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Phys. Rev. D 114, 056016– Published 14 September, 2026
  • Received 12 June 2026
  • Accepted 24 August 2026
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