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Searching for long-lived particles in free neutron experiments

Meirose, B. LU orcid ; Nieuwenhuis, R. LU ; Pasechnik, R. LU ; Gisbert, H. ; Vale Silva, L. and Milstead, D. (2025) In Journal of Physics G: Nuclear and Particle Physics 52(7).
Abstract

We explore the decay of free neutrons into exotic long-lived particles, whose decays could be detected in the next-generation free neutron experiments. We show that such a possibility is viable as long as the exotic particle is highly mass-degenerate with the neutron, avoiding exclusion by large-volume detectors. We estimate the number of observable events and identify the most promising final states from both theoretical and experimental perspectives. Our analysis highlights the unique capability of the HIBEAM-NNBAR experiment at the European spallation source to probe this unexplored region of parameter space, opening a new avenue for exploring physics beyond the Standard Model. We estimate that several events per year could be... (More)

We explore the decay of free neutrons into exotic long-lived particles, whose decays could be detected in the next-generation free neutron experiments. We show that such a possibility is viable as long as the exotic particle is highly mass-degenerate with the neutron, avoiding exclusion by large-volume detectors. We estimate the number of observable events and identify the most promising final states from both theoretical and experimental perspectives. Our analysis highlights the unique capability of the HIBEAM-NNBAR experiment at the European spallation source to probe this unexplored region of parameter space, opening a new avenue for exploring physics beyond the Standard Model. We estimate that several events per year could be observed in the NNBAR experiment.

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author
; ; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
baryon number violation, European Spallation Source, free neutrons, long-lived particles, neutron lifetime, rare decays
in
Journal of Physics G: Nuclear and Particle Physics
volume
52
issue
7
article number
075001
publisher
IOP Publishing
external identifiers
  • scopus:105010589926
ISSN
0954-3899
DOI
10.1088/1361-6471/ade3f2
language
English
LU publication?
yes
additional info
Publisher Copyright: © 2025 The Author(s). Published by IOP Publishing Ltd.
id
ac14f674-e35c-48fa-9516-fc592242bab5
date added to LUP
2025-12-02 16:59:49
date last changed
2025-12-02 16:59:49
@article{ac14f674-e35c-48fa-9516-fc592242bab5,
  abstract     = {{<p>We explore the decay of free neutrons into exotic long-lived particles, whose decays could be detected in the next-generation free neutron experiments. We show that such a possibility is viable as long as the exotic particle is highly mass-degenerate with the neutron, avoiding exclusion by large-volume detectors. We estimate the number of observable events and identify the most promising final states from both theoretical and experimental perspectives. Our analysis highlights the unique capability of the HIBEAM-NNBAR experiment at the European spallation source to probe this unexplored region of parameter space, opening a new avenue for exploring physics beyond the Standard Model. We estimate that several events per year could be observed in the NNBAR experiment.</p>}},
  author       = {{Meirose, B. and Nieuwenhuis, R. and Pasechnik, R. and Gisbert, H. and Vale Silva, L. and Milstead, D.}},
  issn         = {{0954-3899}},
  keywords     = {{baryon number violation; European Spallation Source; free neutrons; long-lived particles; neutron lifetime; rare decays}},
  language     = {{eng}},
  month        = {{07}},
  number       = {{7}},
  publisher    = {{IOP Publishing}},
  series       = {{Journal of Physics G: Nuclear and Particle Physics}},
  title        = {{Searching for long-lived particles in free neutron experiments}},
  url          = {{http://dx.doi.org/10.1088/1361-6471/ade3f2}},
  doi          = {{10.1088/1361-6471/ade3f2}},
  volume       = {{52}},
  year         = {{2025}},
}