Abstract
We discuss the impact of heavy neutrino-antineutrino oscillations (\( \textrm{N}\overline{\textrm{N}}\textrm{Os} \)) on heavy neutral lepton (HNL) searches at proposed electron-positron colliders such as the future circular e+e− collider (FCC-ee). During the Z pole run, HNLs can be produced alongside a light neutrino or antineutrino that escapes detection and can decay into a charged lepton or antilepton together with an off-shell W boson. In this case, signals of lepton number violation (LNV) only show up in the final state distributions. We discuss how \( \textrm{N}\overline{\textrm{N}}\textrm{Os} \), a typical feature of collider-testable low-scale seesaw models where the heavy neutrinos form pseudo-Dirac pairs, modify such final state distributions. For example, the forward-backward asymmetry (FBA) of the reconstructed heavy (anti)neutrinos develops an oscillatory dependence on the HNL lifetime. We show that these oscillations can be resolvable for long-lived HNLs. We also discuss that when the \( \textrm{N}\overline{\textrm{N}}\textrm{Os} \) are not resolvable, they can nevertheless significantly modify the theory predictions for FBAs and observables such as the ratio of the total number of HNL decays into ℓ− over ones into ℓ+, in an interval of the angle θ between the HNL and the beam axis. Our results show that \( \textrm{N}\overline{\textrm{N}}\textrm{Os} \) should be included in collider simulations of HNLs at the FCC-ee.
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Acknowledgments
The work of Jan Hajer as partially supported by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) through the projects CFTP-FCT Unit UIDB/00777/2020, UIDP/00777/ 2020, CERN/FIS-PAR/0002/2021, and CERN/FIS-PAR/0019/2021, which are partially funded through POCTI (FEDER), COMPETE, QREN and the EU.
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Antusch, S., Hajer, J. & Oliveira, B.M.S. Heavy neutrino-antineutrino oscillations at the FCC-ee. J. High Energ. Phys. 2023, 129 (2023). https://doi.org/10.1007/JHEP10(2023)129
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DOI: https://doi.org/10.1007/JHEP10(2023)129