Abstract
The future muon collider has the potential to discover feebly interacting particles in a wide range of masses above the electroweak scale. It is particularly suitable to search for heavy neutral leptons (HNLs), as their production cross section \( \sigma \sim {m}_W^{-2} \) is not suppressed by the new physics scale. We demonstrate that with the capacity to observe up to 105 events in the previously unexplored TeV mass range, the muon collider provides the means to measure the fraction of lepton number violating (LNV) processes with precision at the level of a percent. This capability enables elucidating the nature of HNLs, allowing us to differentiate between Majorana, Dirac, and non-minimal scenarios featuring multiple degenerate HNLs. We link the observed fraction of LNV processes to the parameters of the model with three degenerate HNLs, which could be responsible for generating baryon asymmetry in the Universe. Additionally, we present a simple estimate for the number of signal events, as well as analyze the feasibility of vector boson fusion processes in searches for HNLs.
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Acknowledgments
We thank Juraj Klaric for discussing the leptogenesis in the model of 3 HNLs and for proofreading the manuscript. The evaluation of the cross sections has been done with the use of FeynCalc [96, 97]. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (GA 694896), from the NWO Physics Vrij Programme “The Hidden Universe of Weakly Interacting Particles”, No. 680.92.18.03, which is partly financed by the Dutch Research Council NWO, and from the Den Adel Fund in the form of a scholarship.
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Mikulenko, O., Marinichenko, M. Measuring lepton number violation in heavy neutral lepton decays at the future muon collider. J. High Energ. Phys. 2024, 32 (2024). https://doi.org/10.1007/JHEP01(2024)032
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DOI: https://doi.org/10.1007/JHEP01(2024)032