Gutsche, T., Hiller Blin, A. N., Kovalenko, S., Kuleshov, S., Lyubovitskij, V. E., & Vicente Vacas, M. J. (2017). CP-violating decays of the pseudoscalars eta and eta' and their connection to the electric dipole moment of the neutron. Phys. Rev. D, 95(3), 036022–9pp.
Abstract: Using the present upper bound on the neutron electric dipole moment, we give an estimate for the upper limit of the CP-violating couplings of the eta(eta') to the nucleon. Using this result, we then derive constraints on the CP-violating eta(eta')pi pi couplings, which define the two-pion CP-violating decays of the eta and eta' mesons. Our results are relevant for the running and planned measurements of rare decays of the. eta and eta' mesons by the GlueX Collaboration at JLab and the LHCb Collaboration at CERN.
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Gninenko, S. N., Krasnikov, N. V., Kuleshov, S., Lyubovitskij, V. E., Crivelli, P., Kirpichnikov, D. V., et al. (2026). Probing millicharged particles with NA64μ and LDMX. Eur. Phys. J. C, 86(2), 140–11pp.
Abstract: Millicharged particles emerge as compelling candidates in numerous theoretically well-motivated extensions of the Standard Model. These hypothetical particles, characterized by an electric charge that is a small fraction of the elementary charge, have attracted significant attention in contemporary experimental physics. Their potential existence motivates dedicated search strategies across multiple experimental platforms, leveraging their distinctive electromagnetic interactions while evading conventional detection methods. In the present paper we estimated the projected sensitivity of fixed-target experiments, specifically NA64 μand LDMX, to the parameter space of millicharged particles. For the NA64 μexperiment, with an anticipated muon flux of MOT < 10(14), our analysis reveals a detectable mass window of 10 MeV < m(chi) < 150 MeV and charge parameter range 10(-4) less than or similar to is an element of( )less than or similar to 7 x 10(-4). This sensitivity arises from the bremsstrahlung-like missing energy signature μN ->mu N gamma *(-> chi chi<overline>). Furthermore, we evaluate the discovery potential of the LDMX facility, considering its projected electron beam statistics, EOT less than or similar to 2 x 10(16), and energy, E-e similar or equal to 8 GeV. Our results demonstrate that LDMX can probe heavier MCPs in the mass range 250 MeV less than or similar to m(chi )less than or similar to 400 MeV, with sensitivities reaching 10(-3) less than or similar to is an element of( )less than or similar to 1.5 x 10(-3). This parametric window can be accessible through the distinctive invisible decay channel rho -> chi chi<overline>, where rho-meson photo-production gamma N-N rho plays a pivotal role.
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