Observation of the rare decay η → μ⁺μ^-e⁺e^-

2026/05/01 by CMS Collaboration · 1 voice
Physics and Astronomy · #hep-ex

paper · pdf

Abstract

A first observation of the rare decay η → μ⁺μ^-e⁺e^- is reported by the CMS Collaboration at the CERN LHC. The result is based on a proton-proton collision data sample at √(s) = 13.6 TeV corresponding to an integrated luminosity of 38.0 fb^-1, acquired in 2022 using a high-rate dimuon trigger. Using the η → μ⁺μ^-γ decay channel for normalization, the branching fraction is measured to be B(η → μ⁺μ^-e⁺e^-) = (2.4 ± 0.8)× 10^-6, with the uncertainty including statistical and systematic sources as well as the B(η → μ⁺μ^-γ) uncertainty. This result is close to two orders of magnitude smaller than the existing limit, and is consistent with recent theoretical predictions.

Citations

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Discussions

• #CMSpaper: Observation of the rare decay η → μ⁺μ⁻e⁺e⁻ (arXiv:2605.00615) https://arxiv.org/abs/2605.00615 #BPhysics [bsky, 1 points, 0 comments]