Observation of the rare decay $η$ $\to$ $μ^+μ^-$e$^+$e$^-$
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arXiv
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| Natura: | Preprint |
| Pubblicazione: |
2026
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| _version_ | 1866910183673823232 |
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| author | CMS Collaboration |
| author_facet | CMS Collaboration |
| contents | A first observation of the rare decay $η$ $\to$ $μ^+μ^-$e$^+$e$^-$ is reported by the CMS Collaboration at the CERN LHC. The result is based on a proton-proton collision data sample at $\sqrt{s}$ = 13.6 TeV corresponding to an integrated luminosity of 38.0 fb$^{-1}$, acquired in 2022 using a high-rate dimuon trigger. Using the $η$ $\to$ $μ^+μ^-γ$ decay channel for normalization, the branching fraction is measured to be $\mathcal{B}$($η$ $\to$ $μ^+μ^-$e$^+$e$^-$) = (2.4 $\pm$ 0.8)$\times$ 10$^{-6}$, with the uncertainty including statistical and systematic sources as well as the $\mathcal{B}$($η$ $\to$ $μ^+μ^-γ$) uncertainty. This result is close to two orders of magnitude smaller than the existing limit, and is consistent with recent theoretical predictions. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_00615 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Observation of the rare decay $η$ $\to$ $μ^+μ^-$e$^+$e$^-$ CMS Collaboration High Energy Physics - Experiment A first observation of the rare decay $η$ $\to$ $μ^+μ^-$e$^+$e$^-$ is reported by the CMS Collaboration at the CERN LHC. The result is based on a proton-proton collision data sample at $\sqrt{s}$ = 13.6 TeV corresponding to an integrated luminosity of 38.0 fb$^{-1}$, acquired in 2022 using a high-rate dimuon trigger. Using the $η$ $\to$ $μ^+μ^-γ$ decay channel for normalization, the branching fraction is measured to be $\mathcal{B}$($η$ $\to$ $μ^+μ^-$e$^+$e$^-$) = (2.4 $\pm$ 0.8)$\times$ 10$^{-6}$, with the uncertainty including statistical and systematic sources as well as the $\mathcal{B}$($η$ $\to$ $μ^+μ^-γ$) uncertainty. This result is close to two orders of magnitude smaller than the existing limit, and is consistent with recent theoretical predictions. |
| title | Observation of the rare decay $η$ $\to$ $μ^+μ^-$e$^+$e$^-$ |
| topic | High Energy Physics - Experiment |
| url | https://arxiv.org/abs/2605.00615 |