Observation of the rare decay of the $\eta$ meson to four muons

Abstract

A search for the rare $\eta$ $\to$ ${\mu }^{+}{\mu }^{-}{\mu }^{+}{\mu }^{-}$ double-Dalitz decay is performed using a sample of proton-proton collisions, collected by the CMS experiment at the CERN LHC with high-rate muon triggers in 2017-2018 and corresponding to an integrated luminosity of 101 fb${}^{-1}$. A signal having a statistical significance well in excess of 5 standard deviations is observed. Using the $\eta$ $\to$ ${\mu }^{+}{\mu }^{-}$ decay as normalization, the branching fraction $\mathcal{B}(\eta$ $\to$ ${\mu }^{+}{\mu }^{-}{\mu }^{+}{\mu }^{-})$ = [5.0 $\pm$ 0.8 (stat) $\pm$ 0.7 (syst) $\pm$ 0.7 (${\mathcal{B}}_{2\mu }$)] $\times$ 10${}^{-9}$ is measured, where the last term is the uncertainty in the normalization channel branching fraction. This work achieves an improved precision of over five orders of magnitude compared to previous results, leading to the first measurement of this branching fraction, which is found to agree with theoretical predictions.

arXiv commentReplaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/BPH-22-003 (CMS Public Pages)

References in corpus (17)

• An Introduction to PYTHIA 8.2
• The CMS trigger system
• Description and performance of track and primary-vertex reconstruction with the CMS tracker
• Performance of the CMS muon detector and muon reconstruction with proton-proton collisions at $\sqrt{s}=$ 13 TeV
• Extraction and validation of a new set of CMS PYTHIA8 tunes from underlying-event measurements
• Precision luminosity measurement in proton-proton collisions at $\sqrt{s}=$ 13 TeV in 2015 and 2016 at CMS
• Electron and photon reconstruction and identification with the CMS experiment at the CERN LHC
• Search for narrow resonances in dijet final states at sqrt(s) = 8 TeV with the novel CMS technique of data scouting
• Scalar Meson Contributions to a_μfrom Hadronic Light-by-Light Scattering
• Precision tests of fundamental physics with $\eta$ and ${\eta }^{\prime }$ mesons
• Search for a narrow resonance lighter than 200 GeV decaying to a pair of muons in proton-proton collisions at $\sqrt{s}=$ 13 TeV
• The eta transition form factor from space- and time-like experimental data
• Measurement of eta meson decays into lepton-antilepton pairs
• eta, eta-prime --> pi+ pi- l+ l- in a chiral unitary approach
• A data-driven approach to ${\pi }^0,\eta$ and ${\eta }^{\prime }$ single and double Dalitz decays
• Observation of the rare eta->e+e-e+e- decay with the KLOE experiment
• Observation of the double Dalitz decay ${\eta }^{\prime }\to e^{+}{e}^{-}{e}^{+}{e}^{-}$

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