Observation of the Rare Decay of the η Meson to Four Muons

CMS Collaboration

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


A search for the rare Formula Presented 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 during 2017 and 2018 and corresponding to an integrated luminosity of Formula Presented. A signal having a statistical significance well in excess of 5 standard deviations is observed. Using the Formula Presented decay as normalization, the branching fraction Formula Presented is measured, where the last term is the uncertainty in the normalization channel branching fraction. This work achieves an improved precision of over 5 orders of magnitude compared to previous results, leading to the first measurement of this branching fraction, which is found to agree with theoretical predictions.

Original languageEnglish (US)
Article number091903
JournalPhysical review letters
Issue number9
StatePublished - Sep 1 2023

All Science Journal Classification (ASJC) codes

  • General Physics and Astronomy


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