@article{10902/32449,
year = {2023},
month = {9},
url = {https://hdl.handle.net/10902/32449},
abstract = {A search for the rare η → μ+μ−μ+μ− 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 101 fb−¹. A signal having a statistical significance well in excess of 5 standard deviations is observed. Using the η → μ+μ− decay as normalization, the branching fraction B(η → μ+μ−μ+μ−) = [5.0 ± 0.8(stat) ± 0.7(syst) ± 0.7(β₂μ)] × 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 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.},
publisher = {American Physical Society},
publisher = {Physical Review Letters, 2023, 131(9), 091903},
title = {Observation of the Rare Decay of the n Meson to Four Muons},
author = {Hayrapetyan, A. and Blanco Fernández, Sergio and Brochero Cifuentes, Javier Andrés and Cabrillo Bartolomé, José Iban and Calderón Tazón, Alicia and Duarte Campderros, Jorge and Fernández García, Marcos and Fernández Madrazo, Celia and Gómez Gramuglio, Gervasio and Lasaosa García, Clara and Martínez Rivero, Celso and Martínez Ruiz del Árbol, Pablo and Matorras Weinig, Francisco and Matorras Cuevas, Pablo and Navarrete Ramos, Efrén and Piedra Gómez, Jonatan and Prieëls, Cedric and Scodellaro, Luca and Vila Álvarez, Iván  and Vizán García, Jesús Manuel},
}