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Observation of the Z →ψ + - Decay in pp Collisions at s =13 TeV

par Sirunyan, A.M.;Beghin, Diego ;Bilin, Bugra ;Brun, Hugues ;Clerbaux, Barbara ;De Lentdecker, Gilles ;Delannoy, Hugo ;Dorney, Brian ;Fasanella, Giuseppe ;Favart, Laurent ;Goldouzian, Reza ;Grebenyuk, Anastasia ;Kalsi, Amandeep Kaur ;Lenzi, Thomas ;Luetic, Jelena ;Postiau, Nicolas ;Starling, Elizabeth Rose ;Thomas, Laurent ;Vander Velde, Catherine ;Vanlaer, Pascal ;Vannerom, David ;Wang, Qun ; [et al.]
Référence Physical review letters, 121, 14, 141801
Publication Publié, 2018-10-04

Article révisé par les pairs

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Résumé :

This Letter presents the observation of the rare Z boson decay Z→ψ + -. Here, ψ represents contributions from direct J/ψ and ψ(2S)→J/ψX, + - is a pair of electrons or muons, and the J/ψ meson is detected via its decay to μ+μ-. The sample of proton-proton collision data, collected by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV, corresponds to an integrated luminosity of 35.9 fb-1. The signal is observed with a significance in excess of 5 standard deviations. After subtraction of the ψ(2S)→J/ψX contribution, the ratio of the branching fraction of the exclusive decay Z→J/ψ + - to the decay Z→μ+μ-μ+μ- within a fiducial phase space is measured to be B(Z→J/ψ + -)/B(Z→μ+μ-μ+μ-)=0.67±0.18(stat)±0.05(syst).