This Letter presents the observation of the rare Z boson decay Z→ψℓ^+ℓ^-. Here, ψ represents contributions from direct J/ψ and ψ(2S)→J/ψX, ℓ^+ℓ^- 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/ψℓ^+ℓ^- to the decay Z→μ^+μ^-μ^+μ^- within a fiducial phase space is measured to be B(Z→J/ψℓ^+ℓ^-)/B(Z→μ^+μ^-μ^+μ^-)=0.67±0.18(stat)±0.05(syst).
Observation of the Z→ψℓ^+ℓ^- Decay in pp Collisions at sqrt[s]=13 TeV
Albergo, S;Potenza, R;Tricomi, A;Tuve, C;
2018-01-01
Abstract
This Letter presents the observation of the rare Z boson decay Z→ψℓ^+ℓ^-. Here, ψ represents contributions from direct J/ψ and ψ(2S)→J/ψX, ℓ^+ℓ^- 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/ψℓ^+ℓ^- to the decay Z→μ^+μ^-μ^+μ^- within a fiducial phase space is measured to be B(Z→J/ψℓ^+ℓ^-)/B(Z→μ^+μ^-μ^+μ^-)=0.67±0.18(stat)±0.05(syst).File | Dimensione | Formato | |
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PhysRevLett.121.141801.pdf
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