The Lμ-Lτ extension of the standard model predicts the existence of a lepton-flavor-universality-violating Z' boson that couples only to the heavier lepton families. We search for such a Z' through its invisible decay in the process e+e-→μ+μ-Z'. We use a sample of electron-positron collisions at a center-of-mass energy of 10.58 GeV collected by the Belle II experiment in 2019-2020, corresponding to an integrated luminosity of 79.7 fb^-1. We find no excess over the expected standard-model background. We set 90%-confidence-level upper limits on the cross section for this process as well as on the coupling of the model, which ranges from 3×10^-3 at low Z' masses to 1 at Z' masses of 8 GeV/c2.
Search for an Invisible Z' in a Final State with Two Muons and Missing Energy at Belle II
Bettarini, S;Casarosa, G;Corona, L;Forti, F;Massaccesi, L;Paoloni, E;Rizzo, G;Tenchini, F;
2023-01-01
Abstract
The Lμ-Lτ extension of the standard model predicts the existence of a lepton-flavor-universality-violating Z' boson that couples only to the heavier lepton families. We search for such a Z' through its invisible decay in the process e+e-→μ+μ-Z'. We use a sample of electron-positron collisions at a center-of-mass energy of 10.58 GeV collected by the Belle II experiment in 2019-2020, corresponding to an integrated luminosity of 79.7 fb^-1. We find no excess over the expected standard-model background. We set 90%-confidence-level upper limits on the cross section for this process as well as on the coupling of the model, which ranges from 3×10^-3 at low Z' masses to 1 at Z' masses of 8 GeV/c2.| File | Dimensione | Formato | |
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PhysRevLett.130.231801.pdf
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