Search for an Lμ − Lτ gauge boson using Z → 4μ events in proton-proton collisions at √s=13 TeV
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AuthorSirunyan, A. M.; Cabrillo Bartolomé, José Iban; Calderón Tazón, Alicia; Chazín Quero, Bárbara; Duarte Campderros, Jorge; Fernández García, Marcos; Fernández Manteca, Pedro José; García Alonso, Andrea; García Ferrero, Juan; Gómez Gramuglio, Gervasio; López Virto, María Amparo; Marco de Lucas, Jesús; Martínez Rivero, Celso; Martínez Ruiz de Árbol, Pablo; Matorras Weinig, Francisco; Piedra Gómez, Jonatan; Prieels, Cedric Gerald; Rodrigo Anoro, Teresa; Ruiz Jimeno, Alberto; [et al.]
A search for a narrow Z′ gauge boson with a mass between 5 and 70 GeV resulting from an Lμ−Lτ U(1) local gauge symmetry is reported. Theories that predict such a particle have been proposed as an explanation of various experimental discrepancies, including the lack of a dark matter signal in direct-detection experiments, tension in the measurement of the anomalous magnetic moment of the muon, and reports of possible lepton flavor universality violation in B meson decays. A data sample of proton-proton collisions at a center-of-mass energy of 13 TeV is used, corresponding to an integrated luminosity of 77.3 fb−1 recorded in 2016 and 2017 by the CMS detector at the LHC. Events containing four muons with an invariant mass near the standard model Z boson mass are analyzed, and the selection is further optimized to be sensitive to the events that may contain Z→Z′μμ→4μ decays. The event yields are consistent with the standard model predictions. Upper limits of 10−8–10−7 at 95% confidence level are set on the product of branching fractions B(Z→Z′μμ)B(Z′→μμ), depending on the Z′ mass, which excludes a Z′ boson coupling strength to muons above 0.004–0.3. These are the first dedicated limits on Lμ−Lτ models at the LHC and result in a significant increase in the excluded model parameter space. The results of this search may also be used to constrain the coupling strength of any light Z′ gauge boson to muons.
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