Search for an Lμ − Lτ gauge boson using Z → 4μ events in proton-proton collisions at s=13 TeV

The CMS Collaboration

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82 Citations (Scopus)


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→Zμμ→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→Zμμ)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.

Original languageEnglish
Pages (from-to)345-368
Number of pages24
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
Publication statusPublished - 2019 May 10

Bibliographical note

Publisher Copyright:
© 2019 The Author(s)


  • CMS
  • Muons
  • Physics
  • Zprime

ASJC Scopus subject areas

  • Nuclear and High Energy Physics


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