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Search for an Invisibly Decaying Z Boson at Belle II in e+eμ+μ(e±μ) Plus Missing Energy Final States

I. Adachi et al. (Belle II Collaboration)
Phys. Rev. Lett. 124, 141801 – Published 6 April 2020
Physics logo See synopsis: Closing in on the Z Boson
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Abstract

Theories beyond the standard model often predict the existence of an additional neutral boson, the Z. Using data collected by the Belle II experiment during 2018 at the SuperKEKB collider, we perform the first searches for the invisible decay of a Z in the process e+eμ+μZ and of a lepton-flavor-violating Z in e+ee±μZ. We do not find any excess of events and set 90% credibility level upper limits on the cross sections of these processes. We translate the former, in the framework of an LμLτ theory, into upper limits on the Z coupling constant at the level of 5×1021 for MZ6GeV/c2.

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  • Received 24 December 2019
  • Accepted 24 February 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.141801

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Particles & Fields

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Closing in on the Z Boson

Published 6 April 2020

The Belle II experiment finds no Z boson in its first results, but it does constrain how strongly the particle might interact with standard model particles.

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Vol. 124, Iss. 14 — 10 April 2020

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