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Characterizing dark bosons at Chiral Belle

Carlos Henrique de Lima ^1,*, David McKeen ^1,†, Afif Omar ^1,2,‡, and Douglas Tuckler ^1,3,§

¹TRIUMF, 4004 Wesbrook Mall, Vancouver, British Columbia V6T 2A3, Canada
²Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia V8P 5C2, Canada
³Department of Physics, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada

^*Contact author: cdelima@triumf.ca
^†Contact author: mckeen@triumf.ca
^‡Contact author: aomar@triumf.ca
^§Contact author: dtuckler@triumf.ca

Phys. Rev. D 112, 095025 – Published 18 November, 2025

DOI: https://doi.org/10.1103/6zpx-5tt1

Abstract

We explore the advantages of a polarized electron beam at Belle II, as proposed for “Chiral Belle,” in the search for invisibly decaying (dark) bosons that weakly couple to the Standard Model. By measuring the polarization dependence of the production cross section of dark bosons in association with a photon, the dark boson’s spin and Lorentz structure of its couplings can potentially be determined. We analyze the mono-photon channel $e^{+} e^{-} \to γ + invisible$ in detail, focusing on the production of an on-shell spin-1 boson. We explore this in the context of three separate scenarios for a new dark vector: a dark photon, a mass-mixed “dark $Z$ ,” and a vector that couples to right-handed electrons, and we estimate how well the couplings of such bosons to electrons can be constrained in the event of a positive signal.

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Phys. Rev. D 112, 095025– Published 18 November, 2025

Vol. 112, Iss. 9 — 1 November 2025

Received 2 August 2025
Accepted 29 October 2025

DOI: https://doi.org/10.1103/6zpx-5tt1

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.

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Characterizing dark bosons at Chiral Belle

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