Search for a ${\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ Resonance in ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}{\ensuremath{\tau}}^{+}{\ensuremath{\tau}}^{\ensuremath{-}}$ Events with the Belle II Experiment

Open Access

Search for a $τ^{+} τ^{-}$ Resonance in $e^{+} e^{-} \to μ^{+} μ^{-} τ^{+} τ^{-}$ Events with the Belle II Experiment

I. Adachi et al. (Belle II Collaboration)

Phys. Rev. Lett. 131, 121802 – Published 21 September 2023

Abstract

We report the first search for a nonstandard-model resonance decaying into $τ$ pairs in $e^{+} e^{-} \to μ^{+} μ^{-} τ^{+} τ^{-}$ events in the $3.6 - 10 GeV / c^{2}$ mass range. We use a $62.8 {fb}^{- 1}$ sample of $e^{+} e^{-}$ collisions collected at a center-of-mass energy of 10.58 GeV by the Belle II experiment at the SuperKEKB collider. The analysis probes three different models predicting a spin-1 particle coupling only to the heavier lepton families, a Higgs-like spin-0 particle that couples preferentially to charged leptons (leptophilic scalar), and an axionlike particle, respectively. We observe no evidence for a signal and set exclusion limits at 90% confidence level on the product of cross section and branching fraction into $τ$ pairs, ranging from 0.7 to 24 fb, and on the couplings of these processes. We obtain world-leading constraints on the couplings for the leptophilic scalar model for masses above $6.5 GeV / c^{2}$ and for the axionlike particle model over the entire mass range.

Received 22 June 2023
Accepted 8 August 2023

DOI:https://doi.org/10.1103/PhysRevLett.131.121802

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