Search for a $\tau^+\tau^-$ resonance in $e^{+}e^{-}\rightarrow \mu^{+}\mu^{-} 
\tau^+\tau^-$ events with the Belle II experiment

The Belle-II Collaboration,; Adachi, I.; et al.,

doi:10.1103/PhysRevLett.131.121802

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Search for a $\tau^+\tau^-$ resonance in $e^{+}e^{-}\rightarrow \mu^{+}\mu^{-} \tau^+\tau^-$ events with the Belle II experiment

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The Belle-II Collaboration,
Max Planck Institute for Physics, Max Planck Society and Cooperation Partners;

Adachi, I.
Max Planck Institute for Physics, Max Planck Society and Cooperation Partners;

et al.,
Max Planck Institute for Physics, Max Planck Society and Cooperation Partners;

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Citation

The Belle-II Collaboration, Adachi, I., & et al. (2023). Search for a $\tau^+\tau^-$ resonance in $e^{+}e^{-}\rightarrow \mu^{+}\mu^{-} \tau^+\tau^-$ events with the Belle II experiment. Physical Review Letters, 131, 121802. doi:10.1103/PhysRevLett.131.121802.

Cite as: https://hdl.handle.net/21.11116/0000-000F-1298-1

Abstract

We report the first search for a non-standard-model resonance decaying into $\tau$ pairs in $e^{+}e^{-}\rightarrow \mu^{+}\mu^{-} \tau^+\tau^-$ 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 axion-like 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 $\tau$ pairs, ranging from 0.7 fb 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 axion-like particle model over the entire mass range.