Search for a dark leptophilic scalar produced in association with ${\tau }^{+}{\tau }^{-}$ pair in $e^{+}{e}^{-}$ annihilation at center-of-mass energies near 10.58 GeV

Abstract

A dark leptophilic scalar $({\varphi }_L)$ is a hypothetical particle that couples only to leptons rather than quarks. We report on a search for ${\varphi }_L$ in the $e^{+}{e}^{-}\to {\tau }^{+}{\tau }^{-}{\varphi }_L,{\varphi }_L\to {\ell }^{+}{\ell }^{-}(\ell =e,\mu )$ process using 626~\invfb of data collected by the Belle experiment near the \Y4S resonance. We validate the backgrounds with multiple control regions in data, using a novel multiclass multivariate event classifier. In absence of a signal, we quote upper limits at the 90\% confidence level on the coupling between ${\varphi }_L$ and leptons. Our bounds, obtained in a blinded approach, are 19\% more constraining than the previous limits, averaged over the mass range $0.04 \leq m_{ϕ_L} \leq 6.5~\gev$. We exclude the parameter space below 4~\gev favored by measurement of the anomalous magnetic moment of the muon.

arXiv comment8 pages, 7 figures

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