Production of leptonium in heavy quarkonium decays

TL;DR

This paper explores the production of leptonium bound states in heavy quarkonium decays, highlighting the potential for observing various leptonium species at future high-luminosity facilities like STCF.

Contribution

It provides theoretical predictions for leptonium production rates in heavy quarkonium decays, emphasizing the feasibility of detecting these states at upcoming experiments.

Findings

Potential observation of positronium, muonium, and dimuonium at STCF.

Predicted branching fraction for ortho-dimuonium production in J/ψ decays.

Estimated number of events for leptonium detection at future colliders.

Abstract

Lepton pairs with opposite charges can form bound states known as ``leptonium'' through quantum electrodynamic interactions. Heavy quarkonia such as $J/\psi$ are abundantly produced at facilities like BESIII and the future Super Tau-Charm Facility (STCF). In this work, we investigate leptonium production in heavy quarkonium decays, specifically focusing on the processes ${\cal{Q}} \longrightarrow (l_1^+ l_2^-)[n] +\gamma$ ($l_{1,2}= \tau,\, \mu,\, e$) and ${\cal{Q}} \longrightarrow (l_1^+ l_2^-)[n] + l_1^- l_2^+$. Here, ${\cal{Q}}$ denotes the heavy quarkonium $J/\psi$ or $\Upsilon$, while $n=$ ${^1S_0}$ or $^3S_1$ corresponds to para-leptonium and ortho-leptonium, respectively. With an annual production of $3.4 \times 10^{12}$ $J/\psi$ events at STCF, there is significant potential to observe positronium $(e^+e^-)$, muonium $(\mu^+e^-)$, and dimuonium $(\mu^+\mu^-)$. In particular, the ortho-dimuonium $(\mu^+\mu^-)[^3S_1]$ may be discovered at the future STCF, with an inclusive branching fraction of $Br(J/\psi \longrightarrow (\mu^+\mu^-)[^3S_1] +X) = 1.5 \times 10^{-12}$.