Prospects for ditauonium discovery at colliders

TL;DR

This paper evaluates the potential for discovering ditauonium, a tau lepton bound state, at various colliders, proposing specific production channels and estimating yields and detection strategies across different experimental setups.

Contribution

It provides the first detailed analysis of ditauonium production and detection prospects at multiple colliders, including novel methods for tau mass measurement and decay observation.

Findings

Para-ditauonium observable at FCC-ee via photon fusion

Ortho-ditauonium detectable at STCF through muon decay channels

Potential to measure tau mass with ~25 keV precision at threshold scans

Abstract

The feasibility of observing ditauonium, the bound state of two tau leptons, at $e^+e^-$ colliders (BES III at $\sqrt{s} = 3.78$ GeV, Belle II at $\sqrt{s} = 10.6$ GeV, a future super tau-charm factory (STCF) at $\sqrt{s} \approx 2m_{\tau}$, and the FCC-ee at $\sqrt{s} = 91.2$ GeV) as well as in hadronic and photon-photon collisions at the LHC, is studied. Cross sections and expected yields for spin-0 para- ($\mathcal{T}_0$) and spin-1 ortho- ($\mathcal{T}_1$) ditauonium are presented for nine different production and decay processes. Para-ditauonium can be observed at the FCC-ee via photon fusion in its diphoton decay ($\gamma\gamma\to\mathcal{T}_0\to\gamma\gamma$). Ortho-ditauonium can be observed at STCF via $e^+e^-\to\mathcal{T}_1\to\mu^+\mu^-$, where a threshold scan with monochromatized beams can also provide a very precise extraction of the tau lepton mass with a $\mathcal{O}(25$ keV) uncertainty or less. Observing pp $\to \mathcal{T}_1(\mu^+\mu^-)+X$ at the LHC is possible by identifying its displaced vertex with a good control of the combinatorial dimuon background. In addition, we compute the rare decay branching fractions of ditauonium into quarkonium plus a photon.