Prospects for ditauonium discovery at colliders

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.

Comments: 15 pages, 6 figures. Minor mods. to match published version: Phys. Lett. B 842 (2023) 137960