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 s=3.78 GeV, Belle II at s=10.6 GeV, a future super tau-charm factory (STCF) at s≈2mτ, and the FCC-ee at 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- (T0) and spin-1 ortho- (T1) 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 (γγ→T0→γγ). Ortho-ditauonium can be observed at STCF via e+e−→T1→μ+μ−, where a threshold scan with monochromatized beams can also provide a very precise extraction of the tau lepton mass with O(25 keV) uncertainty. Observing pp →T1(μ+μ−)+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.