Speaker
Description
The feasibility of observing true tauonium, the ground bound-state of two tau leptons $\mathcal{T}_0\equiv(\tau^+\tau^-)$, via photon-photon collisions at current and future colliders is studied. The production cross sections of the process $\gamma\gamma\to\mathcal{T}_0\to\gamma\gamma$ ---as well as those of all relevant backgrounds: spin-0 and 2 charmonium resonances decaying to diphotons, and light-by-light scattering--- are computed in the equivalent photon approximation for $e^+e^-$ collisions at BES~III ($\sqrt{s} = 3.8$ GeV), Belle~II ($\sqrt{s} = 10.6$ GeV), and FCC-ee ($\sqrt{s} = 91.2$ GeV), as well as for ultraperipheral p-p, p-Pb, and Pb-Pb collisions at the LHC. Despite very small $\mathcal{T}_0$ production cross sections and a final state swamped by diphoton decays from overlapping pseudoscalar and tensor charmonium states ---the $\chi_{c2}$, $\eta_{c}(2S)$, and $\chi_{c0}$ states have masses only 2.5, 84, and 139 MeV away, respectively, from the $\mathcal{T}_0$ peak--- evidence and observation of the ground state of the heaviest leptonium sytstem appears feasible at Belle-II and FCC-ee, respectively, with in-situ high-precision measurements of the irreducible charmonium backgrounds.
| Submitted on behalf of a Collaboration? | No |
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