Search for low-mass resonances decaying to $ττ$ and measurement of the $Υ$$→$$ττ$ decay in proton-proton collisions at √s = 13.6 TeV

An inclusive search is presented for spin-zero bosons decaying to $ττ$ in a previously unexplored mass range between 20 and 60 GeV using proton-proton collision data at √s = 13.6 TeV, corresponding to an integrated luminosity of 61.9 fb⁻¹ recorded by CMS in 2022$-$2023. A high-rate trigger stream in combination with a novel low-momentum hadronic tau reconstruction algorithm have enabled a measurement of the $Υ$(1S,2S,3S) →τ^+τ^-$ process in the challenging environment of a hadron collider, with a 5.8$σ$ significance above background and production cross section of 3.5 $±$ 0.7 (stat) $±$ 0.7 (syst) nb for visible rapidity $ yᵥᵢₛ< 1.2 and visible transverse momentum pTᵛis>$ 15 GeV. No significant excess above the standard model background is observed. Upper limits on the product of the spin-zero resonance production cross section and branching fraction to $ττ$ are set at 95% confidence level between 40 and 400 pb.