Search for low-mass resonances decaying to $\tau\tau$ and measurement of the $\Upsilon$ $\to$ $\tau\tau$ decay in proton-proton collisions at $\sqrt{s}$ = 13.6 TeV

An inclusive search is presented for spin-zero bosons decaying to $\tau\tau$ in a previously unexplored mass range between 20 and 60 GeV using proton-proton collision data at $\sqrt{s}$ = 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 $\Upsilon$(1S,2S,3S) $\to$ $\tau^+\tau^-$ process in the challenging environment of a hadron collider, with a 5.8$\sigma$ significance above background and production cross section of 3.5 $\pm$ 0.7 (stat) $\pm$ 0.7 (syst) nb for visible rapidity $\lvert y_{\text{vis}}\rvert$ $\lt$ 1.2 and visible transverse momentum $p_\mathrm{T}^\text{vis}$ $\gt$ 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 $\tau\tau$ are set at 95% confidence level between 40 and 400 pb.