Speaker
Description
Searches for the production of $\tau$-sleptons ($\tilde{\tau}$), charginos ($\tilde{\chi}_1^\pm$), and neutralinos ($\tilde{\chi}_2^0$) in events with at least one hadronically decaying $\tau$-lepton are presented, targeting compressed mass spectra scenarios. To enhance sensitivity to compressed mass spectra, production modes with initial-state radiation (ISR) jets are considered. The searches use $140\,\mathrm{fb}^{-1}$ and $53\,\mathrm{fb}^{-1}$ of proton--proton collision data recorded by the ATLAS detector at the Large Hadron Collider during 2015--2018 at a centre-of-mass energy of $\sqrt{s} = 13\,\mathrm{TeV}$ and during 2022--2023 at $\sqrt{s} = 13.6\,\mathrm{TeV}$, respectively. The searches provide expected sensitivity to compressed mass spectra scenarios with light $\tau$-sleptons. The results are generally consistent with the Standard Model, with several deviations having local significances of $2.1$--$2.4\sigma$. These deviations weaken the observed exclusion limits. For direct $\tau$-slepton production, in the ISR channel alone, exclusion limits are set for $\Delta m(\tilde{\tau}, \tilde{\chi}_1^0) = 30\,\mathrm{GeV}$ for $\tau$-slepton masses up to $115\,\mathrm{GeV}$ at 95\% confidence level. Given the observed deviations, no exclusion limits are set for direct $\tau$-slepton production when statistically combining all considered channels. For electroweakino production, exclusion limits are set for $\Delta m(\tilde{\chi}_2^0, \tilde{\chi}_1^0) = 30\,\mathrm{GeV}$ for $\tilde{\chi}_2^0$ masses up to $200\,\mathrm{GeV}$. For pure chargino pair production, exclusion limits are set for chargino masses up to $175\,\mathrm{GeV}$ for the same mass splitting.
