Speakers
Description
Precise, high-energy $e^{+}e^{-}$ data remain essential for a global understanding of particle physics. Despite decades since the end of the Large Electron-Positron Collider (LEP), such data continue to play a central role in precision measurements and the tuning of phenomenological models in parton shower Monte Carlo (MC) simulations. One particularly important observable is thrust, which probes QCD dynamics by measuring the alignment of hadronic final states into dijet-like topologies. Thrust has been widely used to extract the strong coupling constant $\alpha_{s}(m_{Z})$, tune hadronization models, and study non-perturbative effects. Recent theoretical developments have renewed the focus on thrust, revealing discrepancies between precision extractions of $\alpha_{s}(m_{Z})$ from dijet observables and the world average, and emphasizing the relevance of thrust moments in constraining both perturbative and non-perturbative QCD components. The fixed binning choices in existing LEP thrust measurements, however, has emerged as a key limitation that restricts the scope of studies utilizing the results. In this work, we present the first unbinned measurement of the $\log(1 - T)$ distribution in $e^{+}e^{-}$ collisions at $\sqrt{s} = 91.2$ GeV using archived data from the ALEPH experiment at LEP. The thrust is reconstructed from charged and neutral particles in hadronic $Z$ decays. Detector effects are corrected using an ML-based method for unbinned unfolding called UniFold, allowing downstream fully differential and variable binning studies. This measurement provides valuable input for ongoing theoretical developments, MC tuning, and opens the door to new studies of $e^{+}e^{-}$ data.
