Speaker
Description
Electron-positron collisions provide a uniquely clean environment for precision studies of jets and Quantum Chromodynamics, free from hadronic initial-state effects and with a well-defined hard-process energy scale. Recent progress in archival-data preservation and modern analysis techniques has opened a new program of jet and energy-flow measurements using LEP data, allowing contemporary jet-substructure tools to be applied to high-resolution $e^+e^-$ events. In this talk, we present recent results from the Electron-Positron Alliance based on archived ALEPH and DELPHI data. The measurements include anti-$k_T$ jet spectra across different resolution parameters, substructure observables, energy-energy correlators, and thrust in hadronic $Z$ decays and related measurements. These observables probe perturbative radiation, hadronization, and the transition from partons to hadrons in a single clean experimental setting. The results are compared with modern event generators and, where available, perturbative and resummed QCD calculations. Together, these measurements establish LEP archival data as a precision laboratory for modern jet physics. They provide stringent constraints on event-generator modeling, new baselines for jet-substructure measurements at hadron colliders, and important inputs for future $e^+e^-$ collider programs. They also demonstrate the broader potential of the "recycling frontier": extracting new QCD information from preserved collider datasets using modern theoretical and experimental tools.