AI and the World's Hard Problems · Physics · arXiv · 2026-10-21
Pretraining on boosted boson decays for polarization tagging of hadronic $W$ bosons
At large boosts, longitudinal and transverse W bosons produce jets with the same mass and two-prong structure, distinguishable only by the decay angle, and longitudinal bosons occur in just 0.3% of W+jet events. Because polarized samples are costly to simulate, the authors pretrain a point-edge transformer on 10⁷ unpolarized jets and fine-tune it on few labels to see how much polarization information a tagger can recover. Pretraining beats training from scratch, though generic pretraining on a broad jet mix and a boosted decision tree do as well; the production angle reconstructed from the recoiling jet improves every tagger, and moving from a jet tagger to an event-level tagger brings significant gains.