Speaker
Description
A calibratable full-event (jet-free) HH→4b framework based on full-event particle-flow (PF) candidates was presented at ML4Jets 2025 and in Refs. 1 and 2, demonstrating a dramatic >5× improvement in search sensitivity over conventional approaches. In this talk, I will present a series of controlled ablation studies that progressively enhance the event representation, providing a detailed understanding of the origin of this dramatic gain in background rejection. I will also introduce an improved training strategy for mass-decorrelated discriminants and a dedicated optimization targeting constraints on the Higgs self-coupling, $\kappa_{\lambda}$.
Starting from a conventional jet-based baseline, in which the kinematic variables and flavour-tagging scores of all small-radius jets are used to train a signal-versus-background event classifier, we progressively enhance the event representation through a sequence of modifications: (a) replacing the handcrafted jet features with 64-dimensional learned jet embeddings extracted from a jet-tagging network (~2× gain in background rejection); (b) jointly training the particle-to-jet encoder (i.e. the jet-tagging network) with the event-level classifier, making the jet representations task-specific (~1.5× gain); (c) removing the per-jet information bottleneck and directly modeling particle-level correlations across jets, yielding the largest individual improvement (~3×); (d) incorporating PF candidates outside reconstructed jets (~1.5–2× gain); and (e) scaling up both the training statistics and model capacity (~2× gain). Altogether, the full-event PF representation achieves ~20× stronger background rejection than the conventional jet-based baseline at representative working points.
Finally, we extend the framework by jointly training on the $\kappa_{\lambda} = 0, 1, 2.45,$ and $5$ hypotheses, allowing the model to learn $\kappa_{\lambda}$-dependent event features and construct a discriminant specifically optimized for constraining the Higgs self-coupling. Preliminary results indicate strong potential for excluding the $\kappa_{\lambda} = 0$ hypothesis.