Hits to Higgs: Reconstruction-Free Higgs Classification from Raw LHC Detector Data Using Higgsformers

Abstract: We present a comparative study of Higgs event classification at the Large Hadron Collider that bypasses the traditional reconstruction chain. As a benchmark, we focus on distinguishing ( t\bar{t}H ) from ( t\bar{t} ) events with ( H \to b\bar{b} ), a particularly challenging task due to their similar final-state topologies. Our pipeline begins with event generation in \texttt{Pythia8}, fast simulation with ACTS/Fatras, and classification directly from raw detector hits. We show for the first time that a transformer model originally developed for inner tracker hit-to-track assignment can be retrained to classify Higgs events directly from raw hits. For comparison, we reconstruct the same events with \texttt{Delphes} and train object-based classifiers, including multilayer perceptrons and the Particle Transformer. We evaluate both approaches under varying dataset sizes and pileup levels. Despite operating solely on inner tracker hits, Higgsformer achieves strong performance, reaching an AUC of 0.792.