Probing the Higgs Self-Coupling with an XFEL Compton $\gamma\gamma$ Collider at $\sqrt{s} = 380$ GeV

Abstract

We present a study probing the Higgs self-coupling with the X-ray free-electron laser Compton $\gamma\gamma$ Collider (XCC) concept. The analysis is performed considering the $\gamma\gamma \to HH \to bb\overline{bb}$ channel, and results are then extrapolated to obtain a projection on the Higgs self-coupling sensitivity that ranges between 7% and 12%. An ensemble of boosted decision trees is trained to discriminate between signal and backgrounds, paired with a genetic algorithm optimizer to combine the final classifier outputs. This study suggests that an X-ray FEL-based $\gamma\gamma$ collider is a powerful tool to probe the mechanism of electroweak symmetry breaking, complementary to $e^+e^-$ Higgs factories and future high-energy hadron colliders.