Higgs Self-Coupling Measurement with the XCC (XFEL Compton Collider) Concept

This study presents the first physics simulation of the XCC, an X-ray Free-Electron-Laser-based γγ Compton collider, focusing on the key case of measuring the Higgs self-coupling — a parameter fundamental to understanding the Higgs sector in the SM and exploring new physics. The XCC is emerging as a promising candidate for the HEP community's goal of developing a Higgs factory. This linear γγ collider concept uses 62.6 GeV (190 GeV) electron beams and 1 keV X-ray laser beams to produce high-energy photon collisions for single (double) Higgs production at 125 GeV (380 GeV) center-of-mass energy. In contrast to earlier γγ collider concepts from the 1990’s, and leveraging the significant advancements of X-ray-Free-Electron-Lasers (XFELs) over the last decades, XCC uses x-ray rather than optical photons. This innovation results in a sharply peaked γγ center-of-mass energy spectrum that enables precise measurements of the di-Higgs cross-section at 380 GeV and enhances the sensitivity and signal significance. Using a Delphes ILC-like detector model, this work shows a feasibility study for measuring the Higgs self-coupling with XCC. All physics backgrounds as well as the residual eγ background characteristic of γγ colliders are included. The results, including the uncertainty and statistical significance of the cross-section measurement, are pivotal in demonstrating the XCC's potential to deliver high-precision Higgs self-coupling measurements.