Speaker
Description
The Higgs sector represents one of the least well-measured areas of high-energy particle physics. A key interest lies in the measurement of the Higgs self-coupling $\lambda_{HHH}$, which would establish the mechanism of electroweak symmetry breaking. This contribution follows last year's input to the European Strategy for Particle Physics Update (ESPPU), which extrapolated the sensitivity to $\lambda_{HHH}$ via $\mathrm{e}^+\mathrm{e}^- \to \mathrm{ZHH}$ at a Linear Collider Facility (LCF) operating at the elevated $\sqrt{s} = 550$ GeV with the International Large Detector (ILD), together with a full re-analysis of the $\mathrm{Z} \to \mathrm{e}^+\mathrm{e}^-/\mathrm{\mu}^+\mathrm{\mu}^-$ channels. Here we present our latest improvements: the inclusion of the $\mathrm{Z} \to \mathrm{\nu}\bar{\mathrm{\nu}}$ channel, a first look at the $\mathrm{Z} \to \mathrm{q}\bar{\mathrm{q}}$ and $\mathrm{Z} \to \mathrm{\tau}^+ \mathrm{\tau}^-$ channels, a more elaborate extraction of $\lambda_{HHH}$ and an explicit study of beyond-the-Standard-Model (BSM) cases. These analyses take into account an extensive range of Standard Model backgrounds and employ dedicated algorithms for event reconstruction and analysis; in particular, we make use of hard-scattering matrix elements for background rejection and machine learning for jet flavor tagging, overlay rejection and multi-class event classification.