Dr. James Frost

Abstract:

The plasmon excitations of the degenerate free-electron gas in the surface space-charge region of InSb have been studied using high-resolution electron-energy-loss spectroscopy. Semiclassical dielectric theory simulations of the energy-loss spectra have been performed using the hydrodynamic and Boltzmann-Mermin models. While both analyses include the effects of temperature, conduction band nonparabolicity, spatial dispersion and collisional damping, the hydrodynamic model is not able to quantitatively reproduce the experimental spectra at higher excitation wave vectors. The measured spectral shapes are only accurately reproduced when collisionless plasmon damping is included explicitly using the Boltzmann-Mermin dielectric function. © 2006 The American Physical Society.

Abstract:

Measuring the Higgs trilinear self-coupling $\lambda_{hhh}$ is experimentally demanding but fundamental for understanding the shape of the Higgs potential. We present a comprehensive analysis strategy for the HL-LHC using di-Higgs events in the four $b$-quark channel ($hh \to 4b$), extending current methods in several directions. We perform deep learning to suppress the formidable multijet background with dedicated optimisation for BSM $\lambda_{hhh}$ scenarios. We compare the $\lambda_{hhh}$ constraining power of events using different multiplicities of large radius jets with a two-prong structure that reconstruct boosted $h \to bb$ decays. We show that current uncertainties in the SM top Yukawa coupling $y_t$ can modify $\lambda_{hhh}$ constraints by $\sim 20\%$. For SM $y_t$, we find prospects of $-0.8 < \lambda_{hhh} / \lambda_{hhh}^\text{SM} < 6.6$ at 68% CL under simplified assumptions for 3000~fb$^{-1}$ of HL-LHC data. Our results provide a careful assessment of di-Higgs identification and machine learning techniques for all-hadronic measurements of the Higgs self-coupling and sharpens the requirements for future improvement.