Machine learning the Higgs boson-top quark CP phase

Abstract

We explore the direct Higgs boson-top CP measurement via the pp→tt¯h channel at the high-luminosity LHC. We show that a combination of machine learning techniques and efficient kinematic reconstruction methods can boost new physics sensitivity, effectively probing the complex tt¯h multiparticle phase space. Special attention is devoted to top quark polarization observables, uplifting the analysis from a raw rate to a polarization study. Through a combination of hadronic, semileptonic, and dileptonic top pair final states in association with h→γγ, we obtain that the HL-LHC can probe the Higgs boson-top coupling modifier and CP phase, respectively, up to |κt| 8% and |α| 13° at 68% C.L.