Enhancing the t t ¯ H tt̄ H signal through top-quark spin polarization effects at the LHC

We compare the impact of top-quark spin polarization effects in Higgs boson production in association with top-quark pairs and in corresponding backgrounds at the LHC. Because of the spin-zero nature of the Higgs boson, one expects, in the chiral limit for the top quarks, a substantial complementarity in tt̄ spin correlations for a Higgs decaying into fermions/gauge-bosons and tt̄ spin correlations for the corresponding irreducible tt̄ ff̄ /VV backgrounds. Although top mass effects in tt̄ H production are in general dominant, and seriously spoil the chiral-limit expectations, one can find observables that capture the tt̄ angular spin correlations and can help in separating the signal from irreducible backgrounds. In particular, we show that, for both H → bb̄ and H → γγ, taking into account tt̄ spin correlations in tt̄ H production and irreducible backgrounds could appreciably improve the LHC sensitivity to the tt̄ H channel.