Enhancing the t(t)over-tildeH 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 t (t) over bar spin correlations for a Higgs decaying into fermions/gauge-bosons and t (t) over bar spin correlations for the corresponding irreducible t (t) over bar f (f) over bar /VV backgrounds. Although top mass effects in t (t) over barH production are in general dominant, and seriously spoil the chiral-limit expectations, one can find observables that capture the t (t) over bar angular spin correlations and can help in separating the signal from irreducible backgrounds. In particular, we show that, for both H -> b (b) over bar and H -> gamma gamma, taking into account t (t) over bar spin correlations in t (t) over barH production and irreducible backgrounds could appreciably improve the LHC sensitivity to the t (t) over barH channel.