Top-quark initiated processes at high-energy hadron colliders

In hadronic collisions at high energies, the top-quark may be treated as a parton inside a hadron. Top-quark initiated processes become increasingly important since the top-quark luminosity can reach a few percent of the bottom-quark luminosity. In the production of a heavy particle H with mass m(H) > m(t), treating the top-quark as a parton allows us to resum large logarithms log(m(H)(2)/m(t)(2)) arising from collinear splitting in the initial state. We quantify the effect of collinear resummation at the 14-TeV LHC and a future 100-TeV hadron collider, focusing on the top-quark open-flavor process gg -> t (t) over barH in comparison with t (t) over bar -> H and tg -> tH at the leading order (LO) in QCD. We employ top-quark parton distribution functions with appropriate collinear subtraction and power counting. We find that (1) collinear resummation enhances the inclusive production of a heavy particle with m(H) approximate to 5 TeV (0.5 TeV) by more than a factor of two compared to the open-flavor process at a 100-TeV (14-TeV) collider; (2) top-quark mass effects are important for scales m(H) near the top-quark threshold, where the cross section is largest. We advocate a modification of the ACOT factorization scheme, dubbed m-ACOT, that consistently treats heavy-quark masses in hadronic collisions with two initial heavy quarks; (3) the scale uncertainty of the total cross section in m-ACOT is of about 20% at the LO. While a higher-order calculation is indispensable for a precise prediction, the LO cross section is well described by the process t (t) over bar -> H using an effective factorization scale significantly lower than m(H). We illustrate our results by the example of a heavy spin-0 particle. Our main results also apply to the production of particles with spin-1 and 2.