The CHY representation of tree-level primitive QCD amplitudes

In this paper we construct a CHY representation for all tree-level primitive QCD amplitudes. The quarks may be massless or massive. We define a generalised cyclic factor (C) over cap (w, z) and a generalised permutation invariant function (E) over cap (z, p, epsilon). The amplitude is then given as a contour integral encircling the solutions of the scattering equations with the product (C) over cap (E) over cap as integrand. Equivalently, it is given as a sum over the inequivalent solutions of the scattering equations, where the summand consists of a Jacobian times the product (C) over cap (E) over cap . This representation separates information: The generalised cyclic factor does not depend on the helicities of the external particles, the generalised permutation invariant function does not depend on the ordering of the external particles.