Marstrand's density theorem in the Heisenberg group

We prove that if $\mu$ is a Radon measure on the Heisenberg group $\mathbb{H}^n$ such that the density $\Theta^s(\mu,\cdot)$, computed with respect to the Kor\'anyi metric $d_H$, exists and is positive and finite on a set of positive $\mu$ measure, then $s$ is an integer. The proof relies on an analysis of uniformly distributed measures on $(\mathbb{H}^n,d_H)$. We provide a number of examples of such measures, illustrating both the similarities and the striking differences of this sub-Riemannian setting from its Euclidean counterpart.