  We consider fermions on a honeycomb lattice supplemented by a spin invariant
interaction that dynamically generates a quantum spin Hall insulator. This
lattice model provides an instance of Gross-Neveu Heisenberg criticality, as
realized for example by the Hubbard model on the honeycomb lattice. Using
auxiliary field quantum Monte Carlo simulations we show that we can compute
with unprecedented precision susceptibilities of the order parameter. In O(N)
Gross-Neveu transitions, the anomalous dimension of the bosonic mode grows as a
function of N such that in the large-N limit it is of particular importance to
consider susceptibilities rather than equal time correlations so as to minimize
contributions from the background. For the N=3 case, we obtain $1/\nu=1.11(4)$,
$\eta_{\phi}=0.80(9)$, and $\eta_{\psi}=0.29(2)$ for respectively the
correlation length exponent, bosonic and fermionic anomalous dimensions.
