Let $M$ be a compact Riemannian manifold without boundary. Distinct $k$-points $x_1,\cdots,x_k\in M$ are called stable if the potential energy given by coulomb forces among $k$ electrons reaches minimal locally at $(x_1,\cdots,x_k)$. The $k$-th stable configuration space is defined by $$ S(M,k)=\{(x_1,\cdots,x_k)\in M^k\mid x_1,\cdots,x_k \text{ are distinct and stable}. \} $$
Let the $k$-th permutation group $\Sigma_k$ act on $S(M,k)$ by permuting coordinates. The $k$-th stable braid space is defined by $$ S(M,k)/\Sigma_k. $$
Question: Given $k\geq 2$ and $M$, what is the cohomology ring $H^*(S(M,k)/\Sigma_k)$? Some nontrivial examples & references are also wanted.