  The Haldane-Shastry spin chain can be mapped to the infinite coupling limit
of the SU(2) spin Calogero-Sutherland model. We use the $\mathfrak{gl}_2$ Jack
polynomials' technology to compute the form factors of the spin operator on the
multi-spinon spectrum. The spin structure factor is obtained through a form
factor expansion. The expansion is proven to converge in the small momentum
limit. Numerics based on two- and four-spinons contributions give an
approximate result for the infinite temperature static and dynamic spin
structure factor.
