  The excitation spectrum of specific conformal field theories (CFT) with
central charge $c=1$ can be described in terms of quasi-particles with charges
$Q=-p,+1$ and fractional statistics properties. Using the language of Jack
polynomials, we compute form factors of the charge density operator in these
CFTs. We study a form factor expansion for the finite temperature
density-density correlation function, and find that it shows a quick
convergence to the exact result. The low-temperature behavior is recovered from
a form factor with $p+1$ particles, while the high-temperature limit is
recovered from states containing no more than 3 particles.
