On the mean free paths of pions and kaons in hot hadronic matter
  Pion and kaon mean free paths within a thermal hadronic background are calculated using relativistic kinetic theory. Free cross sections are used which include contributions from $\rho$, $K^{*}$, $\Delta$ and heavier resonances. Given pion to baryon ratios appropriate for the breakup stage of a $200\cdot A$GeV relativistic-heavy-ion collision, we find for temperatures less than 100 MeV, kaons have a shorter mean free path than pions, while for higher breakup temperatures the reverse is true. Since breakup temperatures should be in the neighborhood of 100 MeV, this suggests that kaon interferometry samples the same emission distribution as pion interferometry. 
Kevin Haglin and Scott Pratt