The Shape of the Correlation Function

The correlation function measured in ultrarelativistic nuclear collisions is strongly non-Gaussian. Using two different models we study which effects can influence its shape and how much. In particular, we focus on the parametrizations expressed with the help of L'evy-stable distributions. We show that the L'evy index may deviate substantially from 2 due to non-critical effects such as resonance decays, event-by-event fluctuations and functional dependence on $Q_{LI}$ or similar. We also study the corrections including the first-order L'evy expansion.