an upper limit of $N_{\rm qg} = 193$ on the mean for the events with quark–gluon plasma production. In Figure 10 we plot the negatively charged particle multiplicity distribution defined in eq. (\[double\]) for different values of the probability $q$. We use Poisson distributions for $P^{\rm had}$ and $P^{\rm qg}$ and take the upper limit for rare events $N_{\rm qg} = 193$ as the mean for $P^{\rm qg}$. A shoulder develops for small $q$ and becomes more pronounced the larger $q$ is. In Figure 11 we fix $q=0.1$ and investigate the effect of different values of the mean $N_{\rm qg}$ of the distribution for events with some quark–gluon plasma production. If this mean is close to the mean of purely hadronic events we will only find some broadening of the overall distribution. This would be the case if the phase transition is weakly first order or second order. For larger $N_{\rm qg}$ we begin to see a well established shoulder develop. For large $N_{\rm qg}$ a second maximum appears.

It is clear that the exact values of the probability $q$ and of the mean $N_{\rm qg}$ of rare events will be crucial for the experimental observation of a phase transition. 