Fig. 3.

$\gamma$ Peak produced by the decay of ${}^{65}$Zn. Top: events in which the acquisition window contains a single pulse. Bottom: events in which the acquisition window contains more than one pulse. The spectra are fitted simultaneously with an unbinned extended maximum likelihood fit (RooFit analysis framework) with two components: the function modeling the detector response $\Sigma (\mu ,\sigma (E))$, and an exponential background