% CORRETTO BABBO
We were given the possibility to test the behaviour of the prototype with hadron ($\pi^-$) beams. Particle rates went from $1.25kHz$ up to $38kHz$. Unlike muon beams, pion beams were sharp: the particle flux covered an area of approximately $10 \cdot 5 mm^2$.\\
\begin{figure}%[!htbp]
	\centering
	\subfigure[HV scan]
	{\includegraphics[width=6.6cm]{Images/hadrons-hv}\label{pi-full}}
	\hspace{2mm}
	\subfigure[Zoom]
	{\includegraphics[width=6.6cm]{Images/hadrons_zoom}\label{pi-zoom}}
	\caption{High-voltage scan under a beam of pions}
	\label{pai-1}
\end{figure}
\begin{figure}%[!htbp]
	\centering
	\includegraphics[width=12cm]{Images/hadronsmuons-nocolors}%{Images/hadronsmuons}
	\caption{Detector behaviour: comparison between pions exposition and muons exposition}
	\label{pai-2}
\end{figure}

\figurename~\vref{pi-full} shows an HV scan performed for different intensities of the $\pi^-$ beam. However, for some intensity-threshold combinations we only got a few data. The plot shows beam intensities measured in counts per spill; each spill lasted $10s$. \figurename~\ref{pai-2} represents a comparison between pion beam and muon beam HV scans. It only shows data collected at threshold $-60ds$, so to compare two scans with the same settings.\\

We may infer from \figurename~\ref{pai-2} that the prototype presents higher efficiency when detecting hadrons. However, due to the large rate difference between muon beam ($0.8kHz$) and hadron beam (\figurename~\ref{pai-2} plots the set of data collected when the beam intensity was $38kHz$), we can not state clearly whether the increase in efficiency is caused by the presence of hadrons. An effect of \textbf{charging up} may have indeed occured in this case: as a result of the higher interaction rate inside the detector, some of the electrons produced in the avalanche may have accumulated on the insulator surface by the GEM holes (which are not perfectly straight). As a consequnce, the electric field inside the holes would have been strenghtened, raising the GEM foil gain with no need of increasing the external voltage. The visible effect of this kind of \textit{charging up} should be a raise of efficiency at constant divider current, as we may recognize in \figurename~\vref{pai-2}. \figurename~\vref{pi-zoom} focusses on the slightly different behaviours of the detector when working at different rates. To verify this, we shall perform further laboratory tests, with different intensities X-Rays, or maybe organize future test-beam sessions aimed at solving this question.