% CORRETTO BABBO
\begin{figure}[tbp]
	\centering
	\subfigure[\textit{Zone A}: beam on small pads]
	{\includegraphics[width=12cm]{Images/HVscanA-nocolors}\label{hva}}
	\subfigure[\textit{Zone P}: beam on large pads ($MSPL=4clk$)]
	{\includegraphics[width=12cm]{Images/HVscanP-nocolors}\label{hvp}}
	\caption{High voltage scans performed with a muon beam focussed on zones \textit{A} and \textit{P}}
	\label{hvap}
\end{figure}

The prototype efficiency was first computed as a function of the High-Voltage (subsequently referred to as \textbf{HV}) applied to the divider poles. These scans were performed focussing the muon beam on two regions of the chamber (\textit{P} and \textit{A}, whose readout plane areas are covered respectively with large and small pads). We did it in order to check the behaviour of our detector with VFAT2 front-ends in the two extreme pad sizes. Slightly different results were obtained.\\

Four different thresholds were applied, in order to have a complete set of data to be used as reference for future comparison: $-40$ \textit{DAC steps} (subsequently called \textit{ds}), $-60ds$, $-80ds$ and $-100ds$.
The lenght of the monostable pulse (subsequently referred to as \textbf{MSPL}) was set at 4 \textit{clock cycles} (\textit{clk}); in \textit{point A} we also repeated the scan with $MSPL=3clk$.\\

\figurename~\vref{hva} shows the results of the HV scan performed when the beam was centered on \textit{A}, while \figurename~\ref{hvp} shows the results for \textit{P}.\\

The two figures show a higher efficiency at lower HV values on the region made of smaller pads. At first we supposed that this effect might be due to the capacitance of the pads themselves, which affects the signal where the pads are large. We studied this phenomenon, but the results (presented in \chaptername~\vref{ch-pad_d}) demonstrated that there should be another reason for this efficiency gap.\\

In zone \textit{A} we reached about $95\%$ or higher efficiency ($\varepsilon$) at thresholds $-40ds$ and $-60ds$, already with a divider current $I_D=817 \mu A$. At $I_D=850 \mu A$ we got $\varepsilon \simeq 98 \%$ for all the four threshold values. $MSPL=3clk$ graphs do not diverge significantly from $MSPL=4clk$ ones. Instead, in zone \textit{P} the LG prototype approached full efficiency for all thresholds only at $I_D \geq 866 \mu A$, with $\varepsilon > 95 \%$ at $I_D=850 \mu A$ only for $th=-40ds$ and $th=-60ds$ data sets.\\

\begin{figure}[tbp]
	\centering
	\includegraphics[width=12cm]{Images/gasComp-nocolors}%{Images/gasComp} %colors
	\caption{High voltage scan performed using an Ar/CO\subscript{2}/CF\subscript{4} $60/20/20$ gas mixture (same internal voltages and fields as for Ar/CO\subscript{2})}
	\label{hvcf4}
\end{figure}
We also ran an HV scan after changing the gas mixture inside the detector, as described in \chaptername~\vref{subsec-timing}. We added tetrafluoromethane (CF\subscript{4}), obtaining a lower gain. \figurename~\vref{hvcf4} shows a comparison of the prototype efficiency with its standard gas mixture (Ar/CO\subscript{2} $70/30$) and with CF\subscript{4} (Ar/CO\subscript{2}/CF\subscript{4} $60/20/20$). I will come back on the purpose of this scan in \chaptername~\vref{subsec-timing}. The loss of efficiency at lower current levels may be reduced by optimizing the divider in order to make the detector work with CF\subscript{4} with appropriate internal electric fields.