% CORRETTO BABBO
\begin{figure}[tbp]	% b/n
	\centering
	\subfigure[Beam on \textit{zone A} pads]
	{\includegraphics[width=12cm]{Images/HVscanA-nocolors}\label{hva}}
	\subfigure[Beam on \textit{zone P} pads]
	{\includegraphics[width=12cm]{Images/HVscanP-nocolors}\label{hvp}}
	\caption{High voltage scans performed with beam on zones \textit{A} and \textit{P}}
	\label{hvap}
\end{figure}
%\begin{figure}[tbp]
%	\centering
%	\subfigure[Beam on \textit{zone A} pads]
%	{\includegraphics[width=12cm]{Images/HVscanA}\label{hva}}
%	\subfigure[Beam on \textit{zone P} pads]
%	{\includegraphics[width=12cm]{Images/HVscanP}\label{hvp}}
%	\caption{High voltage scans performed with beam on zones \textit{A} and \textit{P}}
%	\label{hvap}
%\end{figure}

Efficiency was first detected as a function of the High-Voltage (subsequently referred to as \textbf{HV}) applied on the divider poles. These scans were performed focusing 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), obtaining slightly different results. This was done to check the LG homogeneity, since it is a large area detector.\\

The gas mixture inside the detector was Ar/CO\subscript{2} in 70/30 proportions.\\

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}) to detect the signal as well as possible; in \textit{point A} we also repeated the scan setting $MSPL=3clk$.\\

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

Major efficiency at lower HV values is noticeable on the region made of smaller pads. This effect may be due to the capacitance of the pads themselves, which affects the signal where the pads are large. A study was done about this and will be presented later in this thesis.\\

In zone \textit{A} we reached an efficiency of about $95\%$ or higher, at thresholds $-40ds$ and $-60ds$, already with a divider current $I_D=817 \mu A$, and at $I_D=850 \mu A$ we got $\varepsilon \simeq 98 \%$ for all the four threshold values. $MSPL=3clk$ graphs do not diverge appreciably from the $MSPL=4clk$ ones.\\
Instead, in zone \textit{P} the LG prototype approached the 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 made an HV scan after changing the detector gas mixture, as described in \chaptername~\vref{subsec-timing}. We added CF\subscript{4} inside the detector, resulting in a lowering of the 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 work with  CF\subscript{4}, changing the internal electric fields of the detector.