%Ben and Nam, 1 p, just intro, different analysis active silicon and
%passive Al

%\subsubsection{plan}
%\begin{itemize}
%\item Method:
%\begin{itemize}
%\item Coincidence between thick and thin silicon
%\item Since thin silicon is very thin ( $\sim65~\mu$m ) assume that energy deposited in thin is $E_{\mathrm{thin}}\propto \frac{dE}{dx}$
%\item Then build dE/dx vs E plot from $E_{\mathrm{thin}}$ vs $E_{\mathrm{thick}} + E_{\mathrm{thin}}$
%\item Cuts: muSc coincidence, remove muon pile-up, muSc is muon like, thick and thin coincidence, minimum and maximum energy cuts on thick and thin
%\item Vacuum to prevent scattering of low-energy charged particles
%\end{itemize}
%\item Analysed data-sets:
%\begin{itemize}
%\item  Al100 - Fully unfolded
%\item  Al50 - Folded spectrum, comparison to MC using Al100 unfolded spectrum
%\item  Active SiR2 - Folded but with large background from lack of back wall shielding.  Require additional Active Target coincidence
%\end{itemize}
%\item Backgrounds:
%\begin{itemize}
%\item Pile-up (particularly since only Slow Silicon is used due to calibration data)
%\item Muons stopping in silicon
%\item Random coincidence (particularly in Active Si dataset)
%\end{itemize}
%\end{itemize}


\begin{figure}[htbp]
  \centering
    \includegraphics[width=0.35\textwidth]{figs/SiPackage.jpg}
    \caption{One of the silicon packages used for the charged particle
    measurement. The thin detector is on the near-side to the target, whereas
    the thick detector sits at the back.}
  \label{fig:SiPackage}
\end{figure}

The measurement of charged particles makes use of 4 silicon detectors, two
thick and two thin.  One thick and one thin detector are placed back to back
as shown in Fig.~\ref{fig:SiPackage} so that charged particles pass first
through the thin silicon and stop in the thick (provided their
kinetic energy is not too high, around \SI{18}{MeV}).  
The energy deposited in the thin silicon can be decribed as
\begin{equation}
E_\mathrm{thin} = \frac{dE}{dx} \Delta x
\end{equation}

By comparing this to the total energy deposited by the particle,
$E_\mathrm{total} =  E_\mathrm{thin}+  E_\mathrm{thick}$,
we can build up a typical $\dfrac{dE}{dx}$ curve which allows us to perform
particle identification (PID) based on the two energy measurements.

Since most of the particles being studied are low in energy ($E_k <
\SI{15}{MeV}$) the target and chamber are placed in a vacuum chamber
to reduce scattering and absorption in air. This increases efficiency,
and gives a better estimate of the initial energy.

The analysis of charged particle data uses the muon centred tree approach
described above with the following cuts:
\begin{itemize}
\item {\bf MuSc coincidence.} Hits in the detector should be related to an
incoming muon,
\item {\bf Thick and thin coincidence.} Required for PID,
\item {\bf MuSc is muon like.} Make sure the coincident $\mu$Sc hit was from a muon and
not a beam-electron or otherwise,
\item {\bf Muon pile-up.} Ensures the detected hit is definitely from the right
muon, important when studying the timing of the processes.
\item {\bf Energy cuts on thick and thin.}
\end{itemize}

Of the data taken during R2013, the two aluminium datasets (Al50 and Al100)
have been studied the most. Additionally, data was also taken using one of the
detectors as the target itself which gives additional information as to the
stopping distribution and acceptances.  This silicon dataset (ActiveSi) has only been
partially analysed at this stage.  Table \ref{tab:ChargedParticleDatasets} shows 
a summary of the datasets analysed.

\begin{table}[htbp]
\centering
\caption{Status of the charged particle analysis for different datasets}
\begin{tabular}{p{0.2\textwidth}p{0.7\textwidth}}
\addlinespace
\toprule
\bf Dataset & \bf Analysis status and approach \\ %[0.5ex]
\midrule
Al100 & Fully unfolded \\
\addlinespace
Al50 &  Spectrum at detector, comparison to MC using Al100 unfolded spectrum \\
\addlinespace
Active SiR2 & Spectrum at detector but with large background from lack of back wall shielding.  Requires additional Active Target coincidence \\
\bottomrule
\end{tabular}
\label{tab:ChargedParticleDatasets}
\end{table}

Possible backgrounds to the analysis come from muons scattering into the
detector and stopping in the front face of the thin silicon, random coincidences
between events in the thick and thin detectors, and waveform pile-up caused by 
two or more less energetic particles arriving at the same time.

Muons stopping in the front of the thin silicon are an issue since those that
capture on a silicon nucleus in the detector will emit charged particles which
could---if they pass through the thin and stop in the thick---overlap with the
distribution of the charged particles coming from the target.  Since the
lifetime of silicon is very close to that of aluminium, timing cuts cannot be used to remove this background.  Estimates from Monte Carlo however suggest
there is only  5\% contamination at maximum.
