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progress14/ChargedParticleAnalysis.tex

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+%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.