107 lines
4.9 KiB
TeX
107 lines
4.9 KiB
TeX
%Ben and Nam, 1 p, just intro, different analysis active silicon and
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%passive Al
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%\subsubsection{plan}
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%\begin{itemize}
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%\item Method:
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%\begin{itemize}
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%\item Coincidence between thick and thin silicon
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%\item Since thin silicon is very thin ( $\sim65~\mu$m ) assume that energy deposited in thin is $E_{\mathrm{thin}}\propto \frac{dE}{dx}$
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%\item Then build dE/dx vs E plot from $E_{\mathrm{thin}}$ vs $E_{\mathrm{thick}} + E_{\mathrm{thin}}$
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%\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
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%\item Vacuum to prevent scattering of low-energy charged particles
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%\end{itemize}
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%\item Analysed data-sets:
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%\begin{itemize}
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%\item Al100 - Fully unfolded
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%\item Al50 - Folded spectrum, comparison to MC using Al100 unfolded spectrum
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%\item Active SiR2 - Folded but with large background from lack of back wall shielding. Require additional Active Target coincidence
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%\end{itemize}
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%\item Backgrounds:
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%\begin{itemize}
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%\item Pile-up (particularly since only Slow Silicon is used due to calibration data)
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%\item Muons stopping in silicon
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%\item Random coincidence (particularly in Active Si dataset)
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%\end{itemize}
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%\end{itemize}
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\begin{figure}[htbp]
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\centering
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\includegraphics[width=0.35\textwidth]{figs/SiPackage.jpg}
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\caption{One of the silicon packages used for the charged particle
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measurement. The thin detector is on the near-side to the target, whereas
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the thick detector sits at the back.}
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\label{fig:SiPackage}
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\end{figure}
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The measurement of charged particles makes use of 4 silicon detectors, two
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thick and two thin. One thick and one thin detector are placed back to back
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as shown in Fig.~\ref{fig:SiPackage} so that charged particles pass first
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through the thin silicon and stop in the thick (provided their
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kinetic energy is not too high, around \SI{18}{MeV}).
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The energy deposited in the thin silicon can be decribed as
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\begin{equation}
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E_\mathrm{thin} = \frac{dE}{dx} \Delta x
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\end{equation}
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By comparing this to the total energy deposited by the particle,
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$E_\mathrm{total} = E_\mathrm{thin}+ E_\mathrm{thick}$,
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we can build up a typical $\dfrac{dE}{dx}$ curve which allows us to perform
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particle identification (PID) based on the two energy measurements.
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Since most of the particles being studied are low in energy ($E_k <
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\SI{15}{MeV}$) the target and chamber are placed in a vacuum chamber
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to reduce scattering and absorption in air. This increases efficiency,
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and gives a better estimate of the initial energy.
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The analysis of charged particle data uses the muon centred tree approach
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described above with the following cuts:
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\begin{itemize}
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\item {\bf MuSc coincidence.} Hits in the detector should be related to an
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incoming muon,
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\item {\bf Thick and thin coincidence.} Required for PID,
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\item {\bf MuSc is muon like.} Make sure the coincident $\mu$Sc hit was from a muon and
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not a beam-electron or otherwise,
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\item {\bf Muon pile-up.} Ensures the detected hit is definitely from the right
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muon, important when studying the timing of the processes.
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\item {\bf Energy cuts on thick and thin.}
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\end{itemize}
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Of the data taken during R2013, the two aluminium datasets (Al50 and Al100)
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have been studied the most. Additionally, data was also taken using one of the
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detectors as the target itself which gives additional information as to the
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stopping distribution and acceptances. This silicon dataset (ActiveSi) has only been
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partially analysed at this stage. Table \ref{tab:ChargedParticleDatasets} shows
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a summary of the datasets analysed.
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\begin{table}[htbp]
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\centering
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\caption{Status of the charged particle analysis for different datasets}
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\begin{tabular}{p{0.2\textwidth}p{0.7\textwidth}}
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\addlinespace
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\toprule
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\bf Dataset & \bf Analysis status and approach \\ %[0.5ex]
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\midrule
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Al100 & Fully unfolded \\
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\addlinespace
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Al50 & Spectrum at detector, comparison to MC using Al100 unfolded spectrum \\
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\addlinespace
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Active SiR2 & Spectrum at detector but with large background from lack of back wall shielding. Requires additional Active Target coincidence \\
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\bottomrule
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\end{tabular}
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\label{tab:ChargedParticleDatasets}
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\end{table}
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Possible backgrounds to the analysis come from muons scattering into the
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detector and stopping in the front face of the thin silicon, random coincidences
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between events in the thick and thin detectors, and waveform pile-up caused by
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two or more less energetic particles arriving at the same time.
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Muons stopping in the front of the thin silicon are an issue since those that
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capture on a silicon nucleus in the detector will emit charged particles which
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could---if they pass through the thin and stop in the thick---overlap with the
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distribution of the charged particles coming from the target. Since the
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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
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there is only 5\% contamination at maximum.
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