add r15a_xray paper

r15a_xray/tex/abstract.tex

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+\begin{abstract}
+  Abstract
+\end{abstract}

r15a_xray/tex/analysis.tex

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+\section{Data analysis}
+

r15a_xray/tex/intro.tex

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+\section{Introduction}
+Why are we even doing this measurement? Here is a very thorough study~\cite{Zinatulina2019}

r15a_xray/tex/results.tex

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+\section{Results and discussions}
+

r15a_xray/tex/setup.tex

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+\section{Experimental setup}
+\label{sec:experimental_set_up}
+This measurement is part of the AlCap experiment done at PSI, Switzerland.
+The 2015 summer run focused on the detection of neutral particles: low energy
+X-ray, gamma ray and neutron emission after the muon is captured by the
+nucleus. 
+
+The X-rays and gamma rays of interest are:
+\begin{itemize}
+  \item muonic $2p-1s$ transition in aluminum: \SI{346.8}{\kilo\eV}
+  \item \SI{843.7}{\kilo\eV} gamma from the $\beta^-$ decay of \ce{^{27}Mg}
+    (half-life: \SI{9.46}{\min})
+  \item \SI{1808.7}{\kilo\eV} gamma from the first excited state of
+    \ce{^{26}Mg}
+\end{itemize}
+
+Low momentum muons (less than \SI[]{40}{\mega\eVperc}) were stopped in
+a target after passing a muon counter
+(\SI{60}{\mm}$\times$\SI{60}{\mm}$\times$\SI{0.5}{\mm} plastic scintillator). 
+% Upstream from the muon counter, a 
+% \SI{10}{\cm} $\times$ \SI{10}{\cm}  $\times$ \SI{0.6}{\cm} scintillator with
+% a \SI{40}{\mm} diameter hole cut in the center acted as a  beam defining
+% veto counter to the incoming muon beam.
+There were two 5"$\times$2" liquid scintillator BC501a detectors setup on the
+beam right to detect neutrons. For gamma spectrum analysis and normalization
+we used an HPGe detector installed on the beam left. In addition, a \ce{LaBr3}
+scintillator was also tested if it would be suitable to use in the STM. A 25
+LYSO crystal array was placed downstream of the target beam left to observe
+high energy photons emitted.
+
+Two identical preamplifier outputs from the HPGe detector were fed into: (a)
+a timing filter amplifier for timing information, and (b) a spectroscopy
+amplifier for energy information. The timing pulses were read out by a 14-bit
+500-MS/s desktop digitizer(CAEN DT5730). In order to accommodate both low
+energy X-rays and relatively high energy gamma rays, we used two channels from
+the spectroscopy amplifier with different gain settings: (a) a lower gain
+channel for photons up to \SI{6.5}{\mega\eV}; and (b) a higher gain channel for
+photons up to \SI{2.5}{\mega\eV}. These channels were read out by a 14-bit
+100-MS/s VME digitizer (CAEN V1724).
+
+The \ce{LaBr3} crystal is coupled with a photomultiplier, of which output
+pulses were large enough so no further amplification was needed. This channel
+is read out with the DT5730.
+
+% Detectors' outputs were read out using waveform digitizers. We used a 14-bit
+% 100-MS/s VME digitizer (CAEN V1724) to record energy signals from
+% HPGe and \ce{LaBr3} detectors. There were two energy outputs from the HPGe
+% detector with different gain settings: (a) low gain channel for photons up to
+% \SI{6.5}{\mega\eV}; and (b) high gain channel for photons up to
+% \SI{2.5}{\mega\eV}. The timing signals from these detectors, and signals from
+% plastic and liquid scintillators were fed into a faster digitizer, namely
+% a 14-bit 500-MS/s desktop digitizer (CAEN DT5730).
+% These fast timing channels
+% were also read out using a multihit TDC (CAEN V1290A) as a back up solution.
+% All digitizers and TDC were synchronized by an external master clock.
+
+Experimental layout  is shown  in \cref{fig:R2015a_setup}.
+\begin{center}
+  \begin{figure}[tbp]
+    \centering
+    \includegraphics[width=0.70\textwidth]{figs/r15a_setup_photo}
+    \caption{Layout of the AlCap 2015 summer run. Muons entered from the top of
+      the image. The LYSO detector is not visible in this image, which is
+      located further out in the bottom of the image.} 
+    \label{fig:R2015a_setup}
+  \end{figure}
+\end{center}
+
+There were several runs with different targets made of aluminum, titanium,
+lead, water. All targets were sufficiently thick to stop the muon beam with
+momenta up to \SI{40}{\mega\eVperc}.
+
+