45 lines
2.3 KiB
TeX
45 lines
2.3 KiB
TeX
%The first run of the AlCap experiment was performed at the $\pi$E1 beam line
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%area, PSI from November 26 to December 23, 2013. The goal of the run was to
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%measure protons rate and their spectrum following muon capture on aluminium.
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The low energy muons from the $\pi$E1 beam line were stopped in thin aluminium
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and silicon targets, and charged particles emitted were measured by two pairs
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of silicon detectors inside of a vacuum vessel
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(\cref{fig:alcap_setup_detailed}). A stopped muon event is defined by
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a group of upstream detectors and a muon veto plastic scintillator.
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The number of stopped muons is monitored by a germanium detector placed outside
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of the vacuum chamber. In addition, several plastic scintillators were used to
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provide veto signals for the silicon and germanium detectors.
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\begin{figure}[btp]
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\centering
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\includegraphics[width=0.55\textwidth]{figs/alcap_setup_detailed}
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\caption{AlCap detectors: two silicon packages inside the vacuum vessel,
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muon beam detectors including plastic scintillators and a wire chamber,
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germanium detector and veto plastic scintillators.}
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\label{fig:alcap_setup_detailed}
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\end{figure}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\subsubsection{Muon beam}
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\label{ssub:muon_beam}
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%\Cref{fig:alcap_setup_detailed} shows the experimental setup. The muon
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%beam enters from the right of the image and hits the target, which is
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%placed at the center of the vacuum chamber and orientated at 45
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%degrees to the beam axis.
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%In order to define
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%stopped muon events, four muon counters are used: a 500~\rmmu m thick
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%scintillator muon trigger counter (\rmmu SC); a muon anti-coincidence
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%counter (\rmmu SCA) surrounding the trigger counter with a hole of 35
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%mm diameter to define the beam radius; and a multiwire proportional
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%chamber (\rmmu PC) that uses 24 X wires and 24 Y wires with at 2 mm
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%intervals. This detector system belongs to the MuSun experiment and
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%was well tuned in advance. A muon veto counter (\rmmu Ve) is placed
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%at the downstream end of the chamber and is used to reject muons that
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%pass through the stopping target.
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One of the main requirements of the AlCap experiment was a muon beam
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with narrow momentum bite in order to achieve a high fraction of
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stopping muons in the very thin targets. The actual set up used in the Run
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2013 was: muon momentum from \SIrange{28}{45}{\MeV\cc} and momentum spread of
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3\% FWHM.
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