75 lines
3.9 KiB
TeX
75 lines
3.9 KiB
TeX
\chapter{Discussions}
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\label{cha:discussions}
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\section{Thick aluminium target measurement}
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\label{sub:active_target_measurement}
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With a thick and active silicon target, I have tried to reproduce an existing
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result from Sobottka and Wills~\cite{SobottkaWills.1968}. This is important in
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giving confidence in our experimental method. The idea is the same as that of
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the old measurement, where muons were stopped inside a bulk active target and
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the capture products were measured. Due to the limitation of the
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currently available analysis tool, a direct comparison with the result of
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Sobottka and Wills is not practical at the moment.
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But a partial comparison is available for a part of the spectrum from 8 to
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10~MeV, where my result of $(1.22 \pm 0.19) \times 10^{-2} $ is consistent with
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the derived value $(1.28\pm0.19)\times10^{-2}$ from the paper of Sobottka and
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Wills. The agreement was partly because of large error bars in both results.
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In my part, the largest error came from the uncertainty on choosing the
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integration window. This can be solved with a more sophisticated pulse
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finding/calculating algorithm so that the contribution of muons in the energy
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spectrum can be eliminated by imposing a cut in pulse timing. The
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under-testing pulse template fitting module could do this job soon.
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The range of 8--10~MeV was chosen to be large enough so that the uncertainty of
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integration window would not to be too great; and at the same time be small
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enough so the protons (and other heavier charged particles) would not escape
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the active target. This range is also more convenient for calculating the
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partial rate from the old paper of Sobottka and Wills.
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% section protons_following_muon_capture_on_silicon (end)
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\section{Thin silicon target measurement}
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\label{sub:thin_and_passive_target_measurement}
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The charged particles in the low energy region of 2.5--8~MeV were measured by
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dE/dx method. The particle identification was good in lower energy part, but
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losing its resolution power as energy increases. The current set up could do
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the PID up to about 8~MeV for protons. This energy range is exactly the
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relevant range to the COMET experiment (Figure~\ref{fig:proton_impact_CDC}).
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In that useful energy range, the analysis showed a good separation of protons
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from other heavy charged particles. The contribution of protons in the total
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charged particles is 87\%. This is the high limit only since the heavier
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particles at this energy range are most likely to stopped in the thin
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detectors. More statistic would be needed to estimate the contributions from
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other particles.
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The effective emission rate of protons per muon capture in this measurement is
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4.20\%, with a large uncertainty contribution comes from limitation of the
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timing determination. The spectral integral in the region 2.5--8~MeV on
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Figure~\ref{fig:sobottka_spec} is about 70\% of the spectrum from 1.4 to
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26~\MeV, and corresponds to an emission rate of about 10\% per muon capture.
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The two figures are not in disagreement.
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In order to have a better comparison, a correction or unfolding for energy
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loss and more MC simulation study are needed. I am on progress of these study.
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% subsection thin_and_passive_target_measurement (end)
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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\section{Aluminium target measurement}
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\label{sec:aluminium_target_measurement}
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The proton emission rate was derived as 2.37\%, but the problem on the SiL1-1
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channel was not solved yet. One possible cause is the muons captured on other
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lighter material inside the chamber. More investigation will be made on this
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matter.
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The rate of 2.37\% on aluminium appears to be smaller on that of silicon but
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the two results are both effective rates, modified by energy loss inside the
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target. Unfolding and MC study for the correction are ongoing.
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% section aluminium_target_measurement (end)
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
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% chapter discussions (end)
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