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@@ -83,6 +83,6 @@ sensitivities. Details of the study on proton emission are described in
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Chapters~\ref{cha:alcap_phys},~\ref{cha:the_alcap_run_2013},~\ref{cha:data_analysis}:
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Chapters~\ref{cha:alcap_phys},~\ref{cha:the_alcap_run_2013},~\ref{cha:data_analysis}:
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physics, method, experimental set up, data analysis. The results and impacts of
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physics, method, experimental set up, data analysis. The results and impacts of
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the study on COMET Phase-I design is discussed in
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the study on COMET Phase-I design is discussed in
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Chapter~\ref{cha:discussions}.
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Chapter~\ref{cha:results_and_discussions}.
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% chapter introduction (end)
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% chapter introduction (end)
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@@ -343,9 +343,9 @@ calculated as:
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where $\Delta E_{\textrm{meas.}}$ is energy deposition measured by the thin
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where $\Delta E_{\textrm{meas.}}$ is energy deposition measured by the thin
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silicon detector by a certain proton at energy $E_i$, $\Delta E_i$ and
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silicon detector by a certain proton at energy $E_i$, $\Delta E_i$ and
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$\sigma_{\Delta E}$ are the expected and standard deviation of the energy loss
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$\sigma_{\Delta E}$ are the expected and standard deviation of the energy loss
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caused by the proton calculated by MC study. A threshold is set to extract
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caused by the proton calculated by MC study. A threshold is set at \num{1E-4} to
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protons at 0.011 (equivalent to $3\sigma_{\Delta E}$), the band of protons is
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extract protons, the resulted band of protons is shown in
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shown in (\cref{fig:al100_protons}).
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(\cref{fig:al100_protons}).
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\begin{figure}[htb]
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\begin{figure}[htb]
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\centering
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\centering
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\includegraphics[width=0.47\textwidth]{figs/al100_protons}
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\includegraphics[width=0.47\textwidth]{figs/al100_protons}
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@@ -510,9 +510,15 @@ The proton emission rate in the range from \SIrange{4}{8}{\MeV} is therefore:
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The total proton emission rate can be estimated by assuming a spectrum shape
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The total proton emission rate can be estimated by assuming a spectrum shape
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with the same parameterisation as in \eqref{eqn:EH_pdf}. The fit parameters
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with the same parameterisation as in \eqref{eqn:EH_pdf}. The fit parameters
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are shown in . With such parameterisation, the integration in
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are shown in \cref{fig:al100_parameterisation}. With such parameterisation, the
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range from \SIrange{4}{8}{\MeV} is 51\% of the total number of protons. The
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integration in range from \SIrange{4}{8}{\MeV} is 51\% of the total number of
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total proton emission rate is therefore $3.5\times 10^{-2}$.
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protons. The total proton emission rate is therefore $3.5\times 10^{-2}$.
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\begin{figure}[htb]
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\centering
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\includegraphics[width=0.85\textwidth]{figs/al100_parameterisation}
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\caption{Fitting of the unfolded spectra.}
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\label{fig:al100_parameterisation}
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\end{figure}
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\subsection{Uncertainties of the emission rate}
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\subsection{Uncertainties of the emission rate}
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\label{sub:uncertainties_of_the_emission_rate}
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\label{sub:uncertainties_of_the_emission_rate}
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@@ -2,13 +2,71 @@
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\label{cha:results_and_discussions}
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\label{cha:results_and_discussions}
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\section{Verification of the experimental method}
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\section{Verification of the experimental method}
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\label{sec:verification_of_the_experimental_method}
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\label{sec:verification_of_the_experimental_method}
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\subsection{Number of stopped muons calculation}
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\subsection{Number of stopped muons normalisation}
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\label{sub:number_of_stopped_muons_normalisation}
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\label{sub:number_of_stopped_muons_normalisation}
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The number of stopped muons calculated from the muonic X-ray spectrum is shown
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to be consistent with that calculated from the active target spectrum. This
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proves the validity of normalisation using muon X-ray measurement.
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\subsection{Particle identification and unfolding}
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\subsection{Particle identification and unfolding}
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\label{sub:particle_identification_and_unfolding}
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\label{sub:particle_identification_and_unfolding}
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The particle identification using specific energy loss using cut on
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likelihood probability is shown in
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\cref{sub:event_selection_for_the_passive_targets}. Since the distribution of
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$\Delta E$ at a given $E$ is not Gaussian, the fraction of protons that do not
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make the cut is 0.5\%, much larger than the threshold at \num{1E-4}. However,
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that missing fraction is small compared to the statistical uncertainty of the
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measurement (2.3\%) so the threshold is sufficient.
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The observed spectra on the two silicon arms reflect the muon stopping
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distribution discussed in \cref{sub:momentum_scan_for_the_100_} where more
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muons stopped at the downstream side of the target. The proton yields
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calculated from two arms are consistent with each other, and show that the muon
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stopping distribution used to generate the response matrices is reasonable.
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\section{Emission rate of protons and the COMET Phase I's CDC}
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\section{Emission rate of protons and the COMET Phase I's CDC}
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\label{sec:emission_rate_of_protons_and_the_comet_phase_i_s_cdc}
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\label{sec:emission_rate_of_protons_and_the_comet_phase_i_s_cdc}
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The proton emission rate from the 100-\si{\um} aluminium target is
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$(3.5 \pm 0.2)$\%. This rate is significantly larger than the calculation rate
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of 0.97\% by Lifshitz and Singer~\cite{LifshitzSinger.1978, LifshitzSinger.1980}.
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The $(\mu^-,\nu p):(\mu^-,\nu pn)$ ratio is then roughly 1:1, not 1:6 as in
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\eqref{eqn:wyttenbach_ratio}.
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The rate smaller that the proton emission rate from silicon of
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5.3\%~\cite{Measday.2001} which is expected since an odd-odd nucleus as
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$^{28}$Al is less stable than an even-odd one.
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For the COMET Phase I experiment, the emission rate of 3.5\% is about 5 times
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smaller than the figure using to design the CDC. The measured spectrum shape
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peaks around \SI{4}{\MeV} rather than \SI{2.5}{\MeV} in the silicon
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spectrum(\cref{fig:sobottka_spec}). Therefore the proton hit rate on the CDC
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should be smaller than the current estimation.
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The CDC proton hit rate is calculated by a toy MC study. The protons with the
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energy spectrum as the parameterisation in \cref{sub:proton_emission_rate} are
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generated inside the COMET's muon stopping targets which are 17
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200-\si{\um}-thick aluminium discs. A proton absorber made of CFRP is placed
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\SI{5}{\cm} far from the inner wall of the CDC.
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A muon stopping rate of \SI{1.3E9}{\Hz} is assumed as in the COMET Phase I's
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TDR. The number of proton emitted is then $\num{1.3E9} \times 0.609 \times
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0.035 = \SI{2.8E7}{\Hz}$. The hit rates on a single cell in the inner most
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layer due to these protons with
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different absorber thickness are shown in \cref{tab:proton_cdc_hitrate}.
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\begin{table}[htb]
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\begin{center}
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\begin{tabular}{l r}
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\toprule
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\textbf{Absorber thickness} & \textbf{Hit rate}\\
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\midrule
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\SI{1}{\mm} & \SI{2}{\Hz}\\
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\SI{0.5}{\mm} & \SI{126}{\Hz}\\
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\SI{0}{\mm} & \SI{1436}{\Hz}\\
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\bottomrule
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\end{tabular}
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\end{center}
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\caption{CDC proton hit rates}
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\label{tab:proton_cdc_hitrate}
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\end{table}
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The proton hit rate even without the absorber is only \SI{1.4}{\kHz}, much
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smaller than the current estimation of \SI{11}{\kHz} (using 1-mm-thick
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absorber). Therefore a proton absorber is not needed for the COMET Phase I's
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CDC.
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@@ -29,13 +29,14 @@ for the COMET experiment}
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\end{frontmatter}
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\end{frontmatter}
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\mainmatter
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\mainmatter
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%\input{chapters/chap1_intro}
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\input{chapters/chap1_intro}
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%\input{chapters/chap2_mu_e_conv}
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\input{chapters/chap2_mu_e_conv}
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%\input{chapters/chap3_comet}
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\input{chapters/chap3_comet}
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%\input{chapters/chap4_alcap_phys}
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\input{chapters/chap4_alcap_phys}
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%\input{chapters/chap5_alcap_setup}
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\input{chapters/chap5_alcap_setup}
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\input{chapters/chap6_analysis}
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\input{chapters/chap6_analysis}
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%\input{chapters/chap7_results}
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\input{chapters/chap7_results}
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%\input{chapters/chap8_conclusions}
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\begin{backmatter}
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\begin{backmatter}
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\input{chapters/backmatter}
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\input{chapters/backmatter}
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