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Update APPC2013 proceeding, according to reviewer's request

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2013-08-27 11:10:23 +09:00
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APPC2013/abstract/abstract.tex
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@@ -124,7 +124,7 @@ Using the J-PARC proton beam and the pion capture by
a solenoidal field, COMET will have a single event sensitivity 10,000 times a solenoidal field, COMET will have a single event sensitivity 10,000 times
better than the current limit. The COMET collaboration has taken a phased better than the current limit. The COMET collaboration has taken a phased
approach in which the first phase, COMET Phase-I [3], starts in 2013 and approach in which the first phase, COMET Phase-I [3], starts in 2013 and
initial data taking in around 2016. This paper provides some highlights among initial data taking in around 2017. This paper provides some highlights among
ongoing R\&D activities. ongoing R\&D activities.
%Charged lepton flavor violation (CLFV) has attracted much attention from %Charged lepton flavor violation (CLFV) has attracted much attention from
@@ -157,18 +157,18 @@ ongoing R\&D activities.
~\\ ~\\
~[1] Y.~Kuno {\it et al.} (COMET collaboration), ``A Experimental ~[1] D.~Bryman (The COMET collaboration): ``An experimental
Search for Lepton Flavor Violating \muec Conversion at Sensitivity of search for lepton flavor violating $\mu^- - e^-$ conversion at sensitivity of
$10^{-16}$ with A Slow-Extracted Bunched Proton Beam'', J-PARC Proposal, 2007 $10^{-16}$ with a slow-extracted bunched proton beam'', J-PARC Proposal,
and J-PARC Conceptual Design Report, 2009.\\ 2007. \\
~[2] W.~Bertl {\it et al.} (SINDRUM-II collaboration), ``A search for $\mu
- e$ conversion in muonic gold'', The European Physical Journal C 47 (2006) ~[2] W.~Bertl (SINDRUM-II collaboration): Eur. Phys. J. C \textbf{47} (2006)
337-346.\\ 337-346.\\
~[3] Y.~Kuno {\it et al.} (COMET collaboration), ``Letter of ~[3] R. Akhmetshin (The COMET collaboration): ``Experimental
Intent of Phase-I for the COMET Experiment at J-PARC'', unpublished, March proposal for Phase--I of the COMET experiment at J-PARC'', KEK/J-PARC-PAC
2012. 2012-10.
%%% %%%

94
APPC2013/proceeding/proceeding.tex
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@@ -53,29 +53,30 @@ This is an unobservably tiny
branching ratio so that any experimental evidence of CLFV would be a clear branching ratio so that any experimental evidence of CLFV would be a clear
sign of new physics beyond the SM. sign of new physics beyond the SM.
Among CLFV processes, one of the most prominent one is One of the most prominent CLFV processes is
a process of coherent muon-to-electron conversion ($\mu a process of coherent muon-to-electron conversion ($\mu
- e$ conversion) in the field of a nucleus: \muecaz. $\mu - e$ conversion would - e$ conversion) in the field of a nucleus: \muecaz. When muons are stopped in
occur in the following manner. Stopped muons are quickly captured by atoms a target, they are quickly
($~10^{-10}$ s) and cascade down to the 1S orbitals. There, they can undergo: captured by atoms ($~10^{-10}$ s) and cascade down to the 1S orbitals. There,
they can undergo:
(a) ordinary decay, (b) weak capture, $\mu^- p \rightarrow \nu_\mu n$, or (c) (a) ordinary decay, (b) weak capture, $\mu^- p \rightarrow \nu_\mu n$, or (c)
$\mu - e$ conversion, \muec. The last of these reactions is a CLFV process $\mu - e$ conversion, \muec. The last of these reactions is a CLFV process
where lepton flavor numbers, $L_\mu$ and $L_e$, are violated by one unit. where lepton flavor numbers, $L_\mu$ and $L_e$, are violated by one unit.
The $\mu - e $ conversion is attractive both from theoretical and experimental The $\mu - e $ conversion is attractive both from theoretical and experimental
points of view. Many extensions of the SM predict that it would has sizeable points of view. Many extensions of the SM predict that it would has sizeable
branching ratio~\cite{altman}, one possible supersymmetric contribution to the branching ratio~\cite{altman}. One possible supersymmetric contribution to the
$\mu - e$ conversion is shown in Fig.~\ref{fig:susy_contr}. Experimentally, the $\mu - e$ conversion is shown in Fig.~\ref{fig:susy_contr}. Experimentally, the
simplicity and distintive signal, a mono-energetic electron of energy: simplicity and distintive signal, a mono-energetic electron of energy $E_{e}$:
\[ \[
E_{mec} = m_{\mu} - B_{\mu}(Z, A) - R(A) \simeq \textrm{105 MeV}, E_{e} = m_{\mu} - B_{\mu}(Z, A) - R(A) \simeq \textrm{105 MeV},
\] \]
where $m_\mu$ is the muon mass, $B_\mu(Z, A)$ is the muonic atom binding where $m_\mu$ is the muon mass, $B_\mu(Z, A)$ is the muonic atom binding
energy, and $R(A)$ is the nuclear recoil energy, allow experimental searches energy, and $R(A)$ is the nuclear recoil energy, allow experimental searches
without accidentals and extremely high rates. As a result, one of the best without accidentals and thus in extremely high rates. As a result, one of the
limit of CLFV searches comes from a search for $\mu - e$ conversion in muonic best upper limits of CLFV searches comes from a search for $\mu - e$ conversion
gold done by in muonic gold done by the SINDRUM--II collaboration:
the SINDRUM--II collaboration: \sindrumlimit~\cite{sindrumii}. \sindrumlimit~\cite{sindrumii}.
\begin{figure}[tbh] \begin{figure}[tbh]
\centering \centering
@@ -91,31 +92,32 @@ $10^{-17}$}
\subsection{The COMET experiment} \subsection{The COMET experiment}
At the Japan Proton Accelerator Research Complex (J-PARC), an experiment to At the Japan Proton Accelerator Research Complex (J-PARC), an experiment to
search for \muec~conversion, which is called COMET (COherent Muon to Electron search for \muec~conversion, which is called COMET (COherent Muon to Electron
Transition) has been proposed~\cite{comet07}. The experiment received Stage--1 Transition), has been proposed~\cite{comet07}. The experiment received Stage--1
approval in approval in
2009. Utilising a proton beam of 56 kW from the 2009. Utilising a proton beam of 56 kW (8 GeV $\times$ 7 $\mu$A) from the
J-PARC main ring, the COMET aims for a single event sensitivity of $3 \times J-PARC main ring, the COMET aims for a single event sensitivity of $3 \times
10^{-17}$, which is 10000 times better than the current best 10^{-17}$, which is 10000 times better than the current best
limit at SINDRUM--II. limit at SINDRUM--II. As of April 2013, the COMET collaboration has 117
members in 27 institutes from 12 countries.
The COMET experiment is designed to be carried out at the Nuclear and Particle The COMET experiment is designed to be carried out at the Hadron
Experimental Hall (NP Hall) using a bunched proton beam that is Experimental Facility using a bunched proton beam that is
slowly-extracted from the J-PARC main ring. The experimental set-up consists of slowly-extracted from the J-PARC main ring. The experimental set-up consists of
a dedicated proton beam line, a muon beam transport section, and a detector a dedicated proton beam line, a muon beam transport section, and a detector
section. The muon beam section is composed of a superconducting pion capture section. The muon beam section is composed of superconducting magnets: pion
solenoid with high magnetic field. The detector section has muon stopping capture solenoid and a pion/muon transport solenoid. The
targets, an electron transport beam line for $\mu - e$ conversion signals, detector section has a multi-layered muon stopping target, an electron
transport beam line for $\mu - e$ conversion signals,
followed by detector systems. followed by detector systems.
\subsection{Staging approach at the COMET} \subsection{Staging approach at the COMET}
The COMET collaboration, which has 117 collaborators in 27 institutes from The COMET collaboration has adopted a staging approach with two
12 countries as of April 2013, has adopted a staging approach with two
phases~\cite{comet12}. COMET Phase--I is scheduled to phases~\cite{comet12}. COMET Phase--I is scheduled to
have an engineering run in 2016, followed by a physics run in 2017. Phase--I have an engineering run in 2016, followed by a physics run in 2017. Phase--I
should achieve a sensitivity should achieve a sensitivity
of $3 \times 10^{-15}$, 100 times better than that of SINDRUM--II; while of $3 \times 10^{-15}$, 100 times better than that of SINDRUM--II; while
Phase--II will reach a sensitivity of $3 \times 10^{-17}$, which is Phase--II will reach a sensitivity of $2.6 \times 10^{-17}$, which is
comparable to the Mu2e project at Fermilab~\cite{mu2e08}. competitive with the Mu2e project at Fermilab~\cite{mu2e08}.
A schematic layout of the COMET experiment with its two phases is A schematic layout of the COMET experiment with its two phases is
shown in Fig.~\ref{fig:comet_phase1}, and a schedule for two phases is shown in shown in Fig.~\ref{fig:comet_phase1}, and a schedule for two phases is shown in
Fig.~\ref{fig:sched}. Fig.~\ref{fig:sched}.
@@ -129,7 +131,7 @@ Fig.~\ref{fig:sched}.
\begin{figure}[tbh] \begin{figure}[tbh]
\centering \centering
\includegraphics[width=\textwidth]{figs/sched} \includegraphics[width=0.8\textwidth]{figs/sched}
\caption{The anticipated schedule of the COMET experiment.} \caption{The anticipated schedule of the COMET experiment.}
\label{fig:sched} \label{fig:sched}
\end{figure} \end{figure}
@@ -142,32 +144,32 @@ COMET Phase--I has two major goals:
\times 10^{-15}$. \times 10^{-15}$.
\end{itemize} \end{itemize}
In order to realized the goals, COMET Phase--I proposes to have two systems of In order to realize the goals, COMET Phase--I proposes to have two systems of
detector. A straw tube detector and electromagnetic calorimeter will be used detector. A straw tube detector and an electromagnetic calorimeter will be used
for the background study. For the $\mu-e$ conversion search, a cylindrical for the background study. For the $\mu-e$ conversion search, a cylindrical
drift chamber (CDC) will be built. drift chamber (CDC) will be built.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\section{Status of the COMET experiment} \section{Status of the COMET experiment}
The COMET collaboration is working very hard to realize the schedule with the The COMET collaboration is working very hard toward the
physics run in 2017. Some R\&D activities are hightlighted as follow. physics run in 2017. Some R\&D activities are hightlighted as follows.
\subsection{COMET beam line and experimental hall} \subsection{COMET beam line and experimental hall}
Budget for construction of the COMET beam line and experimental hall has been Budget for construction of the COMET beam line and experimental hall has been
approved. Construction has been started in 2013 and is expected to be completed approved. Construction has been started in 2013 and is expected to be completed
by spring 2015. Production of coils for superconducting magnets will begin in by spring 2015. Production of coils for superconducting magnets will begin in
July, 2013. Design of radiation shielding and pion production target are in July, 2013. Design of the radiation shielding and the pion production target
progress. are in progress.
\subsection{R\&D for detectors} \subsection{R\&D for detectors}
\subsubsection{Cylindrical drift chamber} \subsubsection{Cylindrical drift chamber}
The CDC is a detector dedicated for COMET Phase--I to maximize the experimental The CDC is a detector dedicated for COMET Phase--I to maximize the experimental
sensitivity for the $\mu-e$ conversion search. A prototype CDC would be ready sensitivity for the $\mu-e$ conversion search. A prototype CDC will be ready
for testing at Osaka University in September, 2013. Designing for the real for testing at Osaka University in September, 2013. Designing for the real
detector is ongoing based on simulation study and experiments with a test detector is ongoing based on simulation studies and experiments with a test
chamber and test readout boards. chamber and test readout boards.
One designing issue with the CDC is its single hit rate would be dominated by One designing issue with the CDC is that its single hit rate would be dominated
protons emitted after muons are captured in the target. The lack of by protons emitted after muons are captured in the target. The lack of
experimental data on protons from Al target makes it difficult to optimize experimental data on protons from Al target makes it difficult to optimize
the inner wall of the CDC to achieve best momentum resolution. In order to the inner wall of the CDC to achieve best momentum resolution. In order to
provide input for this optimization, a dedicated provide input for this optimization, a dedicated
@@ -179,14 +181,15 @@ a joint effort between COMET and Mu2e.
The straw tube tracker for background study in COMET Phase--I is being The straw tube tracker for background study in COMET Phase--I is being
developed with expertise from JINR, Russia group in NA62 experiment. A KEK-JINR developed with expertise from JINR, Russia group in NA62 experiment. A KEK-JINR
collaboration has been formed to produce a prototype tracker. R\&D for this collaboration has been formed to produce a prototype tracker. R\&D for this
prototype would be completed in 2013. Design works and construction of the real prototype will be completed in 2013. Design works and construction of the real
detector is ongoing. detector is ongoing.
\subsubsection{Electromagnetic calorimeter} \subsubsection{Electromagnetic calorimeter}
An electromagnetic calorimeter will be used in the COMET Phase--II as a trigger An electromagnetic calorimeter will be used in the COMET Phase--II as a trigger
detector that triggers on 105 MeV electrons. Currently, two types of crystal detector that triggers on 105 MeV electrons, as well as in the Phase--I for the
background study. Currently, two types of crystal
are considered for this calorimeter: GSO and LYSO. Beam tests of calorimeter are considered for this calorimeter: GSO and LYSO. Beam tests of calorimeter
prototypes with APD readout are underway. The choice of crystal would be made prototypes with APD readout are underway. The choice of crystal will be made
in a few months. A prototype electronics system for the detector has been in a few months. A prototype electronics system for the detector has been
developed by BINP, Novosibirsk, Russia group, and is being evaluated in the developed by BINP, Novosibirsk, Russia group, and is being evaluated in the
beam tests at J-PARC. beam tests at J-PARC.
@@ -195,18 +198,23 @@ beam tests at J-PARC.
Software used to simulate and analyse data is crucial to the success of the Software used to simulate and analyse data is crucial to the success of the
COMET experiment. The COMET software group has set up a new software framework COMET experiment. The COMET software group has set up a new software framework
called ICEDUST (Integrated COMET Experiment Data User Software Toolkit). The called ICEDUST (Integrated COMET Experiment Data User Software Toolkit). The
framework includes an improved simulation for the experiment. It also framework includes an improved simulation for the experiment. Some improvements
are: the ability to run the simulation on a computing grid for large simulation
data production, and an optimized
beam line with a realistic magnetic field map from the manufacturer of the
superconducting magnets. The ICEDUST also
has modules to perform calibration, reconstruction and analysis of both has modules to perform calibration, reconstruction and analysis of both
Monte-Carlo outputs and experimental data in a unified way. Documentations and Monte-Carlo outputs and experimental data in a unified way. Documentations and
implementations of ICEDUST are underway. implementations of the ICEDUST are underway.
\section{Summary} \section{Summary}
The COMET (J-PARC E21) experiment is going to push the limit of experimental The COMET (J-PARC E21) experiment is going to push the limit of experimental
searches for CLFV $\mu-e$ conversion process, a very promising probe for new searches for CLFV $\mu-e$ conversion process, a very promising probe for new
physics beyond the SM. Heavy R\&D activities are ongoing to realize the physics physics beyond the SM.
run of its first stage, COMET Phase--I, in the year of 2017 with an immediate The first stage, COMET Phase--I, will improve the upper limit by two orders of
goal: two orders of magnitude improvement in the single event sensitivity magnitude to a single event sensitivity of $3\times10^{-15}$.
compares the the current best limit. Heavy R\&D activities are ongoing to realize the physics
run of the COMET Phase--I in the year of 2017.
%\appendix %\appendix
%\section{} %\section{}
% %