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\title[WG4]{Non-neutrino physics working group summary}

\author{J.-M. Poutissou\dag and K. Yoshimura\ddag}

\address{\dag\ TRIUMF,4004 Wesbrook Mall, Vancouver V6T 2A3 Canada}

\address{\ddag\ KEK-IPNS ,High Energy Accelerator Research Organization,Tsukuba,305-0801,Japan.}
\ead{jmp@triumf.ca}


\begin{abstract}
This summary covers the physics topics that could benefit from the unprecedented flux of muons produced
at the front end of the future neutrino factory. A selection of such opportunities were
presented at NuFact02 and their demands on beam properties were evaluated.
This summary will survey the rare muon decay experiments and the high precision measurements
 that could benefit from higher fluxes as well as 
some of the new programs that could use very large $\mu^{-}$ fluxes. A number of technological
developments relevant to the  neutrino  factories were also discussed.

\end{abstract}

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\section{Introduction}
The high intensity muon beams which will be developed for the neutrino factory provide unprecedented
opportunities in many field of muon research.These fields of science are very
 active today and
are contributing to the ideas behind the development of such high intensity muon
sources. As such they represent testing grounds for technologies to be used at the neutrino factories.
The physics motivations of these programs are quite enticing today and will provide
 for
the foreseeable future a strong base for muon science. This summary will focus on three main aspects
of muon science:

\begin{itemize}
\item The rare decay program on lepton flavor violation branches which requires
the maximum intensities possible

\item the high precision experiments which require a combination of high fluxes
but also very specific beam properties.
\item novel research presently limited by the low fluxes of specialized low energy negative muons.

\end{itemize}

 A survey of beam properties requirements was made during the meetings of the
 working group to provide some guidance for the accelerator group designing
 the front end of the neutrino factory. Some recent developments in muon beam technology
 were also reported and briefly mentioned  at
  the end of this report.
%\end{document}

%\subsection{previous related discussions}
A survey of several potentially interesting fields of research that could benefit
from a super muon source was made last year during a workshop organized by CERN at Trento\cite{n1}
and whose conclusions were reported at NuFact01 .
 During the NuFact02 working group 4  sessions ,an attempt was made to update 
the information
 gathered in the previous two workshops  aiming at providing bench mark 
requirements 
 for the muon sources to be examined by the accelerator builders at subsequent 
meetings.


\section{Rare decay program}

The physics motivation for doing research on rare muon decay processes like $ \mu
\rightarrow e\gamma $, $\mu \rightarrow e e e $ or $ \mu$N $\rightarrow $  e N conversion
has received a considerable boost when it was realized that supersymmetric models
naturally induce flavor lepton violation through the slepton sector of the theory.
Current experimental upper limits are already placing some constraints on the
parameter space of these theories. For a recent review of the field consult the
Kuno et al paper..\cite{n2} . In a recent turn of events ,it is now possible to induce
 flavor violation  via the
Majorana sector of neutrino mass matrix and the prediction for the muon rare decays
induced by the coupling to right handed neutrino linked to the observed oscillations
in the atmospheric and solar neutrino are within the reach of the current generation
of experiments. In Fig 1.  predictions for $\mu \rightarrow e\gamma $ are given for a range of right handed Majorana neutrino masses needed to get the range of 
$\Delta M^{2} $ derived from the solar and atmospheric neutrino oscillation 
data \cite{n3} . 
\begin{figure}
\begin{center}
\includegraphics[angle=90,width=\linewidth]{muegammatheory.ps}\\[0mm]
{\small \setlength{\baselineskip}{2.6ex}Fig. 1 Theoretical prediction for the $\mu\rightarrow e \gamma$ branching ratio for plausible value of  righthanded Majorana neutrino mass}

\end{center}
%\caption{\label{below} Theoretical prediction for the $/mu/rightarrow e \gamma$ branching ratio for plausible value of  righthanded majorana neutrino mass}
\end{figure} 
However high fluxes of muons are not the only requirements for mounting searches
 at the level of $ 10^{-15}$ or $ 10^{-17}$ branching ratios. To exploit these very large fluxes
 considerable sophistication must go into the triggering scheme and detector performance
 both in term of resolution to reduce the background and in terms of data
 acquisition capabilities. Unlike the situation with neutrino experiments,rare decay
 searches rely on identifying few events in a large background of events which pass
 the trigger requirements.
 Recent ideas about photon detection for example were described during the workshop
 which are to be incorporated in the PSI search for $ \mu \rightarrow $ e $ \gamma $ .
  Photon detection in a liquid Xenon detector promises to give high efficiency,good energy
  resolution  at 50 MeV and tracking capabilities. \cite{n4}.
  The ideas for detecting 105 MeV electrons from $\mu $ N $ \rightarrow $ e N
experiments within a narrow
  energy window are being simulated and will be incorporated in the Brookhaven effort for the MECO experiment\cite{n5}.

  In general, another requirement for these experiments is to have a time structure
  for the muons arriving at the experiment which matches the muon lifetime ( 1 to 10
  microsec between bursts) allowing for the observation of the decays while proton beam induced
  background is minimized.
  Consequently, rare decay searches require intensities in the range of $ 10^{12 }$
  muons/sec, a few percent energy spread to stop the muons in thin targets, and repetition rates
  in the MHz range.

 In Japan, these requirements led to the PRISM proposal which incorporates 
high muon fluxes ( from a superconducting capture solenoid around the 
production target), a small muon momentum spread ( from phase rotation in a FFAG ring) and low pion contamination ( from the  decay section and the 
selectivity of the FFAG)  \cite{n51}


\section{High precision experiments}
In a second series of talks, the status of current experiments on precision
 measurements of muon decay were reviewed: 
there are two efforts to improve the precision of the lifetime of positive 
muons,one a RAL and one at PSI. The interest here is to provide parts per 
million accuracy for the determination of the Fermi coupling constant, $G_{f}$.
 Two complementary determinations of the Michel parameters describing the 
decaying positron   energy and angular distribution on one hand (TWIST 
experiment at TRIUMF)
and its polarization vector components (PSI) on the other hand are starting to 
produce results. 
In these efforts, high intensity accelerators are used to provide specialized
 muon beams
with properties tailored to the specific measurements: ( beam emittance,beam 
absolute polarization, time structure to minimize pile-up of muons in the 
target ,etc..).

 The current measurements of the muon lifetime are aimed at reducing the error on 
$\tau_{\mu} $ to 2 picosec which translate on a 1 ppm error in $G_{f}$.
Two experiments were discussed; the RAL/RIKEN effort at ISIS \cite{n6} and the FAST collaborative effort at PSI \cite{n7} . A third program is also approved at PSI,the $\mu$LAN experiment

These experiments require large data samples ( $10^{12}$ events) over 10 muon lifetimes with careful considerations for multiple decays,residual polarization asymmetries
 and magnetic field induced spin rotations. Tracking and detector segmentations are used to fight the pile up of simultaneous muon decays. Stopped pions as a muon source or careful selection of depolarising target material are used to 
provide unpolarised muon samples.

The RIKEN/RAL collaboration presented a preliminary evaluation of their data corresponding to a 14 ppm measurement of $\tau_{\mu}$ and described the 
improvements being implemented to reach the 1 ppm goal.
 The FAST collaboration reported on their plans and described the detector under construction which allows for independent tracking of each muon event.

These measurements rely on very high counting rates and would benefit from a time structure providing sharp beam bunches at a 1 to 100 kHz rate.

 The determination of the MICHEL parameters provide a window of opportunity
 to explore physics beyond the V-A structure of the weak interaction. In the 
most general
derivative free, Lorentz invariant lagrangian formulation,these parameters can
 be expressed by linear combinations of all  coupling constants square which
 include both righhanded and lefthanded fermions and scalar, vector or tensor
 interactions. The current knowledge of the Michel parameters and the inverse
 neutrino electron charge current reaction cannot place severe constraints on
 the non V-A part of the interaction. This was reviewed by W.Fetscher\cite{n3.1} in the 
plenary part of the proceedings. The new TWIST experiment at TRIUMF is aimed at 
providing a $10^{-4}$ precision 
determination of the four parameters describing polarized muon decay  angular 
and momentum distribution.
 This could be used to limit for 

\begin{figure}
\begin{center}
\resizebox{10cm}{!}{\includegraphics[width=\linewidth]{twistreach.ps}}\\[0mm]
{\small \setlength{\baselineskip}{2.6ex}Fig. 2  Limits on right handed W mass and mixing from the TWIST experiment at TRIUMF }

\end{center}
%\caption{\label{below}Fig. 2  Limits on right handed W mass and mixing from the TWIST experiment at TRIUMF}
\end{figure}
 
example the  mass and mixing of the possible 
right handed sector in left right symmetric model in a complementary way to the
direct searches for right handed W at the hadron colliders (CDF,D0) see Fig 2. .


In a join session with the working group on neutrino oscillation theories, 
 Dr. Babu  presented a model of anomalous muon decay which could 
explain the 
LSND anomaly by allowing a branch to decay to two antineutrino \cite{n8}. 
The model is 
build to avoid lepton flavor violating decays. A possible signature of such a
 muon
 decay branch would be a reduction of the $ \rho $ Michel parameter from its 
V-A value of .75 to .7418 which should be seen in the TWIST experiment.

The TWIST experiment currently taking data at TRIUMF relies on specially 
prepared muon beam with high polarization, obtained by selecting muon 
originating from pion decaying on the surface of the production target .
 The high polarization is maintained during the transport of the muon to a 
stopping target located in center of a 2T solenoid which contains a set of
 52 low mass wire chambers to track the decaying positrons.
A $10^{-4}$ determination of the $P_{\mu}\xi $ parameter would constraint a 
righhanded W mass to $\geq$ 700GeV with very small mixing to its lefthanded 
partner.

 The PSI effort focused on the determination of the polarization vector components of the positron, In a recent series of measurement tight constraints have been 
obtained on $P_{L}$ the longitudinal component which is 1 in the standard model,$P_{T_{1}}$ and $P_{T_{2}}$ which are the transverse components respectively 
$
10^{-3}$ and 0 in the standard model .
$P_{T_{2}}$ is time reversal violating and a limit was obtained of $1.2 *10^{-3}$, a unique test of TRI in a purely leptonic system. $P_{T_{1}}$ can be related to the other parameter $\eta$ in the 
positron energy distribution and a new value compatible with zero was obtained:
$\eta = 0.0013 \pm 0.0008 $

 This experiment relied on a high polarization, a short beam burst which was 
synchronized to the cyclotron frequency and to the larmor rotation of the 
polarization vector to produce an ensemble of decaying muons in phase with 
each other.

In these programs of precision measurements of the MICHEL parameters, it is not
 obvious how the larger intensity of neutrino factories can be use to an 
advantage.


\section{Negative muon program}


During the proceedings of the working group, a number of possible programs 
making use of large
fluxes of negative muons were examined.
Amongst them muon catalyzed fusion is a
field that could be substantially enhanced by the availability of huge fluxes. 
Muon catalyzed fusion proceeds through the capture of a muon into a molecule
 with the subsequent fusion of the nuclei involved while the muon is released 
and can proceed to trigger further fusions during its lifetime. The efficacy
 of the process depends crucially on the capture probability, the fusion 
probability  of the muonic molecule formed and the release of the muon after 
fusion.
 
 During the last two decades considerable progress has been made in 
understanding
the basic molecular dynamics involved and resonances have been identified 
both theoretically and  experimentally for example in the D-T system.
To go beyond this basic research and identify the optimal conditions which
 could lead to practical applications will require higher intensities and
 higher energy
muons than are available at the present meson facilities. 
Dr. K.Nagamine\cite{n9} described the concept of fusion reactor vessels which 
could be 
used with high pressure mixtures of D-T. To increase the probability of 
fusions high temperatures and high pressure will most likely be required.
 Considerable studies of the optimal conditions will have to be done before a 
break even situation can be envisaged. This was reported by Dr.K.Ishida \cite{n10.1}

 Radioactive muonic ions could also be produced and the standard technique of 
determining the charge radii of nuclei could be available for very exotic 
nuclei
that can be produced at the new radioactive beam facilities.
 A concept project is under way at ISIS by the RIKEN collaboration using long 
lived ions
 that can be delivered to a target in which large fluxes of negative muons can be stopped.
 By relying on the fast and  effective transfer of the captured muons from a light target
 material to higher Z nuclei, the group is able to observe muonic X-rays of the unstable nuclei \cite{n10}.
For very short lived nuclei, very intense muon beams will be required.

 Muonic atom X-rays are very characteristic of the Z value of the nucleus. 
The capture probability is itself  Z-dependent. This can be use to do non 
destructive elemental analysis as was demonstrated in a pilot experiment by 
the RIKEN group 
at TRIUMF. By combining stopping distribution information from a tracking 
detector , 
and high energy X-rays analysis, one can conceive of powerful elemental 
analysis tool for application in medicine or other field of science.

  
    



\section{Other applications and new technologies}
 A further application of the high flux of muons available at the front end 
of a neutrino factory would be the development of very low energy muon beams
 which are 
of considerable interest for the condensed matter programs using the Muon
 spin rotation ( $\mu$SR ) technique.
 Currently low energy muons are produced by ionizing a muonium atom either 
thermally or via laser ionization.
 Such an intense low energy muon source could also be use at the front end of 
an accelerator system which would make use of the very small phase space of 
the source. Considerable improvements are needed to produce intense ultra low
 energy muons. The current source at PSI is limited to a few hundred muon per
 seconds\cite{n11}.
Recent progress has been made toward the development of high acceptance muon channels.
The DAI-OMEGA project \cite{n12} at the KEK booster delivered its first beam since the 
last NuFact01 meeting. It is a superconducting axial focusing channel with 
1sr solid angle. Several of the ideas considered for the front end of a 
neutrino factory are embedded in this channel. In particular the operation of a 
superconducting capture solenoid around a proton target is relevant to the
 neutrino factory muon source


\section{Conclusions}
The muon beam requirements  of the programs reviewed during the workshop 
have  been summarized in  table 1.

\begin{table}
\caption{\label{label} Muon beam requirements.}
%\begin{indented}
\begin{tabular}{@{}llllllllll}
 \br
           &    &Inten.& pulse & pulse &       &Mom. &     &     &     \\
 process   &  Q  & $\int_{0}^{10^{7}s}$ &width&interval&Energy&spread & purity&size&Pol   \\
           &      &          & (nsec)&(($\mu$sec)& (MeV) &  (\%) & && \\
\mr
$\mu$N$\rightarrow$eN'&   -  & $10^{21}$ &10-100&1-1000&$ \leq 20 $ &$ \leq 10$   &    &    &    n/a  \\ \hline
$\mu$N$\rightarrow$eN'&   -  & $10^{20}$ &10-100&1-1000& $\leq 20 $  &  3   &$10^{-15} (\pi)$&  cm &    n/a  \\ \hline
$\mu\rightarrow e \gamma$  &  +  & $10^{17}$ & DC & $\leq 1 $&  1  & $\leq 10 $ & $10^{-2}$(e) &  cm &  n/a    \\ \hline
$\tau_{\mu}$   &  +  & $10^{14}$  & $\sim 100 $ &30-100 &  4  & 1-10  &     &    &    depol  \\ \hline
$\tau_{\mu} (\pi)$ &  +  & $10^{14}$  &$ \sim 100 $ &30-100 &  4  & 1-10  &     &    & $\pi$ beam \\ \hline
Michel para. &  +  & $10^{16}$  & $\leq0.5$  & $\geq .02 $ &30-40  & 1-3  &     &    & 100\%  \\ \hline
Pol. para. &  +  & $10^{16}$  &$\leq 0.5$  & $\geq .02$ &30-40  & 1-3  &     &    & $ \sim 100$ \%   \\ \hline
  g-2      &  +/-  & $10^{15}$  & $\leq 50 $  & $\geq 1000$ &3100  &$10^{-2}$  &     &    & pol  \\ \hline
  edm      &  +/-  & $10^{16}$  & $\leq 50 $  & $\geq 1000$ &$\geq 1000 $ &$10^{-3}$  &     &    & pol  \\ \hline
$\mu$-atoms  &   -  & $10^{16}$  &$ \leq 100 $  & 100-1000 &1-4  &1 to 5  &$10^{-2}$ (e)    & cm    & n a  \\ \hline
Life Science &  -  & $10^{15}$  & 1     & 100-1000 &1-4  &1 to 5  &     &mm    & n a  \\ \hline
$\mu$CF          &  -  & $10^{19}$  & 1     &$\geq 1000$ & $\geq 100$  &      &     &    &  n a.  \\ 
\br
\end{tabular}
%\end{indented}
\end{table}








 It is clear that although fluxes are an important 
ingredient , the time structure of the beam is often a key parameter to 
optimize the
conditions of the experiments. Those requirements should be considered  in
 the design of the neutrino factory front end and its proton driver accelerator
 as it could
had considerable attraction to users of such muon sources.

\newpage

\section{REFERENCES: }

\begin{thebibliography}{20} 
  

\bibitem{n1}{J.Aysto et al.,{\it hep-ph/0109217} {CERN-TH/2001-231}} \\

\bibitem{n2}{Y. Kuno and Y. Okada, {\it Rev. Mod. Phys.} {\bf 73} (2001) 151} \\

\bibitem{n3} {J.Hisano and D.Nomura, {\it Phys. Rev. }{\bf D59} 116005} \\

\bibitem{n4} {G. Signorelli, } {\it these proceedings} \\

\bibitem{n5} {M. Aoki, } { \it these proceedings} \\

\bibitem{n51} {Y.Kuno  } { \it Proceedings of the  High Intensity secondary beam with Phase Rotation Workshop,}{Kyoto University(Sept 1998)} \\

\bibitem{n6} {D. Tomono, }{ \it these proceedings} \\

\bibitem{n3.1} {W.Fetscher, }{ \it these proceedings} \\

\bibitem{n7}{L. Malgeri, } { \it these proceedings} \\

\bibitem{n8}{K.S. Babu and Sandip Pakvasa, }{ \it hep-ph/0204236}(2002) \\

\bibitem{n9}{K.Nagamine ,}{\it these proceedings} \\

\bibitem{n10.1}{K.Ishida, }{\it these proceedings} \\

\bibitem{n10}{P.Strasser, }{ \it Eur.Phys.J. {\bf A}}{\bf13}, 197-202 (2002) \\

\bibitem{n11}{E.Morenzoni, }{\it International workshop on future of muon science, }{ KEK Proceedings 2002-2, (May 2002) 8 } \\

\bibitem{n12}{DAI-Omega project, }{\it International workshop on future of muon science, }{ KEK Proceedings 2002-2 (2002) 58-59 } \\

\end{thebibliography}

\end{document}

 
 
