Initialize a repository for writeup

AlCapPSI/PSI.tex

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+%[This is not official and for distribution, as we still have to discuss with TRIUMF management.]
+
+An initial test run for measuring protons emitted from Al targets was performed by a subset of this collaboration
+at PSI in 2009. It helped to commission part of the apparatus used for the current proposal. It also showed
+deficiencies which helped to define and optimize the set-up proposed here. In particular, the beam 
+quality, the X-ray detection, the thin dE/dx detectors, the shielding of stray muons etc. need additional
+careful attention.
+
+In 2012, a joint COMET/Mu2e project on  charged particle emission was started, when the high relevance of
+proton emission for the new COMET Phase-I idea was realized. Due to the geographical advantage of
+Vancouver, as a good crossing point for the Fermilab and J-PARC collaboration, a proposal~\cite{triumf12}
+ was submitted to  TRIUMF in summer 2012, and accepted with high priority. The PAC recommendation reads:\\
+{\it\bf ``The proposed set of muon capture background measurements are deemed crucial to the design and understanding of future neutrino-less muon-to-electron decay experiments, such as COMET and mu2e. Thus the committee approves this proposal with high scientific priority. 
+It is noted that it is not yet clear which muon beamline will be available for this study with the desired negative muon properties. 
+Once a suitable beamline has been identified that will be ready and available on the required timescales, the committee recommends that the full 36 shifts be granted.''}
+
+Unfortunately, the above-mentioned availability of a suitable beamline for low energy $\mu^-$ turned out to be a problem.
+The allocated test beam times in fall of 2012 could not be realized, as the M9B beamline experienced vacuum problems
+at the T2 target station as well as difficulties with the superconducting decay channel. Moreover, TRIUMF cloud beamlines
+with better momentum bin essential for this experiment, are not foreseen to be operated with negative muons.
+In this situation, the collaboration asked the TRIUMF management to put S1371 on standby.
+
+Meanwhile, PSI built a new low energy muon beam for particle physics, initially for the MuSun experiment. This
+beamline was successfully commissioned by the MuSun collaboration, including some members of the present
+collaboration. The results were extremely positive. In particular, the beamline appears to be the world-wide 
+superior channel for experiments needing muon beam \textit{at low energies with very narrow energy spread}.
+This advantage is due to the high proton intensity at PSI, combined with a special cloud muon channel,
+which selects the momentum with three bending magnets and thus allows for a dispersive focus.
+  The initial commissioning results by the MuSun collaboration promise excellent conditions for the thin
+targets anticipated in AlCap. Further beam details are discussed in the MuSun progress report, submitted to this BVR.
+