Muon beams

It is the interplay between particle physics and QED phenomena in the muonium atom which cause increasing understanding of fundamental forces and increasing reliability of extracted fundamental constants. None of both sides could reach significant results without the other. With the significant improvement expected for muon beam rates at various places we can look forward to further insights and maybe hints why there are particle generations. 

Of course, prior to any realization of a laser setup, the formation of polarized muonic hydrogen needs to be verified in a first experimental phase. Therefore a slow polarized muon beam would be required. These steps could start already at low intensity muon sources such as PSI or RAL where depending on the achievable polarization and fluxes also a first experiment (presumably with low... 

High-Intensity Low-Energy Muon Beam Line... 

Improvement by a factor of about 10 in the sensitivity of the comparison of theory and experiment for Av appears possible at this time.9 With the use of a chopped muon beam now available at Los Alamos, line narrowing techniques can be employed.10 Use of a higher magnetic field value will improve the accuracy in determining p /pp. Finally, the intensity and quality of the muon beam has been improved since the last measurement. Considering all these factors, a measurement of Av to about 5 ppb and of p /up to 30 ppb appears possible. 

Using the high intensity pulsed muon beam from the Rutherford Laboratory 1 GeV proton synchrotron, the Heidelberg group has initiated a new experiment... 

Table 3 gives the relevant figures for the muon beam (AGS operation normally 1 burst each 1.4 seconds). 

Muon beam parameters per burst (1012 protons on target)... 

See also J. French Thesis Nevis 263 (1987) R/1379, CU/369 and A. Blaer, J. French, M. May, A.M. Sachs and E. Zavattini Measurement of K X-rays from muonic helium formed in a low density target in an intense pulsed muon beam, to be published. 

Muonium (Mu) is the lightest hydrogen-like atom (mMu = 0.11 mH) available for chemical research it has a positive muon (/jl+, t = 2.2 fisec) as the nucleus. The muon spin resonance (/tSR) technique is described in several review articles (16, 99—102). Most of the research is performed in the condensed phases, but because of the development of the surface muon beams (103, 104), experiments in the gaseous phase have received more attention. At present three muonic fractions can be detected (1) fan, free muonium (2) fa, free n+, or Mu bound in a diamagnetic compound and (3) fa, Mu bound in a paramagnetic compound. In liquid phases, there is quite often a missing fraction, fa = 1 -fau - fa - fa ... 

The experiments described above were made on powder samples of 99.999% purity from Alfa Aesar. Single-crystal studies have also been undertaken. Figure 3 shows spectra of an Eagle-Picher sample taken at two different orientations of the crystallographic c-axis with respect to the muon beam the inset gives the orientation dependence of the separation of the main satellite lines. 

Table I lists the decay constants, X, obtained for the different concentrations of the monomers studied. These Xs are the average of the left and right values obtained for each concentration (11). Though statistical errors range from 5% to 17%, experimental irreproducibilities in target geometry, field homogeneity, detector thresholds, muon beam asymmetry and background result in a more probable error of 25% ( ). This level of reproducibility is quite reasonable when compared to rate constants obtained by competitive rate techniques and direct physical methods.

The 1S-2S transition in muonium has also been measured by laser spectroscopy. The transition is induced by a two-photon Doppler-free process and detected through the subsequent photoionization of the 2S state in the laser field. The key to success in this experiment was the production of muonium into vacuum from the surface of heated W or of Si02 powder. The discovery experiment(33) was done at the KEK facility in Japan with a pulsed muon beam and an intense pulsed laser system. A subsequent experiment(34) done with the pulsed beam at RAL and a similar pulsed laser has improved the signal substantially and has achieved a a precision of about lO" in the 1S- 2S interval, thus determining the Lamb shift in the IS state to about 1% accuracy (Fig. 22). The precision of this experiment should be greatly improved in a new experiment now underway at RAL. This experiment will provide a precise... 

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