Search

A search has been performed for the muon-number--violating decay ..mu -->..e/sup +/e/sup +/e/sup -/. No candidate event has been found, the result yielding an upper limit for the branching ratio of B/sub mu3e/ ..e/sup +/e/sup +/e/sup -/..nu../sub e/nu-bar/sub ..mu../ events, eleven such events were observed. They agree in number and spectra with expectations based on standard electroweak theory.

A search with the Crystal Box detector shows no evidence for the lepton-family-number-nonconserving decays ..mu -->..e..gamma.., ..mu -->..e..gamma gamma.., or ..mu -->..eee. The search provides upper limits for the branching ratios of GAMMA(..mu -->..e..gamma..)/GAMMA(..mu -->..evv-italic-bar) ..e..gamma gamma..)/GAMMA(..mu -->..evv-italic-bar) ..eee)/GAMMA(..mu -->..evv-italic-bar)

A search has been performed for the decays μ → eee, μ → e γ , and μ → eγγ with a sensitivity in the branching ratios at the level of 10 −10 . The experiment used a separated, 26 MeV/c μ + beam with an average intensity of 300kHz. A total of 2.2 × 10 11 muon decays were examined for the present result. The detector for the experiment Is the Crystal Box, which consists of a cylindrical drift chamber surrounded by 396 NaI(T1) crystals. A layer of scintillation counters in front of the crystals provided timing for electrons and a veto for photons. The energy resolution for electrons and photons is ≈6% (FWHM). The position resolution of the drift chamber is 350 μm leading to a vertex cut with a rejection of 10 3 for μ → eee. The timing resolution is ≈300 ps from the scintillators and ~1 ns from the crystals. No candidate for μ → eee has been found, yielding an upper limit for the branching ratio of B μ 3e −10 (90% C.L.).

An array of 49 NaI(Tl) modules each 20 inch in depth and 2.5 inch × 2.5 inch in cross section has been constructed and its properties, especially energy resolution, explored for positrons in the range 20 MeV – 18 GeV. A subsequent much larger detector, the Crystal Box, has also been constructed from 396 modules of the same cross section, but mostly 12 inch in depth, and operated as a γ-ray and positron detector in a search for rare muon decays. The calibration procedure used for the Crystal Box and its characteristic resolutions in energy, impact point and time are described.

A very low momentum, high purity positive muon beam has been developed at LAMPF, utilizing muons which originate from pion decays at rest in the target for the primary proton beam and are transported by the LAMPF stopped muon channel. The channel is tuned to transport muons with momenta as low as 3 MeV/c and hence selects muons originating some distance below the target surface (subsurface muons). A static E × B separator largely eliminates the e+ component in the beam.

This Letter reports a new experimental search for the family-number-nonconserving decay ..mu../sup +/ ..-->.. e/sup +/..gamma... There is no evidence for the presence of this decay mode. The upper limit for the branching ratio is GAMMA(..mu.. ..-->.. e..gamma..)/GAMMA(..mu.. ..-->.. enu anti nu) < 4.9 x 10/sup -11/ (90% C.L.). 13 refs., 3 figs.

A new experimental search with the Crystal Box detector shows no evidence for the lepton-family-number--nonconserving decay ..mu../sup +/..-->..e/sup +/..gamma gamma... This corresponds to an upper limit for the branching ratio of GAMMA(..mu -->..e..gamma gamma..)/GAMMA(..mu -->..e..nu..nu-bar)

Muon rates and polarizations have been measured on several beam channels at LAMPF to characterize muon production from the primary target surface or adjacent volume. To produce these "surface" or "cloud" beams, the channel is tuned to accept beam directly from the target. The measurements range from 20-200 MeV/c in muon momentum at production angles of 20, 45, and 65°. Both ?+ and ?- rates, and ?+ polarization were measured. Surface beam polarization is close to 100%, while cloud beam polarization is low. The surface ?+ rate dependence upon proton beam depth in the target was studied.

New experimental upper limits for the branching ratios of the lepton‐family‐number nonconserving decays μ+ → e+γ and μ+ → e+γγ are presented. A new determination of γ, the ratio of pion axial‐vector to vector form factors, from radiative pion decay is also reported. These results are from data taken with the Crystal Box detector at LAMPF.

A search has been performed for the decays μ → eee, μ → eγ, and μ → eγγ with a sensitivity in the branching ratios at the level of 10−10. The experiment used a surface muon beam at LAMPF with an average intensity of 300 kHz. A total of ≳1011 muon decays was examined for the present result. The detector for the experiment is the Crystal Box which consists of a cylindrical drift chamber surrounded by 396 NaI(T1) crystals. A layer of scintillation counters in front of the crystals provided timing for electrons and a veto for photons. The energy resolution for electrons and photons is ∼6% (FWHM). The position resolution of the drift chamber is 350 μm leading to a vertex cut with a rejection of 103 for μ → eee. The timing resolution is ∼400 ps from the scintillators and ∼1 ns from the crystals. From these values, the eee and eγγ limits are expected to be background free.

Development of the Crystal Box Spectrometer at the Clinton P. Anderson Meson Physics Facility in Los Alamos has been completed. And a search for the rare muon decays mu to e−gamma, to e−2gamma, and to 3e is ready to start taking data. (AIP)