Search

A TRIUMF experiment, PIENU, which aims to measure the branching ratio of pion decays, R = Γ(π→eν+eνγ)/Γ(π→μν+μνγ) to a precision of 0.1% or better is described. Such a measurement provides the best test of electron-muon universality in weak interactions and is sensitive to an effective mass scale of up to 1000 TeV in new physics.

The branching ratio of pion decays, R = Γ(π+→e+νe+π+→e+νeγ)Γ(π+→μ+νμ+π+→μ+νμγ is one of the most accurately calculated decay processes involving hadrons and has provided one of the most stringent tests of the hypothesis of electron-muon universality in weak interactions. The current experimental branching ratio Rexp = (1.230±0.004)×10−4 is 40 times less precise than the theoretical prediction RSM = 1.2352(1)10−4. The TRIUMF PIENU experiment aims at measuring the pion branching ratio with a precision improved by at least a factor five.

Evidence of massive neutrinos in the π+→e+ν decay spectrum was sought with the background π+→μ+→e+ decay chain highly suppressed. Upper limits (90% C.L.) on the neutrino mixing matrix element |Uei|2 in the neutrino mass region 60-129 MeV/c2 were set at the level of 10−8.

A TRIUMF experiment, PIENU, which aims to measure the branching ratio of pion decays, R = Γ(π→eν+eνγ)/Γ(π→μν+μνγ) to a precision of 0.1% or better is described. Such a measurement provides the best test of electron‐muon universality in weak interactions and is sensitive to an effective mass scale of up to 1000 TeV in new physics.A TRIUMF experiment, PIENU, which aims to measure the branching ratio of pion decays, R = Γ(π→eν+eνγ)/Γ(π→μν+μνγ) to a precision of 0.1% or better is described. Such a measurement provides the best test of electron‐muon universality in weak interactions and is sensitive to an effective mass scale of up to 1000 TeV in new physics.

We report preliminary results of π photo‐production using polarized γ beams and a polarized HD target. Four observables can be extracted simultaneously from the data, the cross section, the beam asymmetry Σ, and the double‐polarization observables G and E. The latter determines the GDH sum rule integral.

Frozen‐spin HD polarized targets operating between 0.4 and 4K, used with cold‐transfer (4K) techniques, provide great configurational flexibility. Their long depolarization times under target usage conditions assure reasonable match between polarization production and usage times, for weakly ionizing beam fluxes, and the very long relaxation times at fields above 7T (∼1 yr.) provide an economical storage mode and ‘‘off‐the‐shelf’’ availability.

We report the observation of the elementary process {mu}{sup {minus}}{ital p}{r_arrow}{ital n}{nu}{sub {mu}}{gamma} at TRIUMF. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

A large acceptance, medium energy resolution, cylindrical drift chamber has been constructed for use as a pair spectrometer for the detection of 50 to 100 MeV photons from radiative muon capture. Energy resolution for the detection of 129 MeV photons was found to be 12% (FWHM) at a magnetic field of 2.4 kG and 5.5% at 7.1 kG with the resolution improving as the photon energy decreases. The worst case position resolution for particle tracks is 150 microns (σ). The acceptance for the detection of photons over the range 55–83 MeV was found to be 0.66% at 2.4 kG. All of these properties are reproduced by a Monte Carlo simulation of the spectrometer. Triggering schemes and further chamber characteristics will also be discussed.

The time projection chamber at TRIUMF is being used to search for muon‐electron conversion. The best spatial resolution in the TPC, σ≂200 μm, occurs at the minimum drift length and for an optimum track‐to‐anode crossing angle determined by the magnetic field. The observed resolution is dependent on th diffusion of the drifting electrons, the track‐to‐anode crossing angle, E↘×B↘ effects near the anode wire and the discrete nature of the ionization process. Distortions due to positive ions leaking back into the drift volume from the anode wire region have been nearly eliminated by the use of a pulsed dual grid system.

Limits on the lepton flavor violating reactions ..mu../sup -/+Z..-->..e/sup -/+Z and ..mu../sup -/+Z..-->..e/sup +/+(Z-2), muon-electron and muon-position conversion, have been obtained. Upper limits (90% C.L.) for the branching ratios compared to ordinary muon capture are: R/sub -/(Ti) = GAMMA(..mu../sup -/Ti..-->..e/sup -/Ti)/GAMMA(..mu../sup -/Ti capture) ..d/sup +/Ca*)/GAMMA(..mu../sup -/Ti capture)