D. H. Wright

Radiative Muon Capture on Hydrogen and the Induced Pseudoscalar Coupling

Next to the hydrogen atom, the µ − p system is the most fundamental lepton-hadron system; therefore it can be used to test and extend our basic knowledge of the weak semi-leptonic interaction between leptons and quarks. Radiative muon capture (RMC) is much more sensitive than ordinary muon capture (OMC) to the induced pseudoscalar coupling constant of the weak semi-leptonic current because of the much larger range of momentum transfers which can occur in RMC. A status report on TRIUMF E452, Radiative Muon Capture on Hydrogen, which is anticipating a 10% measurement of this coupling constant, is presented.

Apparatus for a search for T-violating muon polarization in stopped-kaon decays

Abstract The detector built at KEK to search for T-violating transverse muon polarization in K + → π 0 μ + ν μ ( K μ 3 ) decay of stopped kaons is described. Sensitivity to the transverse polarization component is obtained from reconstruction of the decay plane by tracking the μ+ through a toroidal spectrometer and detecting the π0 in a segmented CsI(Tl) photon calorimeter. The muon polarization was obtained from the decay positron asymmetry of muons stopped in a polarimeter. The detector included features which minimized systematic errors while maintaining high acceptance.

Ortho-Para Transition Rate in mu-Molecular Hydrogen and the Proton's Induced Pseudoscalar Coupling g~p

We report a measurement of the ortho-para transition rate in the p mu p molecule. The experiment was conducted at TRIUMF via the measurement of the time dependence of the 5.2 MeV neutrons from muon capture in liquid hydrogen. The measurement yielded an ortho-para rate Lambda op = (11.1 +/- 1.7 +/-(0.9)(0.6)) x 10(4) s(-1), which is substantially larger than the earlier result of Bardin et al. The result has striking implications for the protons induced pseudoscalar coupling g(p), changing the value of g(p) obtained from the most precise ordinary muon capture measurement from 10.6 +/- 2.7 to 0.8 +/- 2.8, and from the sole radiative muon capture measurement from 12.2 +/- 1.1 to 10.6 +/- 1.2, bringing the latter result closer to theoretical predictions.

Measurement of hyperfine transition rates in muonic 19F, 23Na, 31P, and natCl

Abstract From the time dependence of the ( μ − , nν ) reaction we have determined the hyperfine transition rates for the muonic atoms of 19 F, 23 Na, and nat Cl, obtaining Λ h =4.9±1.2 μ s −1 , 8.4±1.9 μ s −1 , and 6.5±0.9 μ s −1 , respectively. Further, from the branching ratios of the ( μ −1 , ν ) reaction on muonic 31 P we have inferred a hyperfine transition rate that is much faster than the muon disappearance rate, Λ h ⪢ Λ D . These results are in reasonable agreement with the rates calculated for Auger emission, and qualitatively confirm the correction to the muonic atoms hyperfine splitting due to the distribution of magnetism in the nucleus. The 31 P result, however, disagrees with an earlier suggestion of the inhibition of Auger emission.

TWIST- The TRIUMF weak interaction symmetry test the Michel parameters from μ+ decay

Abstract We propose to make the first high precision measurements of nearly the entire differential spectrum (in energy and angle) of positrons from the decay of polarized muons. The main goal of the experiment is the precise testing of the ( V - A ) structure of electroweak interactions in the framework of the SU (2) L × U (1) model. Highly polarized “surface” μ + from the TRIUMF M13 beamline will enter a large volume, high field superconducting magnet on axis and will stop in a thin target at its center. The e + from the muon decay will be precisely tracked in the magnetic field using small-cell planar drift chambers. This spectrometer has been simulated with GEANT and EGS4 and has been demonstrated to meet the precision requirements.

Energy dependence of low-energy pion double-charge-exchange on the calcium isotopes

Abstract The forward angle differential cross sections of ( π + , π − ) reactions on the calcium isotopes to the double-isobaric-analog (DIAS) and ground states (GS) were measured between 25 and 65 MeV. These low-energy cross sections are up to an order of magnitude larger than those at resonance energies. The forward-angle excitation functions of 42 Ca, 44 Ca DIAS and 44 Ca GS transitions peak around 50 MeV. The 48 Ca DIAS cross section exhibits a minimum at about 50 MeV and that for the GS has a peak which is shifted to lower energy with a smaller cross section than that of the other nuclei. The observed behaviour is inconsistent with theoretical expectations.

The TRIUMF radiative muon capture facility

Abstract Radiative muon capture (RMC) on hydrogen produces photons with a yield of ∼10−8 per stopped muon. To measure RMC at TRIUMF we have constructed a large-solid-angle photon pair-spectrometer which surrounds the liquid hydrogen target. The spectrometer consists of a cylindrical photon converter and a large-volume cylindrical drift chamber to track the e+e− pairs. It is enclosed in a spectrometer magnet which produces a highly uniform axial magnetic field. The detector subsystems, the hardware trigger and the data acquisition system are described, chamber calibration and tracking techniques are presented, and the spectrometer performance and its Monte Carlo simulation are discussed.

Drift chambers for a precision measurement of the Michel parameters in muon decay

Planar drift chambers will be used in a solenoidal magnetic field to measure the Michel parameters in muon decay. The chamber manufacture procedure uses flat glass tables and precise ceramic glass spacers to provide precise anode– cathode spacing. Results of bench and beam tests of the prototype chambers are discussed. # 2001 Elsevier Science B.V. All rights reserved.

Search for exotic baryons in double radiative capture on pionic hydrogen

We report a search for low-lying exotic baryons via double radiative capture on pionic hydrogen. The data were collected at the TRIUMF cyclotron using the RMC spectrometer by detecting gamma-ray pairs from pion stops in liquid hydrogen. No evidence was found to support an earlier claim for exotic baryons of masses 1004 and 1044 MeV/

Radiative Muon Capture on 3He

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