Muon capture in ²⁸Si

A measurement has been made of the angular correlation of the neutrino with a specific nuclear de-excitation γ-ray following exclusive muon capture on ²⁸Si , in order to determine the size of the induced-pseudoscalar coupling constant gp of the weak hadronic current. The correlation is observed via the Doppler-broadened line shape of the 1229 keV ²⁸ Al γ-ray, which is measured using a pair of Comptonsuppressed intrinsic Ge detectors. Significant background suppression is achieved through the use of a coincidence technique in which the 1229 keV γ-ray of interest is 'tagged' by the subsequent 942 keV γ-ray in the cascade, which is detected in an array of 24 NaI(Tl) scintillators. Through a detailed attention to the detectors' response functions as well as the use of background-subtracted spectra, the γ — v correlation coefficient a is found to be 0.360±0.059 i n good agreement with a recent measurement at Dubna. The result obtained yields the value of gp/gA = 0.0±3.2 when compared to the latest calculation of the γ — v angular correlation, suggesting a massive quenching of the induced-pseudoscalar coupling constant in 2 8 S i in comparison with the value expected for a free nucleon. However other available calculations give the values gp/gA — 5.3±2.0 and gp/gA = 4.2±2.5, but the model-dependence of these intriguing results has yet to be assessed fully. A measurement of the correlation coefficient a of the 2171 keV ( 1⁺ → 2⁺) γ-ray has solved the enigma of the unphysical result that was found by a previous experiment. In addition, the lifetime of the 2201 keV ²⁸ Al level has been measuredScience, Faculty ofPhysics and Astronomy, Department ofGraduat

A study of X and gamma rays following muon capture in 28Si

Negative muons produced via the backward decay of pions in the M9b beam channel at TRIUMF were stopped in a ²⁸Si target. The energies of the muonic X-rays and nuclear γ-rays following the muon capture were measured in order to identify a Doppler broadened γ ray line in ²⁸A1 which is suitable for analysis in terms of a γ — ν angular correlation to determine a value for the induced-pseudoscalar coupling constant (gp ). The muon beam was also stopped in 6 other background targets ( polythene, A1, stainless steel, Cu, Pb and BGO ) and their X- and γ-ray energies have been studied so as to fully understand the backgrounds associated with such a transition.Science, Faculty ofPhysics and Astronomy, Department ofGraduat