C. Q. Chen

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.

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.

Radiative muon capture on the proton

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 cylindrical pair spectrometer for the detection of medium energy photons

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.

Radiative muon capture on hydrogen

Symmetries are also very important to the physicist because they are each the result of an underlying conservation law. After many years of observation physicists have now come up with a Standard Model (SM) to describe both the elementary particles and the fundamental forces in nature. Within this Standard Model, the elementary particles consist of six leptons and six quarks which form three families each comprising one lepton pair and one quark pair. These elementary particles interact via only two forces: the strong force which is felt only by the quarks and the electroweak force which is felt by all particles. (The gravitational force has yet to be incorporated into the Standard Model.) The Standard Model has been amazingly successful in its description of the electroweak force. However, our basic model of the strong interaction, Quantum ChromoDynamics (QCD) is somewhat more complicated and our knowledge about the origins of the quark masses as well as the masses of the proton and neutron is still rather limited. Encoded in QCD are various symmetries which yield conserved currents that constrain both the fundamental interactions of the quarks and gluons and the resulting interactions of the nucleons and mesons. Thus, despite the complicated quark-gluon substructure of the nucleons, it is possible to make some precise predictions about their elementary properties.