The TWIST Experiment

The experiment was assembled at the TRIUMF cyclotron facility in Vancouver, BC. The "M13" beamline is used to produce a beam of muons with a well-defined spin orientation. The beamline is shown at left, with the TWIST magnet and detector shown at the right-hand side of the figure.

The measurements employ a large bore superconducting solenoid magnet (surplus from a Magnetic Resonance Imaging (MRI) company). Polarized positively charged muons produced at TRIUMF are directed into the magnetic field where they are stopped at the centre of a precision detector package. The magnet and the detectors are shown in concept form at the top of the TWIST home page. Photos of the magnet, and a "stack" of detectors - ready for insertation into the magnet - are shown below.

After an individual muon is stopped in the target, the tracking system is watched for several microseconds. If a muon decay event is observed, the positron from the decay spirals outward in the magnetic field. By observing the angle through which the positron is emitted and measuring the radius of curvature of the track in the magnetic field using precision tracking chambers, the angular and momentum distributions of decay events can be reconstructed. Sample decay spirals for one such decay are shown below.

By carefully controlling systematic uncertainties in the experiment, and by collecting data from a sample of 1,000,000,000 decay events, the decay distributions can be studied at an accuracy of parts in 10,000. This accuracy heightens our sensitivity to various effects, including the possible existence of right-handed interactions.

Return to the TWIST home page.