Decay of negative muons bound in $^{27}$Al

Understand

We present the first measurement of the energy spectrum up to 70 MeV of electrons from the decay of negative muons after they become bound in $^{27}$Al atoms.

• The data were taken with the TWIST apparatus at TRIUMF.
• We find a muon lifetime of (864.6 $\pm$ 1.2) ns, in agreement with earlier measurements.
• The asymmetry of the decay spectrum is consistent with zero, indicating that the atomic capture has completely depolarised the muons.