Recoil alignment in muon capture on nitrogen-14
We report a measurement of the longitudinal alignment $A_L$ of the recoil nucleus in the $\mu^- + ^{14}$N$(1^+, 0)$ $\to$ $\nu_{\mu} + ^{14}$C$(2^+, 7012)$ transition. The experiment was performed on the M9B beamline at the TRIUMF cyclotron via the measurement of the Doppler lineshape of the subsequent $^{14}$C$(2^+, 7012)$ $\to$ $^{14}$C$(0^+, 0)$ gamma-rays. We compare our result $A_L = 0.60 \pm 0.11$ to various model calculations, and discuss the sensitivity to the induced pseudoscalar coupling, second-forbidden effects and $2 \hbar \omega$ wavefunction admixtures.