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 $2\mathrm{\hslash }\omega$ wavefunction admixtures.