Radiative muon absorption in calcium

The photon spectrum from radiative absorption of negative muons in ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ has been measured with a high-resolution pair spectrometer. The data are analyzed in order to determine the induced pseudoscalar coupling constant $g_p$ in nuclear matter. When compared to models which use a realistic nuclear response function and avoid the closure approximation, a value of $g_p$/$g_A$=4.0±1.5 is obtained, which indicates a quenching of this coupling compared to the nucleonic value by a factor 0.57±0.25.