Radiative muon capture on hydrogen

The radiative muon capture (RMC) rate on hydrogen is particularly sensitive to the induced pseudoscalar coupling strength gρ, of the weak hadronic current. Due to the very small branching ratio (∼10-8) for this reaction, it has not been observed until now. Photons with energies between 40 and 140 MeV are detected in a large acceptance pair spectrometer. Subtraction of backgrounds due to pion contamination in the muon beam, high energy tail events in the spectrometer response function, muon stops in the target walls, cosmic rays and random events, yields the final RMC photon spectrum between 56 and 110 MeV. A preliminary spectrum for RMC on hydrogen will be presented and the extracted value of gρ, will be compared to the Goldberger-Treiman prediction. (author)