Measurement of the induced pseudoscalar coupling constant from the rate of radiative muon capture on hydrogen

Radiative muon capture (RMC) on a proton is particularly sensitive to the induced pseudoscalar coupling strength gp, of the weak hadronic current. Hence a measurement of the rate of the RMC reaction in hydrogen is ideal for a precise determination of the value of gp. Until recently, such a measurement was not possible because of the very small branching ratio (∼10-8) of this reaction. 3.12 x 1012 μ- from the stopped muon channel at TRIUMF have been stopped in a very pure liquid 1H target (∼ 2 ppm 2H impurity). The resulting photons are detected in a 3π cylindrical drift chamber constructed for use as a pair spectrometer. After the subtraction of background photons due to bremsstrahlung, muon stops in the target walls and cosmic rays, about 250 photons remain in the RMC signal region of 58-100 MeV. Preliminary photon energy spectra will be presented and the extracted value of gp will be compared to the PCAC prediction