Search

A precision measurement of the 277 keV γ ray produced by capturing muons in gaseous oxygen was performed using high-resolution HPGe detectors. The Doppler-broadened shape of this line is sensitive to the possible admixture into muon capture of genuine scalar interaction. This experiment complements, in the muon sector, in principle, similar ones undertaken recently in nuclear β decay. Using a procedure discussed in earlier papers, a fit to the experimental line-shape allowed us to obtain for the recoil–gamma correlation coefficient the value of a 1 2 =0.096±0.041 (95% CL). The available evaluations of the contributing nuclear matrix elements, performed in the impulse approximation in the absence of scalar interaction, produce correlation coefficients in disagreement with our result. These evaluations are independent of the induced pseudoscalar coupling and so of the validity of the PCAC hypothesis, but their reliability and model dependence remain to be investigated.

The NEMO-2 tracking detector located in the Frejus Underground Laboratory was designed as a prototype for the NEMO-3 detector and to study different modes of double beta decay. Measurements with 100 Mo, 116 Cd, 82 Se and 96 Zr were carried out. Presented here are the experimental half-life limits on double beta decays for new Majoron emission modes and limits on effective neutrino–Majoron coupling constants.

We describe an improved follow-up of our previous spin-neutrino correlation experiment, where the 1229 and 2171 keV gamma-rays emitted after the 28 Si( μ , ν ) 28 Al(1 + , 2202 keV) reaction were observed by high-resolution HPGe detectors at different angles with respect to the muon spin. In the experiment described here, a magnetic field was used both to select events according to the spin-gamma angle and to measure the residual muon polarization by the muSR method. We further increase the precision of our result making use of new experimental and theoretical information. We obtain for the parameter x ≡ M (2)/ M (−1) the value of x =0.239±0.029, which can be compared to our previous result (Brudanin et al., Nucl. Phys. A 587 (1995) 577) x =0.254±0.034 and to the value x =0.315±0.080 obtained recently at TRIUMF with a different technique. The coupling-constant ratio g P / g A was deduced from the mean value x =0.247±0.027. Using renormalized transition operators calculated recently, we obtained for g P / g A the solution range of −1.0 to +1.3 to be compared to the value of 7 predicted by PCAC for the free nucleon. This result confirms the strong quenching of g P / g A reported earlier.