The spin-neutrino correlation revisited in Si-28 muon capture: a new determination of the induced pseudoscalar coupling g(p)/g(A)

We describe an improved follow-up of our previous spin-neutrino correlation experiment, where the 1229 and 2171 keV gamma-rays emitted after the Si-28 (mu,v)Al-28(1(+), 2202 keV) reaction were observed by high-resolution HPGe detectors at different angles with respect to the muon spin. In the experim ent described here, a magnetic field was used both to select events accordi ng 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 experimen tal 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 re sult (Brudanin et al., Nucl. Phys. A 587 (1995) 577) x = 0.254 +/- 0.034 an d to the value x = 0.315 +/- 0.080 obtained recently at TRIUMF with a diffe rent technique. The coupling-constant ratio g(P)/g(A) was deduced from the mean value x = 0.247 +/- 0.027. Using renormalized transition operators cal culated 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 nucleo n. This result confirms the strong quenching of g(P)/g(A) reported earlier. (C) 2000 Elsevier Science B.V. All rights reserved.