First Observation of the Decay. Pi. . --]. Ee−e+. Nu. and a Determination of the Form Factors F

Download or read book First Observation of the Decay. Pi. . --]. Ee−e+. Nu. and a Determination of the Form Factors F written by and published by . This book was released on 1986 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The radiative pion decay .pi. .-->. ee−e+.nu. has been observed for the first time with a branching ratio of (3.4 +- 0.5) x 10−9. From the kinematical distribution of 79 events information on the form factors was extracted. The vector form factor F/sub V/ was found to have the same sign as the pion decay constant f/sub .pi./. For the axial-vector form factors the following values have been measured: .gamma. = F/sub A//F/sub V/ = 0.7 +- 0.5 and xi = R/F/sub V/ = 2.3 +- 0.6. This value of .gamma. agrees well with the small positive value of (0.53 +- 0.06) and excludes the large negative value obtained in .pi.+ .-->. e+.nu gamma. experiments. 8 refs. 8 refs.