Measurement of structure dependent K+ ---> muon+ neutrino(muon) gamma decay

The E787 collaboration Adler, S. ; Atiya, M.S. ; Chiang, I-H. ; et al.
Phys.Rev.Lett. 85 (2000) 2256-2259, 2000.
Inspire Record 525021 DOI 10.17182/hepdata.19424

We report the first measurement of a structure dependent component in the decay K^+ -> mu^+ nu gamma. Using the kinematic region where the muon kinetic energy is greater than 137 MeV and the photon energy is greater than 90 MeV, we find that the absolute value of the sum of the vector and axial-vector form factors is |F_V+F_A| =0.165 \pm 0.007 \pm 0.011. This corresponds to a branching ratio of BR(SD^+) = (1.33 \pm 0.12 \pm 0.18) \times 10^{-5}. We also set the limit -0.04 < F_V-F_A < 0.24 at 90% c.l.

1 data table

Q2 independence of the formfactors is assumed.