THE EXPERIMENTAL-STUDY OF THE PI(-)-]E-VBARGAMMA-DECAY IN FLIGHT

An experiment studying the radiative pion decay, π- → e-vγ, has been performed with a secondary 17 GeV negative pion beam on the IHEP machine with the ISTRA facility of the Institute for Nuclear Research. The high energy beam has enabled us to investigate this decay in a wide range of kinematic variables: Eγ > 21 MeV, Ee > 70-0.8Eγ MeV, which included events with θeγ > 60°. The axial-to-vector form factor ratio has been determined unambiguously: γ=0.41±0.023. The vector form factor has been determined in a model independent way: |Fv|=0.014±0.009. The probability of the π- → e-v γ decay was found to be BR = (1.61±0.23) × 10-7 for the region under consideration. The contributions of the inner bremsstrahlung and of the structure dependent radiation were investigated. A possible interpretation is discussed. © 1990.