First measurement of form factors of the decay Ξ0→Σ+ e-(ν)over-bare -: art. no. 132001

We present the first measurement of the form factor ratios g(1)/f(1) (direct axial vector to vector), g(2)/f(1) (second class current), and f(2)/f(1) (weak magnetism) for the decay Xi (o) --> Sigma (+)e(-)<()over bar>(e) using the KTeV (E799) beam line and detector at Fermilab. From the Sigma (+) polarization measured with the decay Sigma (+) --> p pi (o) and the e(-) - <()over bar> correlation, we measure g(1)/f(1) to be 1.32 (+0.21)(-0.17) (stat) +/- 0.05(syst), assuming the SU(3)(f) (flavor) values for g(2)/f(1) and f(2)/f(1). Our results are all consistent with exact SU(3)(f) symmetry.