Study of e+e- => B(*) B(*)-bar pi+- at sqrt(s)=10.866 GeV

We report the analysis of the three-body e+e- => B B-bar pi, B B*-bar pi, and B* B*-bar pi processes, including the first observation of the Zb±(10610) =>[B B*-bar+c.c.]± and Zb±(10650) => [BB-bar]± transitions. We measure visible cross sections for the three-body production of sigma_vis(e+e- => [B B*-bar+c.c.]±pi-+=(11.2±1.0(stat.)±1.2(syst.)) pb and sigma_vis(e+e- => [BB-bar]±pi-+)=(5.61±0.73(stat.)±0.66(syst.)) pb and set a 90% C.L. upper limit of sigma_vis(e+e- => [BB-bar]±pi-+)<2.1 pb. The results are based on a 121.4 1/fb data sample collected with the Belle detector at a center-of-mass energy near the Y(5S) peak.