Study of the K+ π+ π- final state in B+ → J/ψ K+ π+ π- and B+ → ψ′ K+ π+ π-

Using 535 X 10(6) B-meson pairs collected by the Belle detector at the KEKB e(+)e(-) collider, we measure branching fractions of (7.16 +/- 0.10(stat) +/- 0.60(syst) X 10(-4) for B+ -> J/psi K+ pi(+) pi(-) and (4.31 +/- 0.20(stat) +/- 0.50(syst)) X 10(-4) for B+ -> psi' K+ pi(+) pi(-). We perform amplitude analyses to determine the resonant structure of the K+ pi(+) pi(-) final state in B+ -> J/psi K+ pi(+) pi(-) and B+ -> psi' K+ pi(+) pi(-) and find that the K-1(1270) is a prominent component of both decay modes. There is significant interference among the different intermediate states, which leads, in particular, to a striking distortion of the rho line shape due to the omega. Based on the results of the fit to the B+ -> J/psi K+ pi(+) pi(-) data, the relative decay fractions of the K-1(1270) to K rho, K omega, and K*(892)pi are consistent with previous measurements, but the decay fraction to K-0(*)(1430) is significantly smaller. Finally, by floating the mass and width of the K-1(1270) in an additional fit of the B+ -> J/psi K+ pi(+) pi(-) data, we measure a mass of (1248.1 +/- 3.3(stat) +/- 1.4(syst)) MeV/c(2) and a width of (119.5 +/- 5.2(stat) +/- 6.7(syst)) MeV/c(2) for the K-1(1270).