Study of the K+ pi+ pi- Final State in B+ -> J/psi K+ pi+ pi- and B+ -> psi-prime K+ pi+ pi-

TL;DR

This study measures branching fractions and analyzes the resonant structure of the K+ pi+ pi- final state in B+ decays to J/psi and psi-prime, revealing dominant K_1(1270) contributions and interference effects.

Contribution

It provides precise measurements of branching fractions and detailed amplitude analyses, including the first measurement of the K_1(1270) mass and width in these decay modes.

Findings

Branching fraction for B+ -> J/psi K+ pi+ pi- is (7.16 +/- 0.10(stat) +/- 0.60(syst)) x 10^-4.

Branching fraction for B+ -> psi-prime K+ pi+ pi- is (4.31 +/- 0.20(stat) +/- 0.50(syst)) x 10^-4.

K_1(1270) is a prominent component with measured mass (1248.1 +/- 3.3(stat) +/- 1.4(syst)) MeV/c^2 and width (119.5 +/- 5.2(stat) +/- 6.7(syst)) MeV/c^2.

Abstract

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-prime 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-prime 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).