Partial wave analyses of J/psi to gamma pi^+ pi^- and gamma pi^0 pi^0

TL;DR

This study performs partial wave analyses of J/psi radiative decays to pi pi pairs, identifying scalar meson states and their properties, using a large dataset and relativistic tensor amplitude methods.

Contribution

It reports the observation and characterization of two scalar meson states in J/psi decays, including their masses, widths, and branching ratios, with a novel analysis approach.

Findings

Identification of a 0++ state at 1466 MeV/c^2 with specific mass and width.

Observation of a second 0++ state at 1765 MeV/c^2 with detailed properties.

Determination that spin 0 is strongly favored over spin 2 for the observed states.

Abstract

Results are presented on J/psi radiative decays to pi^+pi^- and pi^0pi^0 based on a sample of 58M J/psi events taken with the BESII detector. Partial wave analyses are carried out using the relativistic covariant tensor amplitude method in the 1.0 to 2.3 GeV/c^2 pipi mass range. There are conspicuous peaks due to the f_2(1270) and two 0^++ states in the 1.45 and 1.75 GeV/c^2 mass regions. The first 0^++ state has a mass of 1466\pm 6\pm 20 MeV/c^2, a width of 108^{+14}_{-11}\pm 25 MeV/c^2, and a branching fraction B(J/psi \to \gamma f_0(1500) \to\gamma \pi^+\pi^-) = (0.67\pm0.02\pm0.30) \times 10^{-4}. Spin 0 is strongly preferred over spin 2. The second 0^++ state peaks at 1765^{+4}_{-3}\pm 13 MeV/c^2 with a width of 145\pm8\pm69 MeV/c^2. If this 0^++ is interpreted as coming from f_0(1710), the ratio of its branching fractions to pipi and K\bar K is 0.41^{+0.11}_{-0.17}.