Abstract
We study the decays of the J/ψ and ψ′ mesons to π+π−π0 using data samples at both resonances collected with the BES III detector in 2009. We measure the corresponding branching fractions with unprecedented precision and provide mass spectra and Dalitz plots. The branching fraction for J/ψ→π+π−π0 is determined to be(2.137±0.004 (stat.)−0.056+0.058 (syst.)−0.026+0.027 (norm.))×10−2, and the branching fraction for ψ′→π+π−π0 is measured as(2.14±0.03 (stat.)−0.07+0.08 (syst.)−0.08+0.09 (norm.))×10−4. The J/ψ decay is found to be dominated by an intermediate ρ(770) state, whereas the ψ′ decay is dominated by di-pion masses around 2.2 GeV/c2, leading to strikingly different Dalitz distributions.
Highlights
IntroductionIn this Letter we present new measurements of the J /ψ −→ π +π −π 0 and ψ −→ π +π −π 0 branching fractions with unprecedented precision using the large data samples collected with the BES III detector at the J /ψ and ψ resonances
Previous studies of J /ψ −→ π +π −π 0 [1,2,3,4] and ψ −→ π +π −π 0 [1,5,6] found an unexpectedly low branching fraction in the case of the ψ 6 (world averages: BF( J /ψ −→ π +π −π 0) = (2.07 ± 0.12) × 10−2 and BF(ψ −→ π +π −π 0) = (1.68 ± 0.26) × 10−4 [8]) and a completely different shape of the di-pion mass spectrum and the Dalitz plot
In this Letter we present new measurements of the J /ψ −→ π +π −π 0 and ψ −→ π +π −π 0 branching fractions with unprecedented precision using the large data samples collected with the BES III detector at the J /ψ and ψ resonances
Summary
In this Letter we present new measurements of the J /ψ −→ π +π −π 0 and ψ −→ π +π −π 0 branching fractions with unprecedented precision using the large data samples collected with the BES III detector at the J /ψ and ψ resonances. These measurements are an important first step to an experimental inquiry into the puzzle of the decay dynamics, preparing the way for a detailed analysis. The large branching fraction of J /ψ −→ π +π −π 0 makes it an important background process for many other studies (e.g. the scalar meson spectrum in J /ψ −→ γ π +π −), an improved knowledge of this branching fraction will enhance the precision of those measurements
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