Dispersive analysis with ρ-ω mixing produces a two-parameter fit describing BESIII data on the J/ψ→π⁰γ* form factor from 0 to 2.8 GeV and extracts a (62 ± 21)° relative phase between strong and electromagnetic modes.
Inclusive Radiative $J/\psi$ Decays
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abstract
Using data taken with the CLEO-c detector at the Cornell Electron Storage Ring, we have investigated the direct photon momentum spectrum in the decay J/psi->gamma+gluon+gluon, via the 'tagged' process: e+e- -> psi(2S); psi(2S)->J/psi pi+pi-; J/psi->photon + X. Including contributions from two-body radiative decay processes, we find the ratio of the inclusive direct photon branching fraction to that of the dominant three-gluon branching fraction to be R=0.137+/-0.001+/-0.016+/-0.004, where the errors shown are statistical, systematic, and the model-dependent uncertainty related to the extrapolation to zero photon energy. The shape of the scaled photon energy spectrum in J/psi->gg gamma is observed to be very similar to that of Upsilon(1S)->gg gamma. The R value obtained is roughly consistent with that expected by a simple quark-charge scaling of the value determined at the Upsilon(1S), but somewhat higher than the value expected from the running of the strong coupling constant.
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Dispersive analysis of the $J/\psi\to\pi^0 \gamma^\ast$ transition form factor with $\rho$-$\omega$ mixing effects
Dispersive analysis with ρ-ω mixing produces a two-parameter fit describing BESIII data on the J/ψ→π⁰γ* form factor from 0 to 2.8 GeV and extracts a (62 ± 21)° relative phase between strong and electromagnetic modes.