Physical Review D 78,3 ( 2008 )
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(1S)->gamma gg, via the "tagged" process: e(+)e(-)->psi(2S); psi(2S)-> J/psi pi(+)pi(-); J/psi ->gamma+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 [R-gamma=B(gg gamma)/B(ggg)] to be R-gamma=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 -> gg gamma. The R-gamma value obtained is roughly consistent with that expected by a simple quark-charge scaling [R-gamma similar to(q(c)/q(b))(2)] of the value determined at the Upsilon(1S), but somewhat higher than the value expected from the running of the strong coupling constant.
Astronomy & Astrophysics;; Physics, Particles & Fields
Date of this Version