Inclusive Radiative psi(2S) Decays

Understand

Using e+e- collision data taken with the CLEO-c detector at the Cornell Electron Storage Ring, we have investigated the direct photon spectrum in the decay psi(2S)->gamma+gluon+gluon.

• We determine the ratio R of that inclusive direct photon decay rate to that of the three-gluon decay rate psi(2S)->3-gluon to be R(z>0.4)=0.070+/-0.002+/-0.019+/-0.011, with z defined as the scaled photon energy relative to the beam energy.
• The errors shown are statistical, systematic, and that due to the uncertainty in the input branching fractions used to extract the ratio, respectively.
• This R value is approximately 2/3 of the comparable value for the J/psi(1S), both in the region z>0.4, and also when extrapolated to the full range z>0.