Using 24 million $\psi' \equiv \psi(2S)$ decays in CLEO-c, we have searched for higher multipole admixtures in electric-dipole-dominated radiative transitions in charmonia. We find good agreement between our data and theoretical predictions for magnetic quadrupole (M2) amplitudes in the transitions $\psi' \to \gamma \chi_{ c1,2}$ and $\chi_{ c1,2} \to \gamma J/\psi$, in striking contrast to some previous measurements. Let $b_2^J$ and $a_2^J$ denote the normalized M2 amplitudes in the respective aforementioned decays, where the superscript $J$ refers to the angular momentum of the $\chi_{ cJ}$. By performing unbinned maximum likelihood fits to full five-parameter angular distributions, we determine the ratios $a_2^{ J=1}/a_2^{ J=2} = 0.67^{ +0.19}_{ -0.13}$ and $a_2^{ J=1}/b_2^{ J=1} = -2.27^{ +0.57}_{ -0.99}$, where the theoretical predictions are independent of the charmed quark magnetic moment and are $a_2^{ J=1}/a_2^{ J=2} = 0.676 \pm 0.071$ and $a_2^{ J=1}/b_2^{ J=1} = -2.27 \pm 0.16$.
Categories: hep-ex