Higher-order multipole amplitudes in charmonium radiative transitions
نویسندگان
چکیده
Using 24 million ψ′ ≡ ψ(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 ψ′ → γχc1,c2 and χc1,c2 → γJ/ψ, in striking contrast to some previous measurements. Let b2 and a2 denote the normalized M2 amplitudes in the respective aforementioned decays, where the superscript J refers to the angular momentum of the χcJ . By performing unbinned maximum likelihood fits to full five-parameter angular distributions, we found the following values of M2 admixtures for Jχ=1: aJ=1 2 = (−6.26± 0.63± 0.24)× 10−2 and bJ=1 2 = (2.76± 0.73± 0.23)× 10−2, which agree well with theoretical expectations for a vanishing anomalous magnetic moment of the charm quark. For Jχ=2, if we fix the electric octupole (E3) amplitudes to zero as theory predicts for transitions between charmonium S states and P states, we find aJ=2 2 = (−9.3±1.6±0.3)×10−2 and bJ=2 2 = (1.0± 1.3± 0.3)× 10−2. If we allow for E3 amplitudes we find, with a four-parameter fit, aJ=2 2 = (−7.9±1.9±0.3)×10−2, bJ=2 2 = (0.2±1.4±0.4)×10−2, aJ=2 3 = (1.7±1.4±0.3)×10−2, and bJ=2 3 = (−0.8 ± 1.2 ± 0.2) × 10−2. We determine the ratios aJ=1 2 /aJ=2 2 = 0.67 −0.13 and aJ=1 2 /b J=1 2 = −2.27 −0.99, where the theoretical predictions are independent of the charmed quark magnetic moment and are aJ=1 2 /a J=2 2 = 0.676± 0.071 and aJ=1 2 /bJ=1 2 = −2.27± 0.16.
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