Two-photon width of etac and eta'c from Heavy-Quark Spin Symmetry
Abstract
We evaluate the two-photon width of the pseudoscalar charmonia, Gamma(etac -> gamma gamma) and Gamma(eta'c -> gamma gamma), within a Heavy-Quark Spin-Symmetry setting and show that whereas the former agrees with experiment, the latter is more than twice larger than the recent measurement by CLEO. When binding-energy effects are included in the eta'c case, the discrepancy is worse, pointing out at a possible anomaly in the eta'c decay.
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