Regular Article – Theoretical Physics
The cross section of as a litmus test of isospin violation in the decays of vector charmonia into
Laboratori Nazionali di Frascati dell’INFN, Frascati, Italy
2 INFN Sezione di Perugia, 06100, Perugia, Italy
3 Università di Perugia, 06100, Perugia, Italy
Accepted: 12 September 2020
Published online: 29 September 2020
Under the aegis of isospin conservation, the amplitudes in Born approximation, i.e., considering the only one-photon-exchange mechanism, of the decay , where is a vector charmonium, and of the reaction at the mass, are parametrized by the same electromagnetic coupling. It follows that, the modulus of such a coupling can be extracted from the data on the two observables: the decay branching fraction and the annihilation cross section. By considering the first two vector charmonia, and , it is found that, especially in the case of , there is a substantial discrepancy between the values of the modulus of the same electromagnetic coupling extracted from the branching ratio and the cross section. We propose, as a possible explanation for such a disagreement, the presence in the decay amplitude of isospin-violating contributions driven by two different mechanisms, that, however, appear to be more favored in the than in the decays.
© The Author(s) 2020
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