$η_c$ production associated with light hadrons at the B-factories and the future super B-factories

We present a complete study of the associated production of the $η_c$ meson with light hadrons in $e^+e^-$ collisions at the B-factory energy, which is demonstrated to be one of the best laboratories for testing the colour-octet (CO) mechanism. The colour-siglet contributions are evaluated up to $O(α^2α_s^3)$ while the CO ones are evaluated up to $O(α^2α_s^2)$. For the first time, the angular distribution of the $^1S_0^{[8]}$ production is studied at QCD next-to-leading order. We find that the $^1S_0^{[8]}$ channel dominate the total cross section, while the $^1P_1^{[8]}$ one exhibit its importance in the angular distribution, which turns out to be downward going with respect to $\mathrm{cos}θ$. This can be considered as the most distinct signal for the CO mechanism.

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