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Open charm contributions to the E1 transitions of $ψ(3686)$ and $ψ(3770)\to γχ_{cJ}$

The E1 transitions of $ψ(3686)$ and $ψ(3770)\to γχ_{cJ}$ are investigated in a non-relativistic effective field theory (NREFT) where the open charm effects are included systematically as the leading corrections. It also allows a self-consistent inclusion of the $S$-$D$ mixing in the same framework. We are able to show that the open charm contributions are essential for understanding the significant discrepancies between the non-relativistic leading order calculations and the experimental data.