The $\bar{B}^0 \to D^{*+} \bar{D}^{*0} K^-$ reaction to detect the $I=0, J^P=1^+$ partner of the $X_0(2866)$

Abstract: We have chosen the $$\bar{B}⁰ \to D^{*+} \bar{D}^{*0} K<sup>-$$ reaction in order to observe the $I=0, J<sup>P=1<sup>+$ ($R_1$) partner state of the $X_0(2866)$ stemming from the $D<sup><em>\bar{K}^</em>$ molecular picture. The reaction proceeds via external emission in the most favored Cabibbo decay mode and one observes the $R_1$ state as a very strong peak versus the background in the $D^{*+} K<sup>-$ spectrum. The branching ratio for $R_1$ production in this reaction is estimated of the order of $4\times 10<sup>{-3}$. The method used, applied to the $$B⁺ \to D^- D⁺ K<sup>+$$ reaction, produces a ratio of signal to background in the $D^- K<sup>+$ spectrum in very good agreement with the LHCb experiment that observed the $X_0(2866)$.