$X(3872)$, $X_b$, and the $\chi_{b1}(3P)$ state

Abstract

We discuss the possible production and discovery channels in $e^+e^-$ and $pp$ machines of the $X_b$, the bottomonium counterpart of $X(3872)$ and the putative isoscalar analogue of the charged bottomonium-like states $Z_b$ discovered by Belle. We suggest that the $X_b$ may be close in mass to the bottomonium state $\chi_{b1}(3P)$, mixing with it and sharing its decay channels, just as $X(3872)$ is likely a mixture of a $\bar D D^*$ molecule and $\chi_{c1}(2P)$. Consequently, the experiments which reported observing $\chi_{b1}(3P)$ might have actually discovered the $X_b$, or a mixture of the two states.