Tentative estimates of $\mathcal{B}(X(3872)\to\pi^0\pi^0\chi_{c1})$ and $\mathcal{B}(X(3872)\to\pi^+\pi^-\chi_{c1})$

Abstract

The rates of the $X(3872)\to\pi^0\pi^0\chi_{c1}$ and $X(3872)\to \pi^+\pi^-\chi_{c1}$ decays are estimated in the model of the triangle loop diagrams with charmed $D^*\bar DD$ and $\bar D^*D\bar D$ mesons in the loops. There are the triangle logarithmic singularities in the physical region of the $X(3872)\to\pi^0\pi^0 \chi_{c1}$ decay which manifest themselves as narrow peaks in the $\pi^0\chi_{c1}$ mass spectrum near the $D^0\bar D^0$ threshold. The model predicts approximately the same branching fractions of the $X(3872)\to\pi^0\pi^0 \chi_{c1}$ and $X(3872)\to\pi^+\pi^-\chi_{c1}$ decays at the level of about (0.8-1.7)$\times10^{-4}$. A distinct prediction of the model is the value of the ratio $\mathcal{R}= \mathcal{B}(X(3872)\to\pi^+\pi^-\chi_{c1})/\mathcal{B}(X(3872) \to\pi^0\pi^0\chi_{c1})\approx1.1$. It weakly depends on the $X(3872)$ resonance parameters and indicates a significant violation of the isotopic symmetry according to which one would expect $\mathcal{R}=2$.