Observation of the decay $X(3872) \to π^0 χ_{c1}(1P)$

Abstract

Using a total of $9.0~\mathrm{fb}^{-1}$ of $e^+e^-$ collision data with center-of-mass energies between 4.15 and 4.30 GeV collected by the BESIII detector, we search for the processes $e^+e^-\to γX(3872)$ with $X(3872)\toπ^0χ_{cJ}$ for $J=0,1,2$. We report the first observation of $X(3872)\toπ^{0}χ_{c1}$, a new decay mode of the $X(3872)$, with a statistical significance of more than 5$σ$. Normalizing to the previously established process $e^+e^-\to γX(3872)$ with $X(3872)\toπ^+π^-J/ψ$, we find ${\cal B}(X(3872) \to π^0 χ_{c1})/{\cal B}(X(3872) \to π^+π^- J/ψ) = 0.88^{+0.33}_{-0.27}\pm0.10$, where the first error is statistical and the second is systematic. We set 90% confidence level upper limits on the corresponding ratios for the decays to $π^0χ_{c0}$ and $π^0χ_{c2}$ of 19 and 1.1, respectively.

8 pages, 4 figures