Pionic transitions of the spin-2 partner of X(3872) to χcJ

We investigated the pionic transitions between the X2 spin-2 partner of the X(3872) and χc1,2 using a nonrelativistic effective field theory. The X2 is assumed to be a bound state of the D* and D¯* mesons and to decay through several kinds of loops, including the bubble, triangle, and box loops. Within the present model, the widths for the single-pion decays X2→π0χcJ are predicted to be about 3–30 keV. For the dipion decays, the widths are a few keVs. These widths yield a branching fraction of 10−3–10−2. The ratio Rc0=Γ(X2→π+π−χcJ)/Γ(X2→π0π0χcJ)≃1.6, which is a bit smaller than the expected value of 2, and R21=Γ(X2→ππχc2)/Γ(X2→ππχc1)≃0.85. These ratios are nearly independent of the X2 mass and the coupling constants, which might be a good quantity for the experiments. Moreover, the invariant mass spectra of the π0χcJ final state for the dipion processes are presented, showing a cusp structure at the DD¯* threshold enhanced and narrowed by the nearby triangle singularity. Published by the American Physical Society 2024