Identify the new state $Y(3872)$ as the P-wave DD̄^*/D̄D^* resonance

The BESIII Collaboration recently observed a new charmonium-like vector state $Y(3872)$ in e⁺e⁻→ DD̄, which should be the first P-wave DD̄^*/D̄D^* molecular resonance. The experimental and theoretical identification of the P-wave dimeson state holds paramount importance in enhancing our comprehension of the non-perturbative QCD and few-body physics. Its existence is firmly established in a unified meson-exchange model which simultaneously depicts the features of the χc1(3872), Zc(3900) and Tcc(3875). This scenario can be directly examined in the e⁺e⁻→ DD̄^*/D̄D^* cross section to see whether a resonance exists at the threshold. The credibility of the investigations is also ensured by the fact that the P-wave interaction dominantly arises from the well-known long-range pion exchange. Additionally, the existence of the P-wave resonance only depends on the interaction strength and is less sensitive to the potential shapes. We extensively calculate all systems up to P-wave with various quantum numbers and predict a dense population of the DD̄^*/D̄D^* and DD^* states, where the S-wave DD̄^*/D̄D^* state with IG (JPC)=0⁻ (1⁺⁻), P-wave DD̄^*/D̄D^* state with IG(JPC)=0⁺(0⁻⁺), and P-wave DD^* state with I(JP)=0(0⁻) are more likely to be observed in experiments.