Cheng, Hai-YangHai-YangChengChiang, Cheng-WeiCheng-WeiChiangXu, FanrongFanrongXu2025-08-012025-08-012024-11-26https://scholars.lib.ntu.edu.tw/handle/123456789/730912The internal structure of the light scalar meson a0(980) is explored in the three-body D decays of D→a0(980)P→P1P2P through the intermediate state a0(980), where P denotes a pseudoscalar meson. The quasi-two-body D→a0(980)+P decays are governed by the external W-emission diagram in which a0(980)+ is emitted. The predicted branching fractions in the qq¯ model of a0(980) are too small by one to two orders of magnitude compared to the experiment as the amplitude is suppressed by the smallness of the a0(980)+ decay constant, while those for D+→a0(980)0P and D0→a0(980)-P are usually too large. These discrepancies can be resolved, provided that a0(980) is a tetraquark state. In this case, there exist two additional T-like topological amplitudes, denoted by T¯ and T, which readily account for the discrepancies. An important implication of the tetraquark model is that the Ds+→a0(980)+π0+a0(980)0π+ decay is not a purely W-annihilation process as in the qq¯ model of a0(980); it receives dominant contributions from T¯ newly noticed in this work. Therefore, measurements of (D,Ds+)→a0(980)P decays lend strong support to the tetraquark picture of a0(980).journal article10.1103/physrevd.110.094052