While the light scalar mesons (S0) are considered to be either ordinary \( q\overline{q} \) or exotic tetraquark states, we investigate the semileptonic decays D → S0e+νe, by taking into account the resonant effects of S0 → M1M2, where S0 = a0(980), f0(980), and f0(500)/σ0, and M1(2) represents a pseudoscalar meson. For the first time, the D → S0 form factors in the two quark structures are both presented. Subsequently, we calculate \( \mathcal{B} \) ( \( {D}_s^{+} \) → σ0e+νe, σ0 → π+π−) = (20.3 ± 1.8 ± 0.5) × 10−4 in the \( q\overline{q} \) structure, showing significant 9σ deviations from the experimental upper limit of 3.3 × 10−4. In contrast, \( \mathcal{B} \) ( \( {D}_s^{+} \) → σ0e+νe, σ0 → π+π−) = ( \( {0.58}_{-0.57}^{+1.43} \) ± 0.01) × 10−4 in the \( {q}^2{\overline{q}}^2 \) structure is within the allowed experimental range. Clearly, the light scalar meson is tested as a non- \( q\overline{q} \) state. We hence demonstrate a highly sensitive new approach for exploring the true nature of scalar mesons, which can be extended to non-leptonic D decays as well as B meson decays.
