Study of light scalar mesons through $D_s^+ \to π^0 π^0 e^+ ν_e$ and $K_S^0 K_S^0 e^+ ν_e$ decays

Abstract: Using 6.32~fb$^{-1}$ of $e^+e-$ collision data recorded by the BESIII detector at center-of-mass energies between $4.178$ to $4.226$ GeV, we present the first measurement of the decay $D_s^+\to f_0(980)e^{+\nu_e,\,f_0(980)\to} \pi^0\pi0$. The product branching fraction of $D_s^+\to f_0(980)e^{+\nu_e,\,f_0(980)\to} \pi^0\pi0$ is measured to be $(7.9\pm1.4_{\rm stat} \pm0.3_{\rm syst})\times 10^{-4}$, with a statistical significance of $7.8\sigma$. Furthermore, the upper limits on the product branching fractions of $D_s^+\to f_0(500)e^+\nu_e$ with $f_0(500)\to \pi^0\pi0$ and the branching fraction of $D_s^+\to K_{S}^{{0}K_{S}{0}e+\nu_e$} are set to be $7.3\times 10^{-4}$ and $3.8\times 10^{-4}$ at 90\% confidence level, respectively. Our results provide valuable inputs to the understanding of the structures of light scalar mesons.