Search for the semileptonic decay $D_s^{+}\to {\pi }^0{e}^{+}{\nu }_e$

We present the first search for the semileptonic decay $D_s^{+}\to {\pi }^0{e}^{+}{\nu }_e$ using a data sample of electron-positron collisions recorded with the BESIII detector at center-of-mass energies between 4.178 and 4.226~GeV, corresponding to an integrated luminosity of 6.32~fb${}^{-1}$. This decay is expected to be sensitive to ${\pi }^0$–$\eta$ mixing. No significant signal is observed. We set an upper limit of $6.4\times {10}^{-5}$ on the branching fraction at the $90\mathrm{\%}$ confidence level.