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 $6.32\text{}\text{}{\mathrm{fb}}^{-1}$. This decay is expected to be sensitive to ${\pi }^{0}–\eta $ mixing. No significant signal is observed. We set an upper limit of $6.4×{10}^{-5}$ on the branching fraction at the 90% confidence level.