First observation of ${\mathrm{\Lambda }}_c(2595{)}^{+}\to {\mathrm{\Lambda }}_c^{+}{\pi }^0{\pi }^0$ and ${\mathrm{\Lambda }}_c(2625{)}^{+}\to {\mathrm{\Lambda }}_c^{+}{\pi }^0{\pi }^0$

By analysing $e^{+}{e}^{-}$ annihilation data corresponding to an integrated luminosity of 368.48~pb${}^{-1}$ collected at the centre-of-mass energies of $\sqrt{s}=4.918$ and $4.951$~GeV with the BESIII detector, we report the first observation of ${\mathrm{\Lambda }}_c(2595{)}^{+}$ and ${\mathrm{\Lambda }}_c(2625{)}^{+}\to {\mathrm{\Lambda }}_c^{+}{\pi }^0{\pi }^0$ with statistical significances of 7.9$\sigma$ and 11.8$\sigma$, respectively. The branching fractions of ${\mathrm{\Lambda }}_c(2595{)}^{+}$ and ${\mathrm{\Lambda }}_c(2625{)}^{+}\to {\mathrm{\Lambda }}_c^{+}{\pi }^0{\pi }^0$ are measured to be $(59.5\pm {11.1}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.}}\pm {7.9}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.}})\mathrm{\%}$ and $(41.0\pm {5.2}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.}}\pm {3.3}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.}})\mathrm{\%}$, respectively. The absolute branching fraction of ${\mathrm{\Lambda }}_c(2595{)}^{+}$ is consistent with the expectation of the mechanism referred to as the threshold effect, proposed for the strong decays of ${\mathrm{\Lambda }}_c(2595{)}^{+}$ within uncertainty.