Observation of the decay ${\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{-}{\pi }^{+}{\pi }^{+}{\pi }^0$

We report the first observation of the decay $\Lambda^+_{c}\rightarrow \Sigma^- \pi^+\pi^+\pi^0$,basedondataobtainedin$e^+e^-$ annihilations with an integrated luminosity of 567~pb${}^{-1}$ at $\sqrt{s}=4.6$~GeV. The data were collected with the BESIII detector at the BEPCII storage rings. The absolute branching fraction $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{-}{\pi }^{+}{\pi }^{+}{\pi }^0)$ is determined to be $(2.11\pm 0.33(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.})\pm 0.14(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.}))\mathrm{\%}$. In addition, an improved measurement of $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\mathrm{\Sigma }}^{-}{\pi }^{+}{\pi }^{+})$ is determined as $(1.81\pm 0.17(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.})\pm 0.09(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.}))\mathrm{\%}$.