First observation of the exclusive decays ${\Lambda }_c^{+}\to \Lambda {\pi }^{+}{\pi }^{+}{\pi }^{-}{\pi }^0$ and ${\Lambda }_c^{+}\to \Lambda \omega {\pi }^{+}$

Using data collected by the CLEO III detector at CESR, we report on the first observation of the decays ${\Lambda }_c^{+}\to \Lambda {\pi }^{+}{\pi }^{+}{\pi }^{-}{\pi }^0$ and ${\Lambda }_c^{+}\to \Lambda \omega {\pi }^{+}.$ The branching fractions are measured relative to the ${\mathrm{pK}}^{-}{\pi }^{+}$ mode; we find $\mathcal{B}({\Lambda }_c^{+}\to \Lambda {\pi }^{+}{\pi }^{+}{\pi }^{-}{\pi }^0)/\mathcal{B}({\Lambda }_c^{+}\to {\mathrm{pK}}^{-}{\pi }^{+})=0.36\mathrm{}\pm 0.09\left(\mathrm{stat}\right)\pm 0.09\left(\mathrm{syst}\right)$ and $\mathcal{B}({\Lambda }_c^{+}\to \Lambda \omega {\pi }^{+})/\mathcal{B}({\Lambda }_c^{+}\to {\mathrm{pK}}^{-}{\pi }^{+})=0.24\mathrm{}\pm 0.06\left(\mathrm{stat}\right)\pm 0.06\left(\mathrm{syst}\right).\mathrm{}$ We also observe a small excess of events in ${\Lambda }_c^{+}\to \Lambda \eta {\pi }^{+},$ $\overrightarrow{\eta }{\pi }^{+}{\pi }^{-}{\pi }^0$ from which we find $\mathcal{B}({\Lambda }_c^{+}\to \Lambda \eta {\pi }^{+})/\mathcal{B}({\Lambda }_c^{+}\to {\mathrm{pK}}^{-}{\pi }^{+})=0.41\mathrm{}\pm 0.17\pm 0.10$ with a corresponding limit of $<0.65\%$ at 90% confidence level. This rate is consistent with previous measurements of ${\Lambda }_c^{+}\to \Lambda \eta {\pi }^{+},$ $\overrightarrow{\eta }\gamma \gamma .$ We find that the combined branching fractions for ${\Lambda }_c^{+}\to \Lambda \omega {\pi }^{+}$ and ${\Lambda }_c^{+}\to \Lambda \eta {\pi }^{+}$ comprise $(87\mathrm{}\pm 13)\%$ of the total ${\Lambda }_c^{+}\to \Lambda {\pi }^{+}{\pi }^{+}{\pi }^{-}{\pi }^0$ rate. We set an upper limit on $\mathcal{B}({\Lambda }_c^{+}\to \Lambda {\pi }^{+}{\pi }^{+}{\pi }^{-}{\pi }^0)/\mathcal{B}({\Lambda }_c^{+}\to {\mathrm{pK}}^{-}{\pi }^{+})$ for non-ω and non-η modes of 0.13 at 90% confidence level.