Measurement of branching fractions for ${\mathrm{\Lambda }}_c^{+}\to n{K}_S^0{\pi }^{+}$ and ${\mathrm{\Lambda }}_c^{+}\to n{K}_S^0{K}^{+}$

Based on $4.5{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data accumulated at center-of-mass energies between 4599.53 and 4698.82 MeV with the BESIII detector, we measure the absolute branching fraction of the Cabibbo-favored decay ${\mathrm{\Lambda }}_c^{+}\to n{K}_S^0{\pi }^{+}$ with the precision improved by a factor of 2.8 and report the first evidence for the singly-Cabibbo-suppressed decay ${\mathrm{\Lambda }}_c^{+}\to n{K}_S^0{K}^{+}$. The branching fractions for ${\mathrm{\Lambda }}_c^{+}\to n{K}_S^0{\pi }^{+}$ and ${\mathrm{\Lambda }}_c^{+}\to n{K}_S^0{K}^{+}$ are determined to be $(1.86\pm 0.08\pm 0.04)\times {10}^{-2}$ and $(3.9_{-1.4}^{+1.7}\pm 0.3)\times 10^{-4}$, respectively, where the first uncertainties are statistical and the second ones are systematic.

Figure 1

Topological diagrams for (a)–(c) ${\mathrm{\Lambda }}_c^{+}\to n{\overline{K}}^0{\pi }^{+}$ and (d),(e) ${\mathrm{\Lambda }}_c^{+}\to n{\overline{K}}^0{K}^{+}$.

Figure 2

The top and bottom sections in each of the four plots show data from the signal and sideband regions in $M_{\mathrm{BC}}$, respectively. The black dots with error bars represent data, the green solid lines represent the total fit results, the blue dashed lines represent the signal shapes, and the magenta dashed (solid) lines represent the non-${\mathrm{\Lambda }}_c^{+}$ backgrounds in signal (sideband) region. For ${\mathrm{\Lambda }}_c^{+}\to n{K}_S^0{\pi }^{+}$, the peaking and flat backgrounds from ${\mathrm{\Lambda }}_c^{+}$ decays are represented by the red and teal dashed lines, respectively. For ${\mathrm{\Lambda }}_c^{+}\to n{K}_S^0{K}^{+}$, the ${\mathrm{\Lambda }}_c^{+}$ backgrounds are represented by the red dashed lines. All these signal and background components are drawn separately.