Observation of ${\mathrm{\Lambda }}_c^{+}\to n{K}_S^0{\pi }^{+}$

We report the first direct measurement of decays of the ${\mathrm{\Lambda }}_c^{+}$ baryon involving the neutron. The analysis is performed using $567{\mathrm{pb}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected at $\sqrt{s}=4.599\mathrm{GeV}$ with the BESIII detector at the BEPCII collider. We observe the decay ${\mathrm{\Lambda }}_c^{+}\to n{K}_S^0{\pi }^{+}$ and measure the absolute branching fraction to be $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to n{K}_S^0{\pi }^{+})=[1.82\pm 0.23(\text{stat})\pm 0.11(\text{syst})]\%$. A comparison to $\mathcal{B}[{\mathrm{\Lambda }}_c^{+}\to p(\overline{K}\pi {)}^0]$ provides an important test of isospin symmetry and final state interactions.

Figure 1

Scatter plot of $M_{{\pi }^{+}{\pi }^{-}}$ vs $M_{\text{miss}}^2$ for ${\mathrm{\Lambda }}_c^{+}\to n{K}_S^0{\pi }^{+}$ observed from data.

Figure 2

Simultaneous fit to $M_{\text{miss}}^2$ and $M_{{\pi }^{+}{\pi }^{-}}$ of events in (a),(b) the ${\overline{\mathrm{\Lambda }}}_c^{-}$ signal region and (c),(d) sideband regions. Data are shown as the dots with error bars. The long-dashed lines (blue) show the ${\mathrm{\Lambda }}_c^{+}$ backgrounds while the dot-dashed curves (pink) show the non-${\mathrm{\Lambda }}_c^{+}$ backgrounds. The (red) solid curves show the total fit. The (yellow) shaded area show the MC simulated backgrounds from ${\mathrm{\Lambda }}_c^{+}$ decay.