Search for ${\mathrm{\Lambda }}_c^{+}\to \varphi p{\pi }^0$ and branching fraction measurement of ${\mathrm{\Lambda }}_c^{+}\to K^{-}{\pi }^{+}p{\pi }^0$

We have searched for the Cabibbo-suppressed decay ${\mathrm{\Lambda }}_c^{+}\to \varphi p{\pi }^0$ in $e^{+}{e}^{-}$ collisions using a data sample corresponding to an integrated luminosity of $915{\mathrm{fb}}^{-1}$. The data were collected by the Belle experiment at the KEKB $e^{+}{e}^{-}$ asymmetric-energy collider running at or near the $\mathrm{\Upsilon }(4S)$ and $\mathrm{\Upsilon }(5S)$ resonances. No significant signal is observed, and we set an upper limit on the branching fraction of $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to \varphi p{\pi }^0)<15.3\times {10}^{-5}$ at 90% confidence level. The contribution of nonresonant ${\mathrm{\Lambda }}_c^{+}\to K^{+}{K}^{-}p{\pi }^0$ decays is found to be consistent with zero, and the corresponding upper limit on its branching fraction is set to be $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to K^{+}{K}^{-}p{\pi }^0{)}_{\mathrm{NR}}<6.3\times {10}^{-5}$ at 90% confidence level. We also search for an intermediate hidden-strangeness pentaquark decay $P_s^{+}\to \varphi p$. We see no evidence for this intermediate decay and set an upper limit on the product branching fraction of $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to P_s^{+}{\pi }^0)\times \mathcal{B}(P_s^{+}\to \varphi p)<8.3\times {10}^{-5}$ at 90% confidence level. Finally, we measure the branching fraction for the Cabibbo-favored decay ${\mathrm{\Lambda }}_c^{+}\to K^{-}{\pi }^{+}p{\pi }^0$; the result is $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to K^{-}{\pi }^{+}p{\pi }^0)=(4.42\pm 0.05(\text{stat})\pm 0.12(\text{syst})\pm 0.16(\text{norm}))\%$, which is the most precise measurement to date.

Figure 1

Feynman diagram for the decay (a) ${\mathrm{\Lambda }}_c^{+}\to \varphi p{\pi }^0$ and (b) ${\mathrm{\Lambda }}_c^{+}\to P_s^{+}{\pi }^0$.

Figure 2

Projections of the 2D fit: (a) $m(K^{+}{K}^{-}p{\pi }^0)$ and (b) $m(K^{+}{K}^{-})$. The points with the error bars are the data, and the (red) dotted, (green) dashed and (brown) dot-dashed curves represent the combinatorial, signal and nonresonant candidates, respectively, and (blue) solid curves represent the total PDF. The solid curve in (b) completely overlaps the curve for the combinatorial background.

Figure 3

Fit to the invariant mass distribution of $p{K}^{-}{\pi }^{+}$. The points with the error bars are the data, the (red) dotted and (green) dashed curves represent the combinatorial and signal candidates, respectively, and (blue) curve represents the total PDF.

Figure 4

The background-subtracted distribution of $m(\varphi p)$ in the $\varphi p{\pi }^0$ final state. The points with error bars are data, and the (blue) solid line shows the total PDF. The (red) dotted curve shows the fitted phase space component (which has fluctuated negative).

Figure 5

Fit to the invariant mass distribution of $m(K^{-}{\pi }^{+}p{\pi }^0)$. The points with the error bars are the data, the (red) dotted and (green) dashed curves represent the combinatorial and signal candidates, respectively, and (blue) curve represents the total PDF. The ${\chi }^2/(\mathrm{number}\mathrm{of}\mathrm{bins})$ of the fit is 1.43, which indicate that the fit gives a good description of the data.