Measurements of the branching fractions of ${\mathrm{\Lambda }}_c^{+}\to p\eta$ and ${\mathrm{\Lambda }}_c^{+}\to p{\pi }^0$ decays at Belle

We report measurements of the branching fractions of singly Cabibbo-suppressed decays ${\mathrm{\Lambda }}_c^{+}\to p\eta$ and ${\mathrm{\Lambda }}_c^{+}\to p{\pi }^0$ using the full Belle data sample corresponding to an integrated luminosity of $980.6{\mathrm{fb}}^{-1}$. The data were collected by the Belle detector at the KEKB $e^{+}{e}^{-}$ asymmetric energy collider. A clear ${\mathrm{\Lambda }}_c^{+}$ signal is seen in the invariant mass distribution of $p\eta$. The fitted number of signal events of the ${\mathrm{\Lambda }}_c^{+}\to p\eta$ process is $7734\pm 263$; from this, we measure the ratio of branching fractions $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p\eta )/\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+})=[2.258\pm 0.077(\mathrm{stat})\pm 0.122(\mathrm{syst})]\times {10}^{-2}$, from which we infer the branching fraction $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p\eta )=[1.42\pm 0.05(\mathrm{stat})\pm 0.11(\mathrm{syst})]\times {10}^{-3}$. In addition, no significant signal for ${\mathrm{\Lambda }}_c^{+}\to p{\pi }^0$ is found, so an upper limit on the branching fraction of $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p{\pi }^0)<8.0\times {10}^{-5}$ at a 90% credibility level is set, more than 3 times better than the best current upper limit.

Figure 1

Feynman diagrams for the weak Cabibbo-suppressed decays ${\mathrm{\Lambda }}_c^{+}\to p{\pi }^0$ and ${\mathrm{\Lambda }}_c^{+}\to p\eta$. (a),(b) internal $W$ emission, (c),(d),(e) $W$ exchange, and (f) internal $W$ emission for ${\mathrm{\Lambda }}_c^{+}\to p\eta$.

Figure 2

Fit to the invariant mass distribution of $p{K}^{-}{\pi }^{+}$ from data. Black dots with error bars represent the data; the pink dashed line, the blue dash-dotted line, the green dashed line, and the red solid line represent the background contribution, the core Gaussian, tail Gaussian, and the total fit, respectively.

Figure 3

Fit to the invariant mass distribution of $p\eta$ from data. Black dots with error bars represent the data; the magenta dash-dotted line, the blue dashed line, and the red solid line represent the background component, the signal, and the total fit, respectively.

Figure 4

Fit to the invariant mass distribution of $p{\pi }^0$. Black dots with error bars represent the data; the magenta dash-dotted line, the blue dashed line, and the red solid line represent the background component, the signal, and the total fit, respectively.

Figure 5

Dalitz plot of the selected ${\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+}$ candidates.

Figure 6

Dalitz plot of efficiency distribution for ${\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+}$ decay.

Figure 7

The likelihood distribution as a function of the branching fraction for ${\mathrm{\Lambda }}_c^{+}\to p{\pi }^0$ with the systematic uncertainty included. The blue arrow refers to the 90% C.L. upper limit on the branching fraction.