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Measurements of the branching fractions of $\Lambda_{c}^{+} \rightarrow p \pi^{-} \pi^{+}$, $\Lambda_{c}^{+} \rightarrow p K^{-} K^{+}$, and $\Lambda_{c}^{+} \rightarrow p \pi^{-} K^{+}$

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Abstract

The ratios of the branching fractions of the decays $\Lambda_{c}^{+} \rightarrow p \pi^{-} \pi^{+}$, $\Lambda_{c}^{+} \rightarrow p K^{-} K^{+}$, and $\Lambda_{c}^{+} \rightarrow p \pi^{-} K^{+}$ with respect to the Cabibbo-favoured $\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+}$ decay are measured using proton-proton collision data collected with the LHCb experiment at a 7 TeV centre-of-mass energy and corresponding to an integrated luminosity of 1.0 fb$^{-1}$: \begin{align*} \frac{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p \pi^{-} \pi^{+})}{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})} & = (7.44 \pm 0.08 \pm 0.18) \%, \frac{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} K^{+})}{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})} &= (1.70 \pm 0.03 \pm 0.03) \%, \frac{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p \pi^{-} K^{+})}{\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})} & = (0.165 \pm 0.015 \pm 0.005 ) \%, \end{align*} where the uncertainties are statistical and systematic, respectively. These results are the most precise measurements of these quantities to date. When multiplied by the world-average value for $\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})$, the corresponding branching fractions are \begin{align*} \mathcal{B}(\Lambda_{c}^{+} \rightarrow p \pi^{-} \pi^{+}) &= (4.72 \pm 0.05 \pm 0.11 \pm 0.25) \times 10^{-3}, \mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} K^{+}) &= (1.08 \pm 0.02 \pm 0.02 \pm 0.06) \times 10^{-3}, \mathcal{B}(\Lambda_{c}^{+} \rightarrow p \pi^{-} K^{+}) &= (1.04 \pm 0.09 \pm 0.03 \pm 0.05) \times 10^{-4}, \end{align*} where the final uncertainty is due to $\mathcal{B}(\Lambda_{c}^{+} \rightarrow p K^{-} \pi^{+})$.

Figures and captions

Weak decays of $\Lambda ^+_ c $ to a proton and two mesons, without hyperon mediation. Shown are external $ W $ -emission for (a) $\Lambda ^+_ c \rightarrow p K ^- \pi ^+ $ and (b) $\Lambda ^+_ c \rightarrow p \pi ^- K ^+ $ , internal $ W $ -emission for (c) $\Lambda ^+_ c \rightarrow p K ^- \pi ^+ $ and (d) $\Lambda ^+_ c \rightarrow p \pi ^- K ^+ $ , and $ W $ -exchange for (e) $\Lambda ^+_ c \rightarrow p K ^- \pi ^+ $ .

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Invariant mass distributions of (a) $\Lambda ^+_ c \rightarrow p K ^- \pi ^+ $ , (b) $\Lambda ^+_ c \rightarrow p \pi ^- \pi ^+ $ , (c) $\Lambda ^+_ c \rightarrow p K ^- K ^+ $ , and (d) $\Lambda ^+_ c \rightarrow p \pi ^- K ^+ $ decays, with fit results superimposed. The hatched magenta region indicates the signal, the shaded green region indicates the background from unrelated tracks, and the solid red line indicates the full fit.

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Invariant mass distributions for (a) $\Lambda ^+_ c \rightarrow p K ^- \pi ^+ $ , (c) $\Lambda ^+_ c \rightarrow p \pi ^- \pi ^+ $ , (e) $\Lambda ^+_ c \rightarrow p K ^- K ^+ $ in the prompt analysis, with fit results superimposed. The $\ln \left(\chi^2 _{\mathrm{IP} } \right)$ distributions for (b) $\Lambda ^+_ c \rightarrow p K ^- \pi ^+ $ , (d) $\Lambda ^+_ c \rightarrow p \pi ^- \pi ^+ $ , (f) $\Lambda ^+_ c \rightarrow p K ^- K ^+ $ , with the fit results superimposed, showing the differentiation of prompt and secondary $\Lambda ^+_ c $ .

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Animated gif made out of all figures.

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Tables and captions

Selection efficiency ratios in the prompt and SL measurements, with their associated systematic uncertainties. $\epsilon_{\mathrm{CF}} / \epsilon_{\mathrm{CS}} $ denotes the ratio of the Cabibbo-favoured selection efficiency over that of the Cabibbo-suppressed mode.

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Signal yields in both the SL and prompt measurements.

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Relative systematic uncertainties in each ratio of branching fractions, for the SL analysis.

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Relative systematic uncertainties in each ratio of branching fractions, for the prompt analysis.

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Created on 11 July 2020.