First Observation of the Semileptonic Decay $\Lambda_c^+\rightarrow pK^- e^+\nu_e$

TL;DR

This paper reports the first observation of the semileptonic decay $oldsymbol{ ext{Λ}_c^+ ightarrow pK^- e^+ u_e}$, measuring its branching fraction and providing evidence for related decays, thereby enhancing understanding of charm baryon semileptonic decays.

Contribution

It presents the first observation and measurement of the branching fraction of $ ext{Λ}_c^+ ightarrow pK^- e^+ u_e$, and evidence for related decay modes, expanding knowledge of charm baryon semileptonic decays.

Findings

Observation of $ ext{Λ}_c^+ ightarrow pK^- e^+ u_e$ with 8.2σ significance.

Measurement of $ ext{Λ}_c^+ ightarrow pK^- e^+ u_e$ branching fraction as $(0.88 extpm0.17_{ m stat} extpm0.07_{ m syst}) imes 10^{-3}$.

Evidence for $ ext{Λ}_c^+ ightarrow ext{Λ}(1520) e^+ u_e$ and $ ext{Λ}_c^+ ightarrow ext{Λ}(1405) e^+ u_e$ with significances of 3.3σ and 3.2σ.

Abstract

Using $4.5~\mathrm{fb}^{-1}$ of $e^+e^-$ annihilation data samples collected at the center-of-mass energies ranging from 4.600~GeV to 4.699~GeV with the BESIII detector at the BEPCII collider, a first study of the semileptonic decays $\Lambda_c^+\rightarrow pK^-e^+\nu_e$, $\Lambda_c^+\rightarrow \Lambda(1520) e^+\nu_e$ and $\Lambda_c^+\rightarrow \Lambda(1405) e^+\nu_e$ is performed. The $\Lambda_c^+\rightarrow pK^-e^+\nu_e$ decay is observed with a significance of $8.2\sigma$ and the branching fraction is measured to be $\mathcal{B}(\Lambda_c^+\rightarrow pK^- e^+\nu_e)=(0.88\pm0.17_{\rm stat.}\pm0.07_{\rm syst.})\times 10^{-3}$. We also report evidence of $\Lambda_c^+\rightarrow \Lambda(1520)e^+\nu_e$ and $\Lambda_c^+\rightarrow \Lambda(1405)e^+\nu_e$ with significances of $3.3\sigma$ and $3.2\sigma$, respectively, and measure $\mathcal B(\Lambda^+_c\rightarrow \Lambda(1520)e^+\nu_e)=(1.02\pm0.52_{\rm stat.}\pm0.11_{\rm syst.})\times10^{-3}$ and $\mathcal B(\Lambda^+_c\rightarrow \Lambda(1405)[\rightarrow pK^-]e^+\nu_e)=(0.42\pm0.19_{\rm stat.}\pm0.04_{\rm syst.})\times10^{-3}$. Combining these with the inclusive semileptonic $\Lambda_c^+$ branching fraction measured by BESIII, the relative fraction is determined to be $[\mathcal{B}(\Lambda_c^+\rightarrow pK^-e^+\nu_e)/\mathcal{B}(\Lambda_c^+\rightarrow X e^+\nu_e)]=(2.1\pm0.4_{\rm stat.}\pm0.2_{\rm syst.})\%$, which provides a clear confirmation that semileptonic $\Lambda_c^+$ decays are not saturated by the $\Lambda \ell^+\nu_{\ell}$ final state.