Observation of the Singly Cabibbo-Suppressed Decay $\Lambda_{c}^{+} \to n\pi^{+}$

TL;DR

This paper reports the first observation of the decay $ pi$ of the $ ext{Lambda}_c^+$ baryon, measures its branching fraction, and compares it with theoretical predictions, also providing measurements of related decay modes.

Contribution

It presents the first observation and measurement of the $ pi$ decay of $ ext{Lambda}_c^+$, challenging existing phenomenological models with a new branching ratio.

Findings

First observation of $ pi$ decay with 7.3$\sigma$ significance.

Measured branching fraction of $ pi$ is $(6.6 o1.2_{ m stat} o0.4_{ m syst}) imes 10^{-4}$.

The ratio of branching fractions exceeds 7.2 at 90 ext{% CL}, contradicting current models.

Abstract

The singly Cabibbo-suppressed decay $\Lambda_{c}^{+} \to n\pi^{+}$ is observed for the first time with a statistical significance of $7.3\sigma$ by using 3.9 $\mathrm{fb}^{-1}$ of $e^{+}e^{-}$ collision data collected at center-of-mass energies between 4.612 and 4.699 GeV with the BESIII detector at BEPCII. The branching fraction of $\Lambda_{c}^{+} \to n\pi^{+}$ is measured to be $(6.6\pm1.2_{\rm stat}\pm0.4_{\rm syst})\times 10^{-4}$. By taking the upper limit of branching fractions of $\Lambda_{c}^{+} \to p\pi^0$ from the Belle experiment, the ratio of branching fractions between $\Lambda_{c}^{+} \to n\pi^{+}$ and $\Lambda_{c}^{+} \to p\pi^0$ is calculated to be larger than 7.2 at the 90% confidence level, which disagrees with the current predictions of available phenomenological models. In addition, the branching fractions of the Cabibbo-favored decays $\Lambda_{c}^{+} \to \Lambda\pi^{+}$ and $\Lambda_{c}^{+} \to \Sigma^{0}\pi^{+}$ are measured to be $(1.31\pm0.08_{\rm stat}\pm0.05_{\rm syst})\times 10^{-2}$ and $(1.22\pm0.08_{\rm stat}\pm0.07_{\rm syst})\times 10^{-2}$, respectively, which are consistent with previous results.