Measurement of $\psi(3686)\to\Lambda\bar{\Lambda}\eta$ and $\psi(3686)\to\Lambda\bar{\Lambda}\pi^0$ decays

TL;DR

This study reports the first evidence of the isospin-violating decay $oldsymbol{ oar{ ext{Lambda}} ext{Lambda} ext{pi}^0}$ and measures branching fractions for both $oldsymbol{ oar{ ext{Lambda}} ext{Lambda} ext{eta}}$ and $oldsymbol{ oar{ ext{Lambda}} ext{Lambda} ext{pi}^0}$ decays using a large sample of $oldsymbol{ ext{psi}(3686)}$ events.

Contribution

It provides the first evidence of the isospin-violating decay $oldsymbol{ oar{ ext{Lambda}} ext{Lambda} ext{pi}^0}$ and measures its branching fraction, along with analyzing the $oldsymbol{ oar{ ext{Lambda}} ext{Lambda} ext{eta}}$ decay.

Findings

Evidence of $oldsymbol{ oar{ ext{Lambda}} ext{Lambda} ext{pi}^0}$ decay with $3.7σ$ significance.

Branching fraction of $oldsymbol{ oar{ ext{Lambda}} ext{Lambda} ext{pi}^0}$ is $(1.42 extpm0.39 extpm0.59) imes10^{-6}$.

Branching fraction of $oldsymbol{ oar{ ext{Lambda}} ext{Lambda} ext{eta}}$ is $(2.34 extpm0.18 extpm0.52) imes10^{-5}$.

Abstract

Based on a sample of $448.1\times10^6\ \psi(3686)$ events collected with the BESIII detector, a study of $\psi(3686)\to\Lambda\bar{\Lambda}\pi^0$ and $\psi(3686)\to\Lambda\bar{\Lambda}\eta$ is performed. Evidence of the isospin-violating decay $\psi(3686)\to\Lambda\bar{\Lambda}\pi^0$ is found for the first time with a statistical significance of $3.7\sigma$, the branching fraction $\mathcal{B}(\psi(3686)\to\Lambda\bar{\Lambda}\pi^0)$ is measured to be $(1.42\pm0.39\pm0.59)\times10^{-6}$, and its corresponding upper limit is determined to be $2.47\times10^{-6}$ at 90\% confidence level. A partial wave analysis of $\psi(3686)\to\Lambda\bar{\Lambda}\eta$ shows that the peak around $\Lambda\eta$ invariant mass threshold favors a $\Lambda^*$ resonance with mass and width in agreement with the $\Lambda(1670)$. The branching fraction of the $\psi(3686)\to\Lambda\bar{\Lambda}\eta$ is measured to be $(2.34\pm0.18\pm0.52)\times10^{-5}$. The first uncertainties are statistical and the second are systematic.