Measurement of $e^+e^-\rightarrow\Lambda\bar{\Lambda}\eta$ from 3.5106 to 4.6988 GeV and study of $\Lambda\bar{\Lambda}$ mass threshold enhancement

TL;DR

This study measures the cross section of the process $e^+e^-\rightarrow\Lambda\bar{\Lambda}\eta$ across a range of energies, observes a new enhancement near the $\\\Lambda\bar{\Lambda}$ threshold, and characterizes its properties.

Contribution

First observation of a $\\Lambda\bar{\Lambda}$ mass threshold enhancement in $e^+e^-\rightarrow\Lambda\bar{\Lambda}\eta$ with detailed measurement of its mass and width.

Findings

No significant structure in the cross section line shape.

First observation of the $\\Lambda\bar{\Lambda}$ threshold enhancement.

Mass and width of the enhancement are measured as 2356 MeV/$c^2$ and 304 MeV, respectively.

Abstract

Using data samples with a total integrated luminosity of approximately 18 fb$^{-1}$ collected by the BESIII detector operating at the BEPCII, the process $e^+e^-\rightarrow\Lambda\bar{\Lambda} \eta$ is studied at center-of-mass energies between 3.5106 and 4.6988 GeV. The Born cross section for the process $e^+e^-\rightarrow\Lambda\bar{\Lambda}\eta$ is measured. No significant structure is observed in the Born cross section line shape. An enhancement near the $\Lambda\bar{\Lambda}$ mass threshold is observed for the first time in the process. The structure can be described by an $S$-wave Breit-Wigner function. Neglecting contribution of excited $\Lambda$ states and potential interferences, the mass and width are determined to be ($2356\pm 7\pm17$) MeV/$c^2$ and ($304\pm28\pm54$) MeV, respectively, where the first uncertainties are statistical and the second are systematic.