Observation of a near-threshold enhancement in the $\Lambda\bar{\Lambda}$ mass spectrum from $e^+e^-\to\phi\Lambda\bar{\Lambda}$ at $\sqrt{s}$ from 3.51 to 4.60 GeV

TL;DR

This study reports the observation of a near-threshold enhancement in the $ m{ extbf{ extit{ extLambdaar{ extLambda}}}}$ mass spectrum from $e^+e^-$ collisions, revealing a resonance structure and measuring the energy-dependent cross section in the 3.51 to 4.60 GeV range.

Contribution

First measurement of the energy-dependent cross section for $e^+e^- o m{ extbf{ extit{ extLambdaar{ extLambda}}}}$ in this energy region, including observation of a new resonance near the $ m{ extLambdaar{ extLambda}}$ threshold.

Findings

Observed a resonance near the $ m{ extLambdaar{ extLambda}}$ threshold with specific mass and width.

Rejected certain $J^{PC}$ quantum number hypotheses based on helicity angle analysis.

Measured the energy-dependent cross section and explored contributions from excited $ m{ extpsi}$ and $Y$-states.

Abstract

The process $e^+ e^- \to \phi \Lambda \bar{\Lambda}$ is studied using data samples collected with the BESIII detector at the BEPCII collider at center-of-mass energies $\sqrt{s}$ ranging from $3.51$ to $4.60~{\rm GeV}$ . An intermediate resonance structure is observed near the threshold of $\Lambda \bar{\Lambda}$. It has a mass of $(2262 \pm 4 \pm 28)~{\rm{MeV}}/c^{2}$ and a width of $(72 \pm 5 \pm 43)~\rm{MeV}$, where the quoted uncertainties are statistical and systematic, respectively. The $J^{PC}$ quantum numbers of $0^{-+}$ and $0^{++}$ are rejected, while other $J^{PC}$ hypotheses are possible, according to the helicity angle study. The energy-dependent cross section of the $e^+ e^- \to \phi \Lambda \bar{\Lambda}$ process is measured for the first time in this energy region, and contributions from excited $\psi$ states and vector charmonium-like $Y$-states are investigated.