Determination of the $\Sigma^{+}$ Timelike Electromagnetic Form Factors

TL;DR

This study measures the electromagnetic form factors of the $oldsymbol{ ext{Sigma}}^{+}$ hyperon in the timelike region at multiple energies, revealing phase information crucial for understanding baryon structure and dynamics.

Contribution

It provides the first exploration of the phase of hyperon electromagnetic form factors across a wide four-momentum transfer range.

Findings

Determined the phase of the $ ext{Sigma}^{+}$ form factors at three energies.

Extracted the relative phase between electric and magnetic form factors.

Provided data essential for understanding baryon asymptotic behavior.

Abstract

Based on data samples collected with the BESIII detector at the BEPCII collider, the process $e^{+}e^{-} \to \Sigma^{+}\bar{\Sigma}^{-}$ is studied at center-of-mass energies $\sqrt{s}$ = 2.3960, 2.6454, and 2.9000 GeV. Using a fully differential angular description of the final state particles, both the relative magnitude and phase information of the $\Sigma^{+}$ electromagnetic form factors in the timelike region are extracted. The relative phase between the electric and magnetic form factors is determined to be $\sin\Delta\Phi$ = -0.67~$\pm$~0.29~(stat)~$\pm$~0.18~(syst) at $\sqrt{s}$ = 2.3960 GeV, $\Delta\Phi$ = 55$^{\circ}$~$\pm$~19$^{\circ}$~(stat) $\pm$~14$^{\circ}$~(syst) at $\sqrt{s}$ = 2.6454 GeV, and 78$^{\circ}$~$\pm$~22$^{\circ}$~(stat) $\pm$~9$^{\circ}$~(syst) at $\sqrt{s}$ = 2.9000 GeV. For the first time, the phase of the hyperon electromagnetic form factors is explored in a wide range of four-momentum transfer. The evolution of the phase along with four-momentum transfer is an important input for understanding its asymptotic behavior and the dynamics of baryons.