Novel method to extract the femtometer structure of strange baryons using the vacuum polarization effect

TL;DR

This paper introduces a new method leveraging vacuum polarization effects at the J/ψ resonance to precisely determine the femtometer-scale structure of strange baryons, using extensive BESIII data.

Contribution

The novel approach exploits cross section enhancement at the J/ψ resonance to measure hyperon form factors with unprecedented precision.

Findings

Measured form factor ratio R = 0.860 ± 0.029 (stat.) ± 0.010 (syst.)

Determined phase differences ΔΦ₁ and ΔΦ₂ with high accuracy

First investigation of CP symmetry in this hyperon-antihyperon production

Abstract

One of the fundamental goals of particle physics is to gain microscopic understanding of the strong interaction. Electromagnetic form factors quantify the structure of hadrons in terms of charge and magnetization distributions. While the nucleon structure has been investigated extensively, data on hyperons is still scarce. It has recently been demonstrated that electron-positron annihilations into hyperon-antihyperon pairs provide a powerful tools to investigate their inner structure. We present a novel method useful for hyperon-antihyperon pairs of different types which exploits the cross section enhancement due to the vacuum polarization effect at the $J/\psi$ resonance. Using the 10 billion $J/\psi$ events collected with the BESIII detector, this allows a thorough determination of the hyperon structure . The result is essentially a precise snapshot of a $\bar\Lambda\Sigma^0$~($\Lambda\bar\Sigma^0$) pair in the making, encoded in the form factor ratio and the phase. Their values are measured to be $R = 0.860\pm0.029({\rm stat.})\pm0.010({\rm syst.})$, $\Delta\Phi_1=(1.011\pm0.094({\rm stat.})\pm0.010({\rm syst.}))~\rm rad$ for $\bar\Lambda\Sigma^0$ and $\Delta\Phi_2=(2.128\pm0.094({\rm stat.})\pm0.010({\rm syst.}))~\rm rad$ for $\Lambda\bar\Sigma^0$, respectively. Furthermore, charge-parity (CP) breaking is investigated for the first time in this reaction and found to be consistent with CP symmetry.