Timelike electromagnetic form factors of hyperons at large $q^2$

TL;DR

This paper extends a covariant quark model to predict timelike electromagnetic form factors of hyperons at high momentum transfer, aligning well with existing data and guiding future experiments.

Contribution

The novel extension of a covariant quark model from spacelike to timelike regions without additional parameters is the key innovation.

Findings

Model predictions agree with CLEO and BESIII data for certain hyperons at high $q^2$.

Upcoming experiments can further test the model's predictions.

Current data range is insufficient for definitive validation.

Abstract

In the last few years there has been considerable progress in the study of the electromagnetic form factors of baryons in the timelike region, through electron-positron scattering, with increasing squared transfer momentum $q^2$. The modulus of the electric ($G_E$) and magnetic ($G_M$) form factors has been measured for nucleons, hyperons and other baryons at BaBar, CLEO, Belle and BESIII. The novel measurements motivated the extension of a covariant quark model, developed to the spacelike region ($q^2 \le 0$), to the timelike region, without any further parameter fitting. The extension is based on asymptotic relations derived from analyticity and unitarity, valid for the large-$q^2$ region. We use the model to make predictions for the effective form factor $|G|$ (combination of $G_E$ and $G_M$) and the ratio $|G_E/G_M|$ for spin 1/2 hyperons at large $q^2$ (above 10 GeV$^2$). Our calculations are in good agreement with the data from CLEO and BESIII for $\Lambda$, $\Sigma^+$ and $\Xi^-$ above $q^2=15$ GeV$^2$. Upcoming data for $\Sigma^0$, $\Sigma^-$ and $\Xi^-$ at large $q^2$ may be used to further test our predictions. We also compare our model calculations with the scarce available data for $|G_E/G_M|$. We conclude that the present $q^2$ range is not large enough to test our calculations, but that a more definitive test can be made by experiments above $q^2=20$ GeV$^2$.