Unexpected features of e+e-->ppbar and e+e-->lambda-lambdabar cross sections near threshold

TL;DR

This paper analyzes BaBar data on e+e- to baryon-antibaryon cross sections near threshold, revealing unexpected non-zero cross sections at threshold due to Coulomb interactions and quark electromagnetic effects, with implications for baryon form factors.

Contribution

It presents a detailed interpretation of unexpected non-vanishing cross sections at threshold, highlighting Coulomb and quark electromagnetic interactions as key factors.

Findings

Coulomb final state interactions dominate proton-antiproton cross section.

Form factor |G^p(4M^2_p)|~1 near threshold.

Non-zero cross section at threshold for neutral baryons explained by quark interactions.

Abstract

Unexpected features of the BaBar data on e+e- in baryon-antibaryon cross sections are discussed. These data have been collected, with unprecedented accuracy, by means of the initial state radiation technique, which is particularly suitable in giving good acceptance and energy resolution at threshold. A striking feature observed in the BaBar data is the non-vanishing cross section at threshold for all these processes. This is the expectation due to the Coulomb enhancement factor acting on a charged fermion pair. In the case of e+e- in proton-antiproton it is found that Coulomb final state interactions largely dominate the cross section and the form factor is |G^p(4M^2_p)|~1, which could be a general feature for baryons. In the case of neutral baryons an interpretation of the non-vanishing cross section at threshold is suggested, based on quark electromagnetic interaction and taking into account the asymmetry between attractive and repulsive Coulomb factors. Besides strange baryon cross sections are compared to U-spin invariance predictions.