Cross section of the process $e^+e^-\to n\bar{n}$ near the threshold

TL;DR

This study measures the cross section of electron-positron annihilation into neutron-antineutron pairs near threshold energies, revealing the energy dependence of the form factor and cross section with high precision.

Contribution

It provides the first detailed measurement of the $e^+e^- o nar{n}$ cross section near threshold at multiple energies using the VEPP-2000 collider and specialized timing detection methods.

Findings

Cross section measured to be 0.4--0.6 nb near threshold.

Neutron form factor varies from 0.3 to 0.6 in the studied energy range.

Data improves understanding of nucleon electromagnetic structure.

Abstract

The $e^+e^-\to n\bar{n}$ cross section was measured at center of mass (c.m.) energies from the threshold to 1908 MeV. The experiment to measure the cross section has been carried out at the VEPP-2000 $e^+e^-$ collider in 13 energy points. The SND detector is used to detect the produced neutron-antineutrons ($n\bar{n}$) events. A special time measurement system on the calorimeter was used to select the time-delayed $n\bar{n}$ events. The measured $e^+e^-\to n\bar{n}$ cross section is 0.4--0.6 nb. The neutron effective timelike form factor in the energy range under study varies from 0.3 to 0.6.