The KLOE-2 collaboration, analysing the data collected at the DAFNE Collider, has measured the running of the electromagnetic coupling constant (alpha) as a function of the energy. This important measurement has been obtained through the process of conversion of electron-positron pairs into muon-antimuon pairs.
The measurement, the first ever performed in the energy range 0.6-1.0 GeV, shows experimentally that the appearance in the vacuum of quark-antiquark pairs shields and modifies the electromagnetic interaction between charged particles. Therefore, a phenomenon predicted by the quantum field theory, has been confirmed by the KLOE-2 experiment.
The paper in press on Physics Letters B, is available in open access at the following link: https://arxiv.org/pdf/1609.06631.pdf
A more detailed description of the measurement is available here.