Background: Interest in the behavior of nucleon electromagnetic form factors at large momentum transfers has steadily increased since the discovery, using polarization observables, of the rapid decrease of the ratio $G_E^p/G_M^p$ of the proton's electric and magnetic form factors for momentum transfers $Q^2\gtrsim 1$ ${\mathrm{GeV}}^2$, in strong disagreement with previous extractions of this ratio using the traditional Rosenbluth separation technique.

Testing the chiral anomaly: Pi mesons, also known as pions, consist of a quark and an antiquark and are extremely unstable. Neutral pions have a lifetime of only ∼80 attoseconds, decaying into two photons. Quantum chromodynamics (QCD), the theory of quarks and gluons, predicts this decay and the associated lifetime using the mechanism of broken chiral symmetry—the so-called chiral anomaly. Measuring the lifetime to high precision then provides a benchmark for theories that aim to improve on this original prediction. Larin et al. measured this lifetime with an uncertainty that was half that of the previous most precise result (see the Perspective by Meyer). The measured value was consistent with the original QCD prediction and less consistent with other theoretical approaches. Science , this issue p. 506 ; see also p. 469

Background: Extracting the proton charge radius from electron scattering data requires determining the slope of the charge form factor at $Q^2$ of zero. As experimental data cannot reach that limit, numerous methods for making the extraction have been proposed.