The proton is not a monolithic ball. It is a seething cloud of quarks and gluons that constantly appear and vanish. Parton distribution functions help describe this picture: they show the probability of encountering a quark or gluon with a certain energy inside the proton. Previously, these functions were determined separately from other important numbers, such as the coupling strength of quarks or the mass of the heaviest elementary particle, the top quark.

Now, an international team of physicists has, for the first time, combined data from two legendary facilities. The electron-proton collider HERA in Hamburg provided precise snapshots of the proton through electron scattering. Proton-proton collisions at the Large Hadron Collider added information about the production of jets, W and Z bosons, and top-quark pairs. The analysis was performed with record theoretical precision — even subtle effects of quark motion inside the top quark and the emission of additional gluons were taken into account.

The result is the simultaneous extraction of the strong coupling, the top-quark mass, and the weak mixing angle (which governs weak decays). The precision matches the best world measurements, but the key point is that correlations between these parameters and the internal structure of the proton are now visible. The authors did not stop there; they also placed constraints on hypothetical deviations from the Standard Model, so-called SMEFT operators. If new particles exist, they must be either very heavy or interact very weakly.

Such a combined analysis is a dress rehearsal for the future. When new detectors come online and more data accumulate, scientists will be able to test the theory even more rigorously. Perhaps hidden in these correlations is the key to dark matter or the nature of mass.