DESY congratulates this Year’s Nobel Laureates, David Gross, David Politzer and Frank Wilczek

“The DESY physics community congratulates the winners of this year’s Nobel Prize, David Gross, David Politzer and Frank Wilczek, on their award”, said Robert Klanner, Research Director at DESY.“ The Nobel Prize recognizes a pioneering discovery on the way towards the comprehensive theory of the strong force. This is particularly gratifying for DESY, since scientists at the Laboratory’s accelerators PETRA and HERA were not only able to experimentally confirm the predictions made by Gross, Politzer and Wilczek, they also discovered unexpected new properties of the strong force,” he adds.
Indeed, Frank Wilczek begins his internet list of “selected publications, with brief comments” with the three papers on the theory of the strong force that were published in 1973 and 1974. One comment reads: “... The most dramatic of these [tests], that protons viewed at ever higher resolution would appear more and more as field energy (soft glue), was only clearly verified at HERA twenty years later”.

Innenleben des Protons

Fig. 1
The inside of the proton when seen with the sharp eyes of HERA – a “dense soup” of quarks and gluons.

The discovery of “asymptotic freedom in the theory of the strong interaction”, which now won the Nobel Prize, is crucial to our understanding of the force which binds together the quarks in the protons and neutrons, and the protons and neutrons inside the atomic nucleus. Gross, Politzer and Wilczek found that this force, described by quantum chromodynamics (QCD), becomes weaker and weaker at smaller and smaller distances, or at higher and higher energies. They could thus explain why quarks in the proton behave as nearly free particles at high energies, and predicted that protons, when studied at the smallest distances, would look like a “dense soup” of quarks, anti-quarks and gluons, the particles which are responsible for the strong force.
The study of QCD is one of the main points of the particle physics programme at the DESY research centre in Hamburg, with its accelerator facilities PETRA (1978-1984, electron-positron collisions) and HERA (since 1992, electron/positron-proton collisions). Experiments here have tested and confirmed in a unique way many of the predictions of the theory. Three outstanding examples are: In 1979 the gluon was discovered at the PETRA storage ring. With the commissioning of the “super electron microscope” HERA, physicists had a facility at their disposal which for the first time allowed them to see deep enough inside the proton to find the “dense quark soup” predicted by the Nobel laureates. And at HERA, they were able to precisely measure how the strong force becomes weaker and weaker at high energies.

Plot für Experten

Fig. 2
The plot for the experts shows the experimental evidence for the “asymptotic freedom in the theory of the strong interaction” – i.e. for the discovery which has been honoured by this year’s Nobel Prize in Physics. The plot displays results from the HERA experiments H1 and ZEUS which directly confirm the “asymptotic freedom”: The strength of the strong force (described by the strong coupling constant alpha-S) decreases with increasing energy scale.

The theory of the strong force is extremely beautiful – it looks deceptively simple, but it is an incredibly rich theory which predicts many complex phenomena. Even after more than 30 years of intensive work, particle physicists are far from understanding the strong force completely, and studies at HERA continue to reveal many new and surprising puzzles. This year’s Nobel Prize in Physics acknowledges the importance of the study of the strong force – the most complex of the fundamental forces.