Shedding new light on strong interactions

Collisions of highly energetic hadrons provide a wealth of information in nuclear and particle physics. Beyond shedding further insight into the nucleon and nuclei inner structures, they allow studying strong interactions between quarks and gluons. The field theory describing the interactions of such elementary particles — making up hadrons such as the proton, neutron and pion — is quantum chromodynamics (QCD). High-energy hadron collisions also serve as invaluable tools in the search for particle physics beyond the Standard Model.

The primary goal of the EU-funded project 'Resummation of higher orders in QCD perturbation theory' (RESUQCD) was to further develop all-order QCD resummation techniques for specific observables, thereby providing state-of-the-art theoretical predictions. In particular, RESUQCD investigated the resummation of logarithmic corrections of hard scattering cross-sections in perturbative QCD.

Project findings should lead to a better control of the theoretical predictions for many cross-sections in high-energy physics, ranging from fixed-target experiments to high-energy colliders. Project work will prove important for ongoing experiments in high-energy and particle physics throughout the world, such as COMPASS (Geneva, Switzerland), HERMES (Hamburg, Germany) and RHIC (Brookhaven, United States). Their primary goal is to provide new information on the nucleon inner structure. This can only be achieved by comparing data with theoretical predictions regarding the relevant kinematics of each experiment.

In COMPASS and HERMES, scientists have been using spin asymmetries in the photon–-gluon fusion process to explore the spin-dependent gluon distribution in the nucleon. In both fixed-target experiments, QCD threshold resummation effects are significant. RESUQCD derived the resummation of threshold logarithms at all orders for the gamma photo-production process with high transverse momentum.

RESUQCD studied various pure QCD reactions, mainly focusing on their phenomenology. In particular, scientists investigated jet production at the Large Hadron Collider (LHC), where resummation calculations may be used to predict the size of higher-order terms in the perturbative series. Other achievements include analysing helicity parton distributions and determining angular dependences of various transverse momentum distributions at the LHC that provide unique insights into gluon dynamics.

RESUQCD resummation studies provided new insights into the perturbative QCD structure at high orders, thereby enhancing understanding of strong interactions.