Prediction of pair production of Z bosons at LHC calculated with previously unattainable precision
07.08.2014
Researchers at the Physics Institutes of the University of Zurich and Johannes Gutenberg University Mainz (JGU) have succeeded in generating a particularly accurate model prediction for Z boson pair production, an important scattering process at the Large Hadron Collider (LHC) at CERN. For this purpose, the scientists had to develop innovative analytical methods based on state-of-the-art mathematical and computer algebra techniques. "Our methods make it possible to generate a variety of precise and detailed predictions for the currently much discussed pair production of Z and W bosons," explained Dr. Andreas von Manteuffel of the Institute of Physics at Mainz University. Such exact predictions are specifically required in order to discover effects during these processes that may be associated with the so-called 'New Physics,' a concept that extends beyond the Standard Model of physics. It is possible to describe almost all physical observations using the Standard Model of particle physics but there are lacunae. As a consequence, research is being conducted worldwide in order to explain these deficiencies and establish a 'New Physics.'
At the LHC, the world's largest accelerator ring operated by the European Organization for Nuclear Research CERN near Geneva, beams of protons traveling at tremendous speeds are collided and the particles that result from the collisions are carefully analyzed. The aim of these scattering experiments is to understand the fundamental constituents of matter and their interactions. The exchange particles associated with the weak nuclear force, the Z and W bosons, play an important role here. Pairs of these particles are created, for example, when the recently discovered Higgs boson decays.
Using a perturbation theory approach, it is possible to perform precise calculation of such processes using so-called 'loop diagrams' whereby, however, not only the accuracy, but also the difficulty of the calculation increases with the number of loops per diagram. In order to evaluate two-loop calculations, analytical methods and computer programs have been developed that make extensive use of symbolic algebra systems. The associated special mathematical functions, so-called multiple polylogarithms, are handled with the aid of new co-product algorithms. The scientists hope that, with the aid of a combination of these different types of techniques, they will be able to predict other scattering processes with a greater precision than was previously possible.
The work was undertaken in an international joint project involving the JGU Cluster of Excellence "Precision Physics, Fundamental Interactions and Structure of Matter" (PRISMA) and the working groups of Professor Thomas Gehrmann, Professor Stefano Pozzorini, and Dr. Massimiliano Grazzini of the University of Zurich.