The goal with the second exercise is to measure the strength of the strong interaction. All four forces of nature are characterised by a coupling constant that determines the strength of the force. Gravity is the weakest force. Its coupling constant is the usual constant of gravity, G.

The coupling constants of the electromagnetic force and the strong force are called and _s respectively. These coupling constants determine the strength of different processes and are some of the most fundamental parameters in nature.

When a Z particle decays into two quarks there is a certain probability that one of the quarks emits a gluon. This probability is proportional to the coupling constant of the strong force, _s. By counting how often a gluon is created we can measure the coupling constant of the strong force.