We can measure _s by using WIRED to determine the ratio of Z-decays into two and three jets. The strong coupling constant is then calculated with the equation

_s = k N_3-jets/N_2-jets

where N_2-jets and N_3-jets is the number of events with two and three jets respectively, and k is a constant that depends on the computer program used to group the particles into jets. This jet creation procedure depends on the parameter d (or d_join).

The diagram to the left gives the relation between k and d. For the events used in WIRED we have d = 5 GeV/c.

Now you can determine _s yourself by counting the number events with two and three jets and then using the equation above. If you already have completed the previous task (calculation of the branching ratios of the Z particle), you can use the number of events with two and three jets you had there. Use the diagram to the left to determine k.

Compare your result with the theoretical value from the Standard Model, see the link below.