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• MATRIX ELEMENT

• Explicitly calculate Feynman Diagrams order by order

• This is in principle the correct way to do it since takes into

• account exact kinematics, full interference and

• helicity structure

• but: Calculations become increasingly difficult in higher orders

• 2 ® 2, 2 ® 3, 2 ® 4 Born term

• 2 ® 2 up to 1 loop correction for parton interactions

• in e+e- complete 2o order corrections exist

• need to include higher orders to explain for instance 4 jet events

• as CALCULATION IS ONLY DONE IN THIS WAY