Next-to-Leading Order Calculations

Calculations to next-to-leading order are expected to provide more reliable estimates of the total rates as they account for the presence of hard parton emissions. Furthermore, next-to-leading order calculations are necessary for the determination of fundamental parameters such as $\alpha_S$ and the parton density distributions. At next-to-leading order, the different diagrams produce both positive and negative contributions to the cross section. The negative contributions make it difficult to implement next-to-leading order calculations in full hadron level Monte Carlo event generators.