1. Lee Pondrom University of Wisconsin
Pythia status 8 Feb 2010
Lee Pondrom
University of Wisconsin

2. 2->2 Pythia compared to nlojet++ born and jet_chi program

3. Normalization
Each set of four mass plots has one overall normalization.
All programs agree on the mass dependence of the cross section.
Nlojet++ born agrees better with Pythia as the mass increases.

4. The earlier plot

5. Discrepancy at low 
Fixed by symmetrizing the cross sections for non-identical partons in the final state because the jets are indistinguishable.
The cross sections are symmetrized ut.
Explained in Barger and Phillips p 305.

6. conclusion
We understand Pythia. It agrees well with the data, and strengthens the Pythia based quark substructure analysis.
Further analysis using nlojet++, which is not understood, is problematic.