Run 9 Zero Jet Mass Dijets at Parton Level: Effect on Asymmetry

Look at how using the massless dijet mass formula at the parton level (described here for the cross section) affects various aspects of the asymmetry measurement ...

Figure 1: Parton level mass shifts (parton level mass - detector level mass) for the full mass formula (solid points) and the massless formula (open points). Red points are no track inefficiency, blue points are 4% track inefficiency, and green points are 7% track inefficiency.

As can be seen, the change in the mass shifts used (red points) are between 300 and 500MeV.

Figure 2: Comparison of the delta_ALLs (detector level ALL - parton level ALL) for the full mass formula (solid points) and massless formula (open points). Red points are for DSSV, blue points are for DSSV2009a, and green points are for LSS2010pos.

There is a correction and a systematic associated with the trigger and reconstruction bias. The correction is taken as half of the sum of the lowest and highest delta_ALL values and the systematic is half the difference between the lowest and highest delta_ALL. It appears that the size of the correction will increase slightly (mainly at larger masses) and the systematic will stay roughly the same.

Figure 3: Comparison of the parton level PYTHIA/NLO cross section ratios using the full mass and massless formulas for the PYTHIA dijet mass.

The PYTHIA-NLO systematic is taken as the shift needed to bring the PYTHIA cross section to the NLO cross section at a given mass value. The systematic from the full mass PYTHIA cross section ranges between roughly 0.25 and 2 GeV. As the massless PYTHIA parton level cross section is closer to the NLO cross section, this systematic should decrease.