Jet Multiplicity versus Multijet Mass
Within the framework of perturbative QCD, events with more than two
jets arise from higher order corrections to the leading order 2 -> 2
scattering process. Hence, the rate at which events with three,
four, five, ... jets are observed provides a test of the higher
order QCD corrections. CDF has measured the ratio of N-jet / 2-jet
rates as a function of multijet mass for N = 3, 4, 5, and 6. These ratios
do not vary much with mass and are well described by both parton shower
Monte Carlo predictions and by 2 -> N matrix element predictions.
Jet multiplicity Figure
Figure caption: Jet multiplicity ratios shown as a function of
multijet mass. The ratio of the exclusive N-jet / 2-jet rates are
shown with a minimum jet transverse energy requirement of 20 GeV.
The CDF data
(solid points) are compared with HERWIG predictions (triangles)
and NJETS predictions (bands) for events with total-transverse-energy
exceeding 420 GeV and leading-jet angle satisfying cos theta < 0.67.
The inner bands show the variation of the NJETS predictions with choice
of structure function. The outer bands show the variations with choice
of Q^2 scale.
More information can be found in
prl 75, 608 (1995)