A study of event shape observables in proton-antiproton
collisions at s**(1/2) ñ.96 TeV is presented. The data for this
analysis were recorded by the CDF II detector at the Tevatron collider.
The variables studied are the transverse thrust and thrust minor,
both defined in the plane perpendicular to the beam direction. The
observables are measured using energies from unclustered calorimeter
cells. In addition to studies of the differential distributions, we
present the dependence of event shape mean values on the leading jet
transverse energy. Data are compared with PYTHIA Tune A and to resumed
parton level predictions that were matched to fixed order results at NLO
accuracy (NLO+NLL). Predictions from PYTHIA Tune A agree fairly well
with the data. However, the underlying event contributes significantly
to those observables, making it difficult to make direct comparisons to
the NLO+NLL predictions, which do not account for the underlying event.
To overcome this difficulty, we introduce a new observable, a weighted
difference of the mean values of the thrust and thrust minor, which
is less sensitive to the underlying event, allowing for a comparison
with NLO+NLL. Both PYTHIA Tune A and the NLO+NLL calculations agree well
within the 20% theoretical uncertainty with the data for this observable,
indicating that perturbative QCD successfully describes shapes of the
hadronic final states.
Return to top of page.
Go to Physics Results
Updated: Thursday, 2011 August 04 11:01:46 CDT automatically from input from "Carol Picciolo"