QCD Physics at the Tevatron Page: 2 of 14
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1 Introduction
Measurements aimed to test the predictions of Quantum Chromodynamics
(QCD), the currently accepted theory of the strong interactions among quarks
and gluons, represent a very important part of the physics program carried out
at the Tevatron pp Collider. The large amount of data expected to be accumu-
lated during Run II and the increase in center-of-mass energy (-F) from 1.8
to 1.96 TeV, give CDF 1) and D9 2) experiments an unique opportunity to
make precision tests of next-to-leading order perturbative QCD (NLO pQCD)
and, by looking for deviations from theory, to search for new particles and new
interactions down to a distance scale of ~ 10-19 m.
An optimal understanding of QCD in hadron collisions allows to improve
the constraints on the fundamental parameters of the theory, a, and the parton
distribution functions (PDFs); results in a better control on the standard QCD
production which represents the main background for most of the processes
of interest, such as top and Higgs production; gives phenomenological input
for the modeling of the non-perturbative regime (where the theory fails in its
predictivity), such as the "soft" interactions generating the underlying event
which accompanies the "hard" collision.
2 Inclusive Jet Cross Section
2.1 Experience from Run I
During Run I, the CDF and D9 Collaborations performed several QCD mea-
surements which, in general, were found to be in reasonable agreement with
theoretical expectations. However, initial inclusive jet cross section measure-
ments showed an excess of data at high ETA over NLO pQCD predictions,
which raised great interest among the high energy physics community and
stimulated a reevaluation of the uncertainties associated to theoretical calcu-
lations 3). Subsequent studies have demonstrated that such excess can be
explained within the Standard Model in terms of a larger than expected gluon
distribution at high x. A better agreement of data versus theory was actually
observed in subsequent measurements involving an increased data sample when
PDFs with an enhanced gluon contribution at high x (CTEQ4HJ) were consid-
ered 4, 5) (see fig.1, left). Given the large uncertainty in the NLO calculations
arising from the flexibility allowed by current knowledge of PDFs as well as the
uncertainty in the experimental results, CDF and D9 data were found to be
consistent between them, with previous measurements and with NLO pQCD.
Most recent global PDFs fits have used results from these Run I analyses
so to include the Tevatron high ET jet data in the determination of the high
x gluon distribution. In particular, by involving jets in a range of rapidity
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Latino, G. QCD Physics at the Tevatron, article, June 8, 2004; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc784929/m1/2/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.