Comparison of the Isolated Direct Photon Cross Sections in $p\bar{p}$ Collisions at $\sqrt{s}=1.8$ TeV and $\sqrt{s}=0.63$ TeV

Abstract

We have measured the cross sections $d^2\sigma /d{P}_{T}d\eta$ for production of isolated direct photons in \pbarp collisions at two different center-of-mass energies, 1.8 TeV and 0.63 TeV, using the Collider Detector at Fermilab (CDF). The normalization of both data sets agree with the predictions of Quantum Chromodynamics (QCD) for photon transverse momentum ($P_T$) of 25 GeV/c, but the shapes versus photon $P_T$ do not. These shape differences lead to a significant disagreement in the ratio of cross sections in the scaling variable $x_T(\equiv 2P_T/\sqrt{s}$). This disagreement in the $x_T$ ratio is difficult to explain with conventional theoretical uncertainties such as scale dependence and parton distribution parameterizations.

34 pages, submitted to Physical Review D

References in corpus (5)

• Global QCD Analysis of Parton Structure of the Nucleon: CTEQ5 Parton Distributions
• Higher-Order QCD Corrections in Prompt Photon Production
• The Isolated Photon Cross Section in p pbar Collisions at sqrt(s) = 1.8 TeV
• Ratio of the Isolated Photon Cross Sections at \sqrt{s} = 630 and 1800 GeV
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