Comparison of the isolated direct photon cross sections in pp? collisions at ??s = 1.8 TeV and ??s = 0.63 TeV
Journal
Physical Review D
Journal Volume
65
Journal Issue
11
Date Issued
2002
Author(s)
Acosta, D. et al.
Abstract
We have measured the cross sections d2σ/d P Tdη) for production of isolated direct photons in pp̄ collisions at two different center-of-mass energies, 1.8 TeV and 0.63 TeV, using the Collider Detector at Fermilab. The normalization of both data sets agrees with the predictions of quantum chromodynamics for a photon transverse momentum (PT) of 25 GeV/c, but the shapes versus photon PT do not. These shape differences lead to a significant disagreement in the ratio of cross sections in the scaling variable xT(≡ 2PT/√s). This disagreement in the xT ratio is difficult to explain with conventional theoretical uncertainties such as scale dependence and parton distribution parametrizations. © 2002 The American Physical Society.
Type
journal article