Ratio of the Isolated Photon Cross Sections at \sqrt{s} = 630 and 1800 GeV

Abstract

The inclusive cross section for production of isolated photons has been measured in \pbarp collisions at $\sqrt{s} = 630$ GeV with the \D0 detector at the Fermilab Tevatron Collider. The photons span a transverse energy ($E_T$) range from 7-49 GeV and have pseudorapidity $|η| < 2.5$. This measurement is combined with to previous \D0 result at $\sqrt{s} = 1800$ GeV to form a ratio of the cross sections. Comparison of next-to-leading order QCD with the measured cross section at 630 GeV and ratio of cross sections show satisfactory agreement in most of the $E_T$ range.

Figures (5)

• Figure 1: Distribution of the discriminant, $f$, for determining photon purity, where $E_1$ is in units of GeV. Points with error bars indicate data. Broken lines indicate simulated distributions of (a) single photons, and jet background (b) without and (c) with charged tracks. The solid line depicts a fit sum of all three distributions.
• Figure 2: The photon purity as a function of $E_{T}^{\gamma}$ for central and forward photons. The error bars indicate the uncertainty in the fit purity and are larger than errors derived from statistical analysis alone.
• Figure 3: The cross section for production of isolated photons in central and forward regions at $\sqrt{s}=630$ GeV. The error bars show the total uncorrelated error, and the curves show cross sections predicted from NLO QCD.
• Figure 4: Comparison of the measured cross section for production of isolated photons at $\sqrt{s}=630$ GeV with NLO QCD using CTEQ5M parton distribution functions. The error bars indicate the uncorrelated uncertainty and the shaded bands indicate the correlated uncertainty
• Figure 5: The ratio of the dimensionless cross sections, $\sigma_D(\sqrt{s}=630{\rm{~GeV}})/\sigma_D(\sqrt{s}=1800{\rm{~GeV}})$. The error bars indicate the uncorrelated uncertainty and the shaded bands indicate the correlated uncertainty.