Inclusive Photon Production in Hadronic Collisions

TL;DR

This paper compares inclusive photon production data with NLO QCD calculations, examining the dependence on structure functions and scales, and provides a precise determination of the strong coupling constant alpha_s.

Contribution

It analyzes the compatibility of data with NLO QCD predictions, clarifies the role of structure functions and scales, and accurately determines alpha_s from collider data.

Findings

Data cannot be fitted with a single set of structure functions and scales.

Within the reliable xT range, no additional primordial kT dependence is needed.

Precise alpha_s value obtained from high-statistics collider data.

Abstract

High statistics fixed target and ISR inclusive photon production data are compared to next-to-leading order (NLO) QCD calculations. The dependence of the theoretical predictions on the structure functions, and on the theoretical scales is investigated. It is shown that the data cannot be simultaneously fitted with a single set of structure functions and scales. However, it is argued that as long as one restricts the data/theory comparison to the xT range where the theory is reliable, i.e. stable with respect to the scale variation, there is no need to introduce an additional primordial kT dependence except for Be data. Finally a precise determination of the strong coupling constant, alpha_s, is performed from the direct photon production cross sections obtained in high statistics pbar p and pp collisions at the CERN SPS (UA6) by a NLO QCD analysis.