Isolating Prompt Photons with Narrow Cones

TL;DR

This paper improves the theoretical understanding of isolating prompt photons in hadronic collisions by resumming large logarithmic terms associated with narrow isolation cones, enhancing the accuracy of cross section calculations.

Contribution

It introduces a resummation method for leading logarithmic terms related to small cone sizes, addressing perturbative violations of unitarity in NLO calculations.

Findings

Resummation stabilizes cross section predictions for small cones.

Large logarithmic terms significantly affect the fragmentation scale dependence.

Implications for experimental isolation criteria are discussed.

Abstract

We discuss the isolation of prompt photons in hadronic collisions by means of narrow isolation cones and the QCD computation of the corresponding cross sections. We reconsider the occurence of large perturbative terms with logarithmic dependence on the cone size and their impact on the fragmentation scale dependence. We cure the apparent perturbative violation of unitarity for small cone sizes, which had been noticed earlier in next-to-leading-order (NLO) calculations, by resumming the leading logarithmic dependence on the cone size. We discuss possible implications regarding the implementation of some hollow cone variants of the cone criterion, which simulate the experimental difficulty to impose isolation inside the region filled by the electromagnetic shower that develops in the calorimeter.