QCD anatomy of photon isolation

Abstract

To separate the energetic photons produced in hard scattering processes from those from other sources, measurements impose isolation requirements which restrict the hadronic radiation inside a cone around the photon. In this paper, we perform a detailed factorization analysis of the QCD effects associated with photon isolation. We show that for small cone radius $R$, photon isolation effects can be captured by a fragmentation function describing the decay of a parton into a photon accompanied by hadronic radiation. We compute this fragmentation function for different isolation criteria and solve the associated renormalization group equations to resum logarithms of $R$. For small isolation energy, the cone fragmentation function factorizes further, into collinear functions describing energetic quarks and gluons near the cone boundary and functions encoding their soft radiation emitted into the cone. Based on this factorization we also resum the non-global logarithms of the ratio of the photon energy and the isolation energy, so that we control all logarithmically enhanced terms in the cross section. Finally, we provide a simple formula to convert NNLO cross section results from smooth-cone isolation to fixed-cone isolation.

38 pages, 13 figures. v2: journal version, corrected (A.2)

References in corpus (12)

• The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations
• Triphoton production at hadron colliders in NNLO QCD
• NNLO QCD corrections to three-photon production at the LHC
• NNLO QCD corrections to diphoton production with an additional jet at the LHC
• Threshold and jet radius joint resummation for single-inclusive jet production
• Next-to-leading order QCD corrections to diphoton-plus-jet production through gluon fusion at the LHC
• Jet Shape Resummation Using Soft-Collinear Effective Theory
• Higher-order non-global logarithms from jet calculus
• Scale and isolation sensitivity of diphoton distributions at the LHC
• Photon Fragmentation in the Antenna Subtraction Formalism
• Two-loop anomalous dimension for the resummation of non-global observables
• The Jet Shape at NLL${}^{\prime }$

Cited by in corpus (4)

• Isolated photon production in association with a jet pair through next-to-next-to-leading order in QCD
• Resummation of Next-to-Leading Non-Global Logarithms at the LHC
• NLO QCD predictions for $\mathbf{t}\bar{\mathbf{t}}\mathbf{\gamma }$ with realistic photon isolation
• Stable perturbative predictions for isolated photon production with a jet pair at large $m_{j_1{j}_2}$