arXiv : Isolated photon and photon+jet production at NNLO QCD accuracy

Chen, Xuan; Huss, Alexander; Glover, Nigel; Gehrmann, Thomas; Höfer, Marius

doi:10.1007/JHEP04(2020)166

Article
Report number	arXiv:1904.01044 ; IPPP-19-23 ; ZU-TH-13-19 ; IPPP/19/23 ; ZU-TH 13/19 ; CERN-TH-2019-034
Title	Isolated photon and photon+jet production at NNLO QCD accuracy
Author(s)	Chen, Xuan (Zurich U.) ; Gehrmann, Thomas (Zurich U.) ; Glover, Nigel (Durham U., IPPP) ; Höfer, Marius (Zurich U.) ; Huss, Alexander (CERN)
Publication	2020-04-24
Imprint	2019-04-01
Number of pages	30
Note	Submitted to J.High Energy Phys. Submitted to J.High Energy Phys. JHEP version, 30 pages, 17 figures
In:	JHEP 2020 (2020) 166
DOI	10.1007/JHEP04(2020)166 (publication)
Subject category	hep-ph ; Particle Physics - Phenomenology
Abstract	We describe the calculation of the next-to-next-to-leading order (NNLO) QCD corrections to isolated photon and photon-plus-jet production, and discuss how the experimental hadron-level photon definition and isolation criteria can be approximated in the theoretical parton-level calculation. The NNLO corrections lead to a considerable reduction of the theory uncertainty on the predictions, typically to less than five per cent, and enable an improved description of experimental measurements from ATLAS and CMS.
Copyright/License	publication: © 2020-2024 The Authors (License: CC-BY-4.0) preprint: (License: arXiv nonexclusive-distrib 1.0)

$Distribution in $\left|\cos\theta^*\right|$ at LO, NLO and NNLO. The predictions are compared to ATLAS data~\protect{\cite{Aaboud:2017kff}}.$ $Total cross section for different parameter choices ($\varepsilon_d=0.05,0.1,0.15$, $n=\frac{1}{2},1,2$) for both dynamical photon isolation (\dynIso)~\protect{\cite{Frixione:1998jh}} (dark colours) and the dynamical cone part of the hybrid photon isolation (\hybIso) (light colours). The default cone size for \dynIso is $R_d=0.4$, while for \hybIso it is $R_d=0.1$. For the specific parameter choice $\varepsilon_d=0.1, n=2$ we also investigate variations of the cone size by factors $\frac{1}{2}$ and $2$. The fixed cone parameters of the hybrid isolation are chosen according to the ATLAS measurement~\protect{\cite{Aaboud:2017kff}}. The \fixIso~prediction (using JETPHOX~\cite{Catani:2002ny}) and the ATLAS measurement are shown for comparison.$ $Dependence of the total cross section for photon + jet production (ATLAS 13~TeV measurement~\protect\cite{Aaboud:2017kff}) at NLO and NNLO on the conesize $R_d$ of the inner dynamical cone used in the hybrid isolation procedure. All other isolation parameters are fixed: $\varepsilon_d=0.1$, $n=2$, $R=0.4$, $E_T^\mathrm{thres}=10~\GeV$, $\varepsilon=0.0042$. The line is a fit of a function with form $f(R_d)=a\cdot\log(1/R_d)+b$ to the NLO prediction at the central scale. The NLO prediction for fixed cone isolation is obtained with the BFG parametrization~\protect\cite{Bourhis:1997yu} of the photon fragmentation functions, and computed with the JETPHOX code~\protect\cite{Catani:2002ny}. Its uncertainty band contains only variations of the factorization and renormalization scales, while the small fragmentation scale uncertainty is superimposed on the central and extremal values. The LO prediction is independent on the isolation procedue.$ Show more plots

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