DOI: 10.17182/hepdata.89875.v2/t2
title: "Table 2" of "Measurement of the $Z(\rightarrow\ell^+\ell^-)\gamma$ production cross-section in $pp$ collisions at $\sqrt{s} =13$ TeV with the ATLAS detector"

description: The measured fiducial cross section vs $E_{\mathrm{T}}^\gamma$. The central values are provided along with the statistical and systematic uncertainties together with the sign information. The statistical and "Uncor" uncertainty should be treated as uncorrelated bin-to-bin, while the rest are correlated between bins, and they are written as signed NP variations. 

The parton-to-particle correction factor $C_{theory}$ is the ratio of the cross-section predicted by Sherpa LO samples at particle level within the fiducial phase-space region defined in Table 4 to the predicted cross-section at parton level within the same fiducial region but with the smooth-cone isolation prescription defined above replacing the particle-level photon isolation criterion, and with Born-level leptons in place of dressed leptons. This correction should be applied on fixed order parton-level calculations. The systematic uncertainty is evaluated from a comparison with the correction factor obtained using events generated with Sherpa 2.2.2 at NLO. The uncertainty is defined as Max(stat error, systematic difference between Sherpa LO and Sherpa 2.2.2 NLO), and cannot be considered correlated bin-to-bin.

In the case that the calculations are valid for dressed leptons, a modified correction factor excluding the Born-to-dressed lepton correction should be applied instead. This correction only takes into account the particle-level isolation criteria, and is provided separately here.

The Sherpa 2.2.8 NLO cross-sections given below include a small contribution from EW $Z\gamma jj$ production.
description: CERN-LHC. 
Measurement of the $Z\gamma\rightarrow \ell^+ \ell^- \gamma$ production cross section in $pp$ collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector.

The production of a prompt photon in association with a Z boson is studied in proton--proton collisions at a centre-of-mass energy $\sqrt{s} =$~13 TeV. The analysis uses a data sample with an integrated luminosity of 139 fb$^{-1}$ collected by the ATLAS detector at the LHC from 2015 to 2018. The production cross-section for the process $pp\to\ell^{+}\ell^{-}\gamma+X$ ($\ell = e, \mu$) is measured within a fiducial phase space region defined by kinematic requirements on the photon and the leptons, and by isolation requirements on the photon. An experimental precision of 2.9% is obtained on the fiducial cross-section. Differential cross-sections are measured as a function of each of six kinematic variables characterising the $\ell^{+}\ell^{-}\gamma$ system. The data are compared to theoretical predictions based on next-to-leading-order and next-to-next-to-leading-order perturbative QCD calculations. The impact of next-to-leading-order electroweak corrections is also considered.

The fiducial region is defined as:
- opposite sign same flavour lepton pair (electron or muon)
- lepton $p_{\mathrm{T}}&gt;30, 25$ GeV, $|\eta|&lt;2.47$, dressed 
- photon $E_{\mathrm{T}}&gt;30$ GeV, $|\eta|&lt;2.37$. 
- $m_{\ell\ell}&gt;40$ GeV, $m_{\ell\ell}+m_{\ell\ell\gamma}&gt;182$ GeV 
- $\Delta R(\ell, \gamma)&gt;0.4$
- isolation energy (the scalar sum of $E_{\mathrm{T}}$ for all stable particles except neutrinos and muons within a cone of $\Delta R=0.2$) around photon must be less than 7% of the photon $E_{\mathrm{T}}$.