DOI: 10.17182/hepdata.89875.v1/t4
title: "Table 4" 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 $m(\ell\ell\gamma)$. 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.

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 $E_{\mathrm{T}}$.