Abstract
The next-to-leading-order electroweak corrections to $pp\to l^+l^-/\bar\nu\nu+\gamma+X$ production, including all off-shell effects of intermediate Z bosons in the complex-mass scheme, are calculated for LHC energies, revealing the typically expected large corrections of tens of percent in the TeV range. Contributions from quark-photon and photon-photon initial states are taken into account as well, but their impact is found to be moderate or small. Moreover, the known next-to-leading-order QCD corrections are reproduced. In order to separate hard photons from jets, both a quark-to-photon fragmentation function \'a la Glover/Morgan and Frixione's cone isolation are employed. The calculation is available in the form of Monte Carlo programs allowing for the evaluation of arbitrary differential cross sections. Predictions for integrated cross sections are presented for the LHC at 7 TeV, 8 TeV, and 14 TeV, and differential distributions are discussed at 14 TeV for bare muons and dressed leptons. Finally, we consider the impact of anomalous $ZZ\gamma$ and $Z\gamma\gamma$ couplings.
Highlights
A strong sensitivity to potentially existing photon-Z-boson couplings (ZZγ, Zγγ) which are absent in the SM as elementary interactions, so that non-standard ZZγ and Zγγ couplings can be constrained by investigating Z + γ final states
A Monte Carlo program for Z + γ production at NLO QCD was presented in ref. [23] using amplitudes from ref. [24], where the leptonic decays of the W/Z bosons are treated in the narrow-width approximation, while the spin information is retained via decay-angle correlations
Jet veto allowing a maximal jet transverse momentum of 100 GeV does not diminish the QCD corrections considerably, since energy scales dominating the integrated cross section are much lower for our setup, which allows for photons down to transversemomentum values of 15 (25) GeV
Summary
The production of a leptonically decaying Z boson in association with a hard photon includes two different final states. Owing to the two photons in the initial state the partonic cross section is convoluted two times with the very small photon PDFs, so that the contribution to the pp cross section is expected to be small. For this reason we give results for its contribution separately and do not consider NLO EW corrections to this LO process. Since this process only contains charged leptons as intermediate particles there are no QCD corrections at NLO. Replacing σNLO QCD by σNNLO QCD, as worked out in ref. [26], would deliver state-of-the-art predictions based on fixed perturbative orders
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