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Register a new userNLO QCD and electroweak corrections to $Z+gamma$ production with leptonic Z-boson decays
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The next-to-leading-order electroweak corrections to $ppto l^+l^-/bar u u+gamma+X$ 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 Frixiones 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 $ZZgamma$ and $Zgammagamma$ couplings.
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This article presents results for the last unknown two-loop contributions to the $Z$-boson partial widths and $Z$-peak cross-section. These are the so-called bosonic electroweak two-loop corrections, where bosonic refers to diagrams without closed fermion loops. Together with the corresponding results for the $Z$-pole asymmetries $A_l, A_b$, which have been presented earlier, this completes the theoretical description of $Z$-boson precision observables at full two-loop precision within the Standard Model. The calculation has been achieved through a combination of different methods: (a) numerical integration of Mellin-Barnes representations with contour rotations and contour shifts to improve convergence; (b) sector decomposition with numerical integration over Feynman parameters; (c) dispersion relations for sub-loop insertions. Numerical results are presented in the form of simple parameterization formulae for the total width, $Gamma_{rm Z}$, partial decay widths $Gamma_{e,mu},Gamma_{tau},Gamma_{ u},Gamma_{u},Gamma_{c},Gamma_{d,s},Gamma_{b}$, branching ratios $R_l,R_c,R_b$ and the hadronic peak cross-section, $sigma_{rm had}^0$. Theoretical intrinsic uncertainties from missing higher orders are also discussed.
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