Multiple photon corrections to the neutral-current Drell-Yan process

TL;DR

The paper develops and validates a method to include higher-order final-state QED corrections from multi-photon radiation in neutral-current Drell-Yan processes using the HORACE Monte Carlo. By solving a QED parton shower for lepton structure functions and comparing with fixed-order benchmarks like ZGRAD2, it quantifies the impact on key observables for W mass calibration, finding small total cross-section shifts but non-negligible distortions in differential distributions near the Z peak. The results inform precision EW studies at the Tevatron Run II and LHC, highlighting detector-dependent Z-mass shifts and the need to account for multiple photon radiation in analyses. The work also outlines future enhancements, including comparisons with PHOTOS and combining EW and QCD radiation in a single framework.

Abstract

Precision studies of single W and Z production processes at hadron colliders require progress in the calculation of electroweak radiative corrections. To this end, higher-order QED corrections to the neutral-current Drell-Yan process, due to multiple photon radiation in Z leptonic decays, are calculated. Particular attention is paid to the effects induced by such corrections on the experimental observables which are relevant for high-precision measurements of the W-boson mass at the Tevatron Run II and the LHC. The calculation is implemented in the Monte Carlo event generator HORACE, which is available for data analysis.

Figures (4)

• Figure 1: The invariant mass distribution $M_{l^+ l^-}$ (left panel) and relative effect of ${\mathcal{O}}(\alpha)$ (right panel, up) and higher-order QED corrections (right panel, down) for the $Z$ lepton decays $Z \to e^+ e^-, \mu^+ \mu^-$ at $\sqrt{s} = 2$ TeV, according to the lepton identification criteria discussed in the text.
• Figure 2: The $Z$ transverse mass distribution $M_{T}^Z$ (left panel) and relative effect of ${\mathcal{O}}(\alpha)$ (right panel, up) and higher-order QED corrections (right panel, down) for the $Z$ lepton decays $Z \to e^+ e^-, \mu^+ \mu^-$ at $\sqrt{s} = 2$ TeV, according to the lepton identification criteria discussed in the text.
• Figure 3: The $Z$ rapidity distribution (left panel) and effect of ${\mathcal{O}}(\alpha)$ (right panel, up) and higher-order QED corrections (right panel, down) for the $Z$ lepton decays $Z \to e^+ e^-, \mu^+ \mu^-$ at $\sqrt{s} = 2$ TeV, according to the lepton identification criteria discussed in the text.
• Figure 4: The forward-backward asymmetry $A_{FB}$ (left panel) and effect of ${\mathcal{O}}(\alpha)$ (right panel, up) and higher-order QED corrections (right panel, down) for the $Z$ lepton decays $Z \to e^+ e^-, \mu^+ \mu^-$ at $\sqrt{s} = 2$ TeV, according to the lepton identification criteria discussed in the text.