Fiducial polarization observables in hadronic WZ production: a next-to-leading order QCD+EW study

Julien Baglio,Le Duc Ninh

doi:10.1007/jhep04(2019)065

Abstract

We present a study at next-to-leading-order (NLO) of the process pp → W±Z → ℓνlℓ′+ℓ′−, where ℓ, ℓ′ = e, μ, at the Large Hadron Collider. We include the full NLO QCD corrections and the NLO electroweak (EW) corrections in the double-pole approximation. We define eight fiducial polarization coefficients directly constructed from the polar-azimuthal angular distribution of the decay leptons. These coefficients depend strongly on the kinematical cuts on the transverse momentum or rapidity of the individual leptons. Similarly, fiducial polarization fractions are also defined and they can be directly related to the fiducial coefficients. We perform a detailed analysis of the NLO QCD+EW fiducial polarization observables including theoretical uncertainties stemming from the scale variation and parton distribution function uncertainties, using the fiducial phase space defined by the ATLAS and CMS experiments. We provide results in the helicity coordinate system and in the Collins-Soper coordinate system, at a center-of-mass energy of 13 TeV. The EW corrections are found to be important in two of the angular coefficients related to the Z boson, irrespective of the kinematical cuts or the coordinate system. Meanwhile, those EW corrections are very small for the W± bosons.

Highlights

That W and Z bosons produced at hadron colliders are in principle polarized and that the angular distributions of the final-state leptons display an asymmetry that reflects the polarization of the underlying gauge bosons
We perform a detailed analysis of the NLO QCD+EW fiducial polarization observables including theoretical uncertainties stemming from the scale variation and parton distribution function uncertainties, using the fiducial phase space defined by the ATLAS and CMS experiments
We have presented in this paper an NLO analysis, including both QCD and EW corrections, of the fiducial angular coefficients and of the fiducial polarization fractions of the W ± and Z bosons in the process pp → eνμ+μ− at the 13 TeV LHC, using the fiducial phase space provided by the ATLAS and CMS experiments and in two different coordinate systems

Summary

Introduction

That W and Z bosons produced at hadron colliders are in principle polarized and that the angular distributions of the final-state leptons display an asymmetry that reflects the polarization of the underlying gauge bosons. Similar studies for Z boson polarization in Z + jets channel have been presented by CMS [5] and ATLAS [6]. For on-shell (OS) production, next-to-leading order (NLO) QCD corrections have been calculated in refs. [22, 23] and very recently full NLO EW corrections including off-shell effects for 3 ν final state have been calculated in ref. A more modern study of polarization of gauge bosons produced at the LHC via various channels including W Z has been performed in ref. To the best of our knowledge, no detailed study of NLO QCD and EW corrections on polarization observables in W Z production at a hadron collider has been performed

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Conclusion