WZ production beyond NLO for high-pT observables

TL;DR

The paper addresses the need for higher-order QCD accuracy in WZ production by merging WZ@NLO and WZj@NLO with LoopSim to approximate NNLO contributions, focusing on high-p_T observables. The bar-nNLO results show substantial corrections (30–100%) in several distributions and can reduce scale uncertainties in some regions, highlighting the importance of NNLO-like effects for precise SM tests and BSM searches. The method preserves leptonic decays and all off-shell/finite-width effects, offering a practical path toward improved WZ background predictions at the LHC. The work provides a framework and code interface for combining NLO results to approximate NNLO in di-boson processes.

Abstract

We use the LoopSim and VBFNLO packages to investigate a merged sample of partonic events that is accurate at NLO in QCD simultaneously for the WZ and WZ+jet production processes. In certain regions of phase space such a procedure is expected to account for the dominant part of the NNLO QCD corrections to the WZ production process. For a number of commonly used experimental observables, we find that these corrections are substantial, in the 30-100% range, and in some cases their inclusion can reduce scale uncertainties by a factor of two. As in the underlying VBFNLO calculations, we include the leptonic decays of the vector bosons and all off-shell and finite-width effects.

Figures (4)

• Figure 1: Example diagram contributing to WZ production at LO, NLO and NNLO.
• Figure 2: Differential cross sections and K factors for the effective mass observable, defined in Eq. (\ref{['eq:HT']}), for the LHC at $\sqrt{s}=8\, \text{TeV}$. The bands correspond to varying $\mu_F=\mu_R$ by factors 1/2 and 2 around the central value from Eq. (\ref{['eq:ren']}). The cyan solid bands give the uncertainty related to the $R_\text{LS}$ parameter varied between 0.5 and 1.5. The distribution is a sum of contributions from two unlike flavor decay channels, $ee\mu\nu_\mu$ and $\mu\mu e\nu_e$.
• Figure 3: Differential cross sections and K factors for the $p_T$ of the hardest lepton for the LHC at $\sqrt{s}=8\, \text{TeV}$ (left) and $\sqrt{s}=14\, \text{TeV}$ (right). The bands correspond to varying $\mu_F=\mu_R$ by factors 1/2 and 2 around the central value from Eq. (\ref{['eq:ren']}). The cyan solid bands give the uncertainty related to the $R_\text{LS}$ parameter varied between 0.5 and 1.5. The distribution are sums of contributions from two unlike flavor decay channels, $ee\mu\nu_\mu$ and $\mu\mu e\nu_e$.
• Figure 4: Differential cross sections and K factors for the missing transverse energy (left) and the transverse mass of the WZ system (right) for the LHC at $\sqrt{s}=8\, \text{TeV}$. The bands correspond to varying $\mu_F=\mu_R$ by factors 1/2 and 2 around the central value from Eq. (\ref{['eq:ren']}). The cyan solid bands give the uncertainty related to the $R_\text{LS}$ parameter varied between 0.5 and 1.5. The distribution are sums of contributions from two unlike flavor decay channels, $ee\mu\nu_\mu$ and $\mu\mu e\nu_e$.