Simulating W/Z+jets production at the CERN LHC

TL;DR

The paper validates SHERPA's merging of tree-level matrix elements with parton showers for W/Z plus jets production at the LHC, demonstrating robustness to merging parameters and good agreement with NLO shapes. It systematically compares SHERPA to fixed-order NLO calculations (MCFM) and to MC@NLO and PYTHIA, highlighting SHERPA's enhanced description of hard QCD radiation via multi-jet matrix elements. The results show SHERPA can reproduce key differential distributions and jet-topology features at LHC energies, though total rates remain at LO and may require K-factors. The work establishes SHERPA as a versatile tool for simulating high-multiplicity final states relevant for precision backgrounds and new-physics searches at the LHC.

Abstract

The merging procedure of tree-level matrix elements and the subsequent parton shower as implemented in the new event generator SHERPA will be validated for the example of single gauge boson production at the LHC. The validation includes consistency checks and comparisons to results obtained from other event generators. In particular, comparisons with full next-to-leading order QCD calculations prove SHERPA's ability to correctly account for additional hard QCD radiation present in these processes.

Figures (17)

• Figure 1: $p_\perp(Z)$ (upper row) and $p_\perp(e^-)$ (lower row) for $Q_{\rm cut}=15$ GeV, $50$ GeV and $100$ GeV (from left to right). The dashed reference spectrum has been obtained after averaging the results for $Q_{\rm cut}=15,\,20,\,30,\,50,\,100$ GeV.
• Figure 2: $\eta(Z)$ (upper row) and $\eta(e^-)$ (lower row) for $Q_{\rm cut}=15$ GeV, $50$ GeV and $100$ GeV (from left to right). The dashed reference spectrum has been obtained after averaging the results for $Q_{\rm cut}=15,\,20,\,30,\,50,\,100$ GeV.
• Figure 3: $p_\perp(Z)$ (upper row) and $\eta(Z)$ (lower row) for $Q_{\rm cut}=15$ GeV and different maximal numbers (2-4, from left to right) of ME jets included. The dashed line corresponds to the maximal number of ME jets reduced by one.
• Figure 4: Differential jet rates for the $1 \to 0$, $2 \to 1$ and $3 \to 2$ transition (top to bottom), for $Q_{\rm cut}=15$ GeV, $30$ GeV, and $100$ GeV (from left to right). The dashed reference curve in each plot is obtained after averaging the corresponding results for $Q_{\rm cut}=15,\,20,\,30,\,50,\,100$ GeV.
• Figure 5: $p_\perp$ of the jet in exclusive $Z+1$jet production. For the jet definition, the Run II $k_\perp$-algorithm with $R=0.4$ and $p_\perp^{\rm jet} > 20$ GeV is used. From left to right, results for $Q_{\rm cut}=15,\,50,\,100$ GeV are contrasted with a reference: the average of the results for $Q_{\rm cut} = 15,\,20,\,30,\,50,\,100$ GeV. The thin horizontal line indicates the jet resolution scale used.