StandardModelFurtherResultsWZJets

Introduction

This page collects ATLAS public results from the Standard Model W/Z+jets physics subgroup that were approved after the submission of the CSC chapter "Production of jets in association with Z bosons".

Additional Results from the CSC Group (approved July 2008)

Event selection

Z→e⁺e^-

Z→μ⁺μ^-

W→eν

W→μν

Lepton triggering and reconstruction

Figure 1: Electron trigger efficiency (left) and electron reconstruction efficiency (right) as a function of number of jets in the event. The trigger efficiency drops with hadronic activity, but the reconstruction efficiency is stable. The efficiency is measured with a tag-and-probe method, and the MC histograms are derived from MC truth information.

Signal efficiency and background rates

Figure 2: Jet multiplicity distributions for Z→ee (top left), Z→μμ (top right), W→eν (bottom left), and W→μν (bottom right).

Figure 3: Transverse momentum distributions for the leading jet in Z→ee (top left), Z→μμ (top right), W→eν (bottom left), and W→μν (bottom right).

Figure 4: Transverse momentum distributions for the second-leading jet in Z→ee (left) and Z→μμ (right).

Figure 5: Dilepton invariant mass distributions for Z→ee (left) and Z→μμ (right).

Figure 6: Transverse mass of electron and missing energy in W→eν events.

Figure 7: Transverse momentum of jets in Z→μ&mu + jet events before (left) and after (right) applying b-tagging. The b-tagging algorithm is the SV1 and IP3D combination.

Systematic uncertainties

Figure 8: Jet multiplicity with uncertainties due to jet energy scale. Plots show the jet multiplicity distributions for Z→μμ (top left), W→eν (middle left), and W→μν (bottom left), plus the relative uncertainty for Z→μμ (top right), W→eν (middle right), and W→μν (bottom right).

Figure 9: Leading jet transverse momentum distribution with uncertainties due to jet energy scale. Plots show the leading jet pT distributions for Z→μμ (top left), W→eν (top right), plus the relative uncertainties for Z→μμ (bottom left), W→eν (bottom right).

Figure 10: Impact of PDF uncertainty on W→eν analysis. We have reweighted the sample from CTEQ6LL (used at generation) to the central value of CTEQ6M. The CTEQ6M error sets are used to calculate the uncertainties on the leading jet pT (left) and the relative uncertainty on the distribution (right).

Figure 11: Impact of PDF uncertainty on W→eν analysis. We have reweighted the sample from CTEQ6LL (used at generation) to the central value of CTEQ6M. The CTEQ6M error sets are used to calculate the uncertainties on the jet η distribution (left) and the relative uncertainty on the distribution (right).

Comparisons with theory

Figure 12: The detector effects in observed distributions must be unfolded for comparison with theory. These plots show the corrections in the Z→ee channel for electron reconstruction and trigger efficiency, as well as the corrections for the jet reconstruction efficiency and resolution. The hadron-level distributions from Monte Carlo truth are recovered for the leading jet pT distribution (left) and the second-leading jet pT distribution (right).

Figure 13: An additional unfolding or correction takes the results from the hadron level back to the parton level for comparisons. These corrections to the jet pT distributions account for fragmentation (left) or for fragmentation and underlying event (right). The corrections decrease with increasing jet pT.

Figure 14: Fully-simulated ALPGEN Monte Carlo distributions from Z→ee events are corrected, using all previous correction factors, for comparison with the MCFM cross section calculation. The jet multiplicity (left) and leading jet momentum (right) are plotted with statistical errors expected from a 1 fb^-1 sample. A JES uncertainty of 3% is used in this unfolding exercise.

Figure 15: Relative uncertainties on the data-theory comparison in Z→ee events, including the uncertainties from all sources. The uncertainties are given for the jet multiplicity spectrum (left) and the leading jet pT distribution (right). Note the JES uncertainty scales of 5% and 10%.

Responsible: JasonNielsen
Last reviewed by: Never reviewed