Speaker
Description
Electroweak production of a Z boson in association with two jets (EW Zjj) provides a clean way of probing vector boson fusion (VBF) and is a crucial test of the electroweak couplings within the Standard Model at high energies. Using the ATLAS detector at the Large Hadron Collider, this analysis measures differential cross sections in the dilepton channel, focusing on the characteristic VBF topology with two forward jets of high transverse momentum, large invariant mass ($m_{jj}$), and large rapidity separation ($\Delta y_{jj}$). The measurement uses the full Run 2 dataset at $\sqrt{s} = 13$ TeV (139 fb$^{-1}$) and most of the available Run 3 dataset at $\sqrt{s} = 13.6$ TeV (164 fb$^{-1}$), enabling independent measurements with increased sensitivity in the high-$m_{jj}$ and high-$\Delta y_{jj}$ regions where the EW contributions dominate. A central challenge of the EW Zjj measurement at a hadron collider is the suppression of the dominant QCD-induced Z+jets background, which closely mimics the signal topology but lacks the characteristic colour-singlet exchange. Previous measurements in this channel have identified reliance on QCD simulation as a primary bottleneck in extracting precise EW yields from data. This work presents a background-estimation strategy using an extended maximum likelihood fit that is designed to have reduced sensitivity to the choice of prior QCD modelling. The fit extracts the primary background normalization and data-driven fractional background scaling factors from two control regions with additional jet activity. The background yields in the signal region and in a third control region, defined by the absence of additional jet activity, are simultaneously corrected using the extracted scaling factors. Our preliminary studies indicate that this approach enables electroweak measurements with reduced systematic uncertainties. The proposed strategy has been rigorously stress-tested and shown to be minimally biased and stable under variations in the prior modelling of both signal and background from simulation. The resulting measurements using ATLAS data are expected to provide a valuable benchmark for interpretations within the Effective Field Theory (EFT) framework.
| Keyword-1 | ATLAS |
|---|---|
| Keyword-2 | Electroweak Physics |
| Keyword-3 | High Energy Physics |