Modeling uncertainties on the Z boson background in the context of high precision W boson mass measurements

Abstract The precise determination of the W boson mass, $$m_W$$ m W , is a cornerstone of electroweak precision tests and a critical input to global fits of the Standard Model (SM). While most existing measurements of $$m_W$$ m W are in agreement with SM predictions, the recent result from the CDF collaboration exhibits a significant deviation from the SM prediction but also exceeding $$4\sigma $$ 4 σ from the global average of all other high precision measurements. This prompts renewed scrutiny of potential sources of systematic bias. In this study, we investigate the modeling of the Z boson background, which is particularly relevant in the muon decay channel of the W boson, where undetected muons can mimic missing transverse momentum. Using updated theoretical predictions and high-precision simulations, we construct reweighted templates to evaluate the impact of possible mismodeling in the Z background. Our analysis suggests that such effects can induce a shift in the extracted $$m_W$$ m W value of up to 8 MeV in the muon decay channel. While this shift is non-negligible and exceeds the originally quoted uncertainty from this source, it remains insufficient to explain the full discrepancy observed in the CDF measurement.