Compatibility and combination of world W-boson mass measurements

TL;DR

This work performs a global, PDF-aware combination of $m_W$ measurements from ATLAS, LHCb, CDF, and D0 (plus LEP) within a coherent model that propagates theory uncertainties and correlations. By emulating each experiment's measurement with a common production/decay description and accounting for detector- and PDF-related shifts, the authors quantify cross-experiment compatibility across multiple PDF sets, with CT18 generally most compatible due to its larger uncertainties. The full combination yields $m_W = 80394.6 \,\pm\, 11.5~\mathrm{MeV}$ under CT18 but with only $0.5\%$ compatibility, while removing the CDF result raises the compatibility to $91\%$ and gives $m_W = 80369.2 \pm 13.3~\mathrm{MeV}$, differing from the CDF value by $3.6\sigma$. The study highlights that PDF model dependence and correlation structure are crucial for precision world averages and that achieving a consistent, high-precision $m_W$ determination will require improved PDF treatments and cross-checks across experiments.

Abstract

The compatibility of W-boson mass measurements performed by the ATLAS, LHCb, CDF, and D0 experiments is studied using a coherent framework with theory uncertainty correlations. The measurements are combined using a number of recent sets of parton distribution functions (PDF), and are further combined with the average value of measurements from the Large Electron-Positron collider. The considered PDF sets generally have a low compatibility with a suite of global rapidity-sensitive Drell-Yan measurements. The most compatible set is CT18 due to its larger uncertainties. A combination of all mW measurements yields a value of mW = 80394.6 +- 11.5 MeV with the CT18 set, but has a probability of compatibility of 0.5% and is therefore disfavoured. Combinations are performed removing each measurement individually, and a 91% probability of compatibility is obtained when the CDF measurement is removed. The corresponding value of the W boson mass is 80369.2 +- 13.3 MeV, which differs by 3.6 sigma from the CDF value determined using the same PDF set.

Figures (10)

• Figure 1: Comparisons between the CDF simulation Aaltonen:2013vwa and the LHC-TeV MWWG simulation for the $m_{\scriptsize\textrm{T}}$ (top) and $p_{\scriptsize\textrm{T}}^{\ell}$ (bottom) distributions.
• Figure 2: Comparisons of the D0 PMCS and the LHC-TeV MWWG simulation for the $m_{\scriptsize\textrm{T}}$ (top) and $p_{\scriptsize\textrm{T}}^{\ell}$ (bottom) distributions.
• Figure 3: Comparison of the published and MWWG simulated $p_{\scriptsize\textrm{T}}^{\ell}$ (top) and $m_{\scriptsize\textrm{T}}$ (bottom) distributions for ATLAS.
• Figure 4: Distributions of generated $p_{\scriptsize\textrm{T}}^{W}$ for $W^\pm$ candidate events in $p\bar{p}$ collisions at CDF and D0 (top), and for $W^+$ and $W^-$ events at ATLAS (bottom). The distributions represent the best-fit model resulting from the analysis of $W$- and $Z$-boson data in the respective experiments, and are shown after all event selection requirements.
• Figure 5: PDF uncertainty correlation matrices for the CT18, MSHT20, NNPDF4.0, and ABMP16 PDF sets, in order from top to bottom.