[Paper Review] Impact of the recent measurements of the top-quark and W-boson masses on electroweak precision fits

J. de Blas, M. Pierini+2 more|arXiv (Cornell University)|Apr 8, 2022

Particle physics theoretical and experimental studies31 citations

TL;DR

The paper assesses how the CMS top-quark mass and the CDF W-boson mass measurements affect electroweak precision fits in the SM and beyond, comparing SM predictions with new averages and exploring oblique and SMEFT scenarios.

ABSTRACT

We assess the impact of the very recent measurement of the top-quark mass by the CMS Collaboration on the fit of electroweak data in the Standard Model and beyond, with particular emphasis on the prediction for the mass of the W boson. We then compare this prediction with the average of the corresponding experimental measurements including the new measurement by the CDF Collaboration, and discuss its compatibility in the Standard Model, in new physics models with oblique corrections, and in the dimension-six Standard Model Effective Field Theory. Finally, we present the updated global fit to electroweak precision data in these models.

Motivation & Objective

• Evaluate the impact of the new top-quark mass measurement on electroweak precision data fits within the Standard Model and beyond.
• Compare the SM prediction for the W-boson mass with new experimental averages including the CDF result.
• Explore the compatibility of the updated fits with oblique new physics models and the SMEFT framework.
• Provide updated global fits to electroweak precision observables under standard and conservative averaging scenarios.

Proposed method

• Perform Bayesian global fits of electroweak precision observables (EWPO) using the HEPfit code with state-of-the-art SM calculations.
• Construct new averages for m_t and M_W from latest CMS, Tevatron, ATLAS, CMS Run 2, and LHCb measurements, including a conservative averaging scenario.
• Calculate SM predictions for M_W from EWPO fits omitting M_W input and compare to experimental averages.
• Study NP implications in oblique (S, T, U) parameter space and in the dimension-six SMEFT Warsaw basis.
• Report posterior distributions and information criteria (IC) for SM, oblique, and SMEFT fits.

Experimental results

Research questions

• RQ1 How do the latest top-quark mass measurements affect the electroweak precision fit and the predicted W-boson mass in the SM?
• RQ2 Does the updated M_W average reconcile with the SM prediction, or hint at New Physics?
• RQ3 Can oblique corrections (S, T, U) alleviate any tensions between the SM prediction and the M_W measurement?
• RQ4 What are the implications of a dimension-six SMEFT description for EWPO in light of the new measurements?

Key findings

• The SM prediction for M_W under the standard average is significantly discrepant with the new measurement, exhibiting a 6.5 sigma tension when excluding the measurement from the fit and a 3.7 sigma tension under a conservative averaging strategy.
• Oblique NP fits with U set to zero can reduce the tension to about 1.5 sigma, while allowing nonzero U yields compatibility with the data.
• SMEFT fits indicate correlations among leptonic operators and show that certain combinations of Wilson coefficients can accommodate the M_W measurement, with specific coefficients (e.g., hat{C}_{\