Speculations on the W-Mass Measurement at CDF

TL;DR

This paper analyzes the W-mass measurement discrepancy at CDF, exploring possible new physics explanations through electroweak fits and models, and discusses collider implications and constraints from LHC data.

Contribution

It provides a comprehensive analysis of the W-mass anomaly using electroweak fits and evaluates various new physics models for their compatibility with experimental data.

Findings

Electroweak fits reveal tensions between different $m_W$ measurements.

Certain models like fermiophobic $Z'$ and vector-like top partners can explain the discrepancy.

LHC constraints significantly restrict the parameter space of proposed explanations.

Abstract

The W Mass determination at the Tevatron CDF experiment reported a deviation from the SM expectation at 7$\sigma$ level. We discuss a few possible interpretations and their collider implications. We perform electroweak global fits under various frameworks and assumptions. We consider three types of electroweak global fits in the effective-field-theory framework: the $S$-$T$, the $S$-$T$-$\delta G_F$, and the eight-parameter flavor-universal one. We discuss the amounts of tensions between different $m_W$ measurements reflected in these fits and the corresponding shifts in central values of these parameters. With these electroweak fit pictures in hand, we present a few different classes of models and discuss their compatibility with these results. We find that while explaining the $m_W$ discrepancy, the single gauge boson extensions face strong LHC direct search constraints unless the $Z'$ is fermiophobic (leptophobic) which can be realized if extra vector fermions (leptons) mix with the SM fermions (leptons). Vector-like top partners can partially generate the needed shift to the electroweak observables. The compatibility with top squark is also studied in detail. We find non-degenerate top squark soft masses enhance the needed operator coefficients, enabling an allowed explanation compatible with current LHC measurements. Overall, more theory and experimental developments are highly in demand to reveal the physics behind this discrepancy.