Confronting Top AFB with Parity Violation Constraints

TL;DR

This paper examines how low-energy parity violation experiments constrain t-channel mediator models proposed to explain the top forward-backward asymmetry, ruling out many such models due to their predicted effects on nuclear weak charge.

Contribution

It provides a detailed analysis of how atomic parity violation constraints impact t-channel models for top AFB, highlighting the importance of low-energy tests in new physics searches.

Findings

Parity violation constraints disfavor models with >20% AFB at M_tt > 450 GeV

One-loop contributions from flavor-violating mediators affect nuclear weak charge

Future proton weak charge measurements will further constrain these models

Abstract

We consider the implications of low-energy precision tests of parity violation on t-channel mediator models explaining the top AFB excess measured by CDF and D0. Flavor-violating u-t or d-t couplings of new scalar or vector mediators generate at one-loop an anomalous contribution to the nuclear weak charge. As a result, atomic parity violation constraints disfavor at >3 sigma t-channel models that give rise to a greater than 20% AFB at the parton level for M_tt > 450 GeV while not producing too large a top cross-section. Even stronger constraints are expected through future measurements of the proton weak charge by the Q-Weak experiment.