Mass dependent top forward backward asymmetry in the effective Lagrangian approach: Addendum to "Model independent analysis of the forward-backward asymmetry of top quark production at the Tevatron"

TL;DR

This paper investigates the top quark forward-backward asymmetry using an effective Lagrangian with dimension-6 contact interactions, finding that within its validity, the model underestimates the observed asymmetry, suggesting possible new physics at a few hundred GeV.

Contribution

It provides a model-independent analysis of the top FB asymmetry with dimension-6 operators and compares predictions with experimental data, highlighting limitations of the effective approach.

Findings

Mass dependent top FB asymmetry is smaller than experimental data within the effective theory.

Discrepancy exceeds 2-sigma, indicating potential need for new physics.

Effective Lagrangian approach may be inadequate if future data confirms current deviations.

Abstract

Recently the CDF and the D0 Collaborations presented the data on the top forward-backward (FB) asymmetry A_FB as functions of M_(t t^bar) and \Delta y = y_t - y_t^bar. We study these observables in the effective Lagrangian approach with dimension-6 q q^bar t t^bar contact interactions, and compare with the CDF and D0 data. When we stay within the validity region of the effective Lagrangian approach, the mass dependent top FB asymmetry turns out to be smaller than the CDF data, more than 2-sigma away. If this discrepancy remains in the future data with better statistics, it would imply that the effective Lagrangian approach is not adequate for the top FB asymmetry, and a new physics scale around a few hundred GeV in the t- or u-channel may be responsible for the observed top FB asymmetry.