Implications of the CDF t \bar t Forward-Backward Asymmetry for Hard Top Physics

TL;DR

This paper analyzes the large forward-backward asymmetry in top quark pairs reported by CDF, suggesting it indicates new physics at a high energy scale, and proposes a model-independent method to test this hypothesis.

Contribution

It provides a formalism for constraining new physics models based on top quark asymmetry measurements and predicts observable deviations in the top pair production cross section at high invariant masses.

Findings

Large asymmetry cannot be explained by heavy new physics without interference.

Significant deviations in the top pair differential cross section are predicted at high invariant masses.

At M_{tar t}>1 TeV, the cross section is at least twice the SM prediction at the Tevatron.

Abstract

The CDF collaboration has recently reported a large deviation from the standard model of the t \bar t forward-backward asymmetry in the high invariant mass region. We interpret this measurement as coming from new physics at a heavy scale Lambda, and perform a model-independent analysis up to O(1/Lambda^4). A simple formalism to test and constrain models of new physics is provided. We find that a large asymmetry cannot be accommodated by heavy new physics that does not interfere with the standard model. We show that a smoking gun test for the heavy new physics hypothesis is a significant deviation from the standard model prediction for the t \bar t differential cross section at large invariant mass. At M_{t\bar t}>1 TeV the cross section is predicted to be at least twice that of the SM at the Tevatron, and for M_{t\bar t}>1.5 TeV at least three times larger than the SM at the LHC.