Data driving the top quark forward-backward asymmetry with a lepton-based handle

We propose that, within the standard model, the correlation between the tt̄ forward-backward asymmetry A_tt̄ and the corresponding lepton-based asymmetry A_l - at the differential level - is strong and rather clean both theoretically and experimentally. Hence a combined measurement of the two distributions as a function of the lepton p_T, a direct and experimentally clean observable, would lead to a potentially unbiased and normalization-free test of the standard model prediction. To check the robustness of our proposal, we study how the correlation is affected by mismeasurement of the tt̄ system transverse momenta, acceptance cuts, and scale dependence and compare the results of mcfm, powheg (with and without pythia showering), and sherpa's csshower in first-emission mode. We find that the shape of the relative differential distribution A_l(pTl)[A _tt̄(pTl)] is only moderately distorted, hence supporting the usefulness of our proposal. Beyond the first emission, we find that the correlation is not accurately captured by lowest-order treatment. We also briefly consider other differential variables such as the system transverse mass and the canonical tt̄ invariant mass. Finally, we study new physics scenarios where the correlation is significantly distorted and therefore can be more readily constrained or discovered using our method.