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

Abstract

We propose that, within the standard model, the correlation between the $t\bar{t}$ forward--backward asymmetry $A_{t\bar{t}}$ 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 mis-measurement of the $t\bar{t}$ system transverse momenta, acceptance cuts, scale dependence and compare the results of MCFM, POWHEG (with & without PYTHIA showering), and SHERPA's CSSHOWER in first-emission mode. We find that the shape of the relative differential distribution $A_l(p_T^l)[A_{t\bar{t}}(p_T^l)]$ 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 $t\bar{t}$ 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.

27 pages, 12 figures

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• Quantum coherence, top transverse polarisation and the Tevatron asymmetry $A_{FB}^{\ell }$
• On the Forward-Backward Asymmetry of Leptonic Decays of $t\bar{t}$ at the Fermilab Tevatron
• Asymmetry Observables for Measuring Spin Correlations in Top-Quark Pair Production
• Top-quark Polarization and Asymmetries at the LHC in the Effective Description of Squark Interactions
• t tbar charge asymmetry, family and friends