$A_{FB}^t$ Meets LHC

Abstract

The recent Tevatron measurement of the forward-backward asymmetry of the top quark shows an intriguing discrepancy with Standard Model expectations, particularly at large $\text{ttbar}$ invariant masses. Measurements of this quantity are subtle at the LHC, due to its $pp$ initial state, however, one can define a forward-central-charge asymmetry which captures the physics. We study the capability of the LHC to measure this asymmetry and find that within the SM a measurement at the $5\sigma$ level is possible with roughly 60 fb${}^{-1}$ at $\sqrt{s}=14$ TeV. If nature realizes a model which enhances the asymmetry (as is necessary to explain the Tevatron measurements), a significant difference from zero can be observed much earlier, perhaps even during early LHC running at $\sqrt{s}=7$ TeV. We further explore the capabilities of the 7 TeV LHC to discover resonances or contact interactions which modify the $\text{ttbar}$ invariant mass distribution using recent boosted top tagging techniques. We find that TeV-scale color octet resonances can be discovered, even with small coupling strengths and that contact interactions can be probed at scales exceeding 6 TeV. Overall, the LHC has good potential to clarify the situation with regards to the Tevatron forward-backward measurement.

Comments: 21 page, 8 figures; references added and minor improvements to analysis; conclusions unchanged