Resolving the Tevatron Top Quark Forward-Backward Asymmetry Puzzle: Fully Differential Next-to-Next-to-Leading-Order Calculation

We determine the dominant missing standard model (SM) contribution to the top quark pair forward-backward asymmetry at the Tevatron. Contrary to past expectations, we find a large, around 27%, shift relative to the well-known value of the inclusive asymmetry in next-to-leading order QCD. Combining all known standard model corrections, we find that $A_{FB}^{SM}=0.095\pm 0.007$. This value is in agreement with the latest DØ measurement [V. M. Abazov et al. (D0 Collaboration), Phys. Rev. D 90, 072011 (2014)] $A_{\mathrm{FB}}^{\mathrm{D}\varnothing }=0.106\pm 0.03$ and about $1.5\sigma$ below that of CDF [T. Aaltonen et al. (CDF Collaboration), Phys. Rev. D 87, 092002 (2013)] $A_{\mathrm{FB}}^{\mathrm{CDF}}=0.164\pm 0.047$. Our result is derived from a fully differential calculation of the next-to-next-to leading order (NNLO) QCD corrections to inclusive top pair production at hadron colliders and includes—without any approximation—all partonic channels contributing to this process. This is the first complete fully differential calculation in NNLO QCD of a two–to–two scattering process with all colored partons.

Figure 1

The inclusive asymmetry in pure QCD (black) and $\mathrm{QCD}+\mathrm{EW}$ [28] (red). Capital letters (NLO, NNLO) correspond to the unexpanded definition Eq (2), while small letters (nlo, nnlo) to the definition Eq. (3). The CDF/DØ (naive) average is from Ref. [29]. Error bands are from scale variation only. Our final prediction corresponds to scenario 10.

Figure 2

The $|\mathrm{\Delta }y|$ differential asymmetry in pure QCD at NLO (blue) and NNLO (orange) versus CDF [6] and DØ [15, 44] data. Error bands are from scale variation only. For improved readability some bins are plotted slightly narrower. The highest bin contains overflow events.

Figure 3

As in Fig. 2 but for the $M_{t\overline{t}}$ differential asymmetry. The highest bin contains overflow events and the lowest bin includes all events down to the production threshold $2m_t$.

Figure 4

As in Fig. 2 but for the $P_{T,t\overline{t}}$ differential asymmetry.