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

Abstract

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±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(FB)(D∅)=0.106±0.03 and about 1.5σ below that of CDF [T. Aaltonen et al. (CDF Collaboration), Phys. Rev. D 87, 092002 (2013)] A(FB)(CDF)=0.164±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.

Simultaneous measurement of forward-backward asymmetry and top polarization in dilepton final states fromtt¯production at the Tevatron

“…5. The NLO SM prediction for A tt is A tt = (9.5 ± 0.7)% [2], while the SM polarization is expected to be small, κP = (−0.19±0.05)% [4]. Our measurement is consistent with the SM prediction within the 68% confidence level region.…”

“…The value of A tt at parton level without applying any selection requirement is A tt = (5.23 ± 0.07 (stat))%, which is smaller than a SM prediction [2] that includes higher order effects.…”

“…The interferences with electroweak processes increase the asymmetry. In the SM, the asymmetry is predicted to be ≈ 10% [1][2][3]. Within the SM, the longitudinal polarizations of the top quark and antiquark are due to parity violating electroweak contributions to the production process.…”

NNLO QCD predictions for fully-differential top-quark pair production at the Tevatron

“…The current paper extends our previous work [10] on top-quark A FB by presenting a detailed study of next-to-next-to leading order (NNLO) QCD corrections to differential A FB and related differential distributions in the following variables: tt rapidity difference ∆y ≡ y t − yt, ∆y and m tt as well as ∆y and tt transverse momentum p T,tt . We also present NNLO QCD corrections to the slopes of A FB in the variables ∆y and m tt , as well as to the lowest few Legendre moments that have been measured by CDF [2,3] in the context of A FB .…”

“…We study the p T,tt cumulative asymmetry which, as already indicated in ref. [10], allows one to better understand the origin of higher-order QCD corrections to A FB . Finally, we present the NNLO QCD prediction for the cumulative m tt asymmetry and discuss it in the context of recent predictions [11] based on the Principle of Maximum Conformality (PMC) [12].…”