Measurement of the Inclusive Forward-Backward tt Production Asymmetry and its Rapidity Dependence dAfb/d(y).

Abstract

Early measurements of a large forward-background asymmetry at the CDF and D0 experiments at Fermilab have generated much recent interest, but were hampered by large uncertainties. We present here a new measurement of the corrected forward-backward asymmetry of pair-produced top quarks, using a high-statistics sample with much improved precision. We study the rapidity, ytop, of the top quark production angle with respect to the incoming parton momentum in both the lab and tt rest frames. We find the corrected forward-backward asymmetries to be Afb(pp) = 0.150 ± 0.050stat ± 0.024syst Afb(tt) = 0.158 ± 0.072stat ± 0.024syst These results should be compared with the small lab pp frame charge asymmetry expected in QCD at NLO, Afb = 0.050 ± 0.015 [7, 8, 9, 10]. Additionally, we introduce a measurement of the Afb rapidity dependence dAfb/d(delta y). We find this to be Afb(|delta y| < 1.0) = 0.026 ± 0.104stat ± 0.012syst Afb(|delta y| > 1.0) = 0.611 ± 0.210stat ± 0.246syst which we compare with model predictions 0.039 ± 0.006 and 0.123 ± 0.018 for the inner and outer rapidities, respectively.