Measurement of ttbar forward-backward asymmetry at CDF

by Dante Amidei (University of Michigan)

Tuesday 29 Mar 2011, 11:00 → 12:00 Europe/Zurich

Early measurements of the forward-backward ttbar production asymmetry at CDF and D0 suggested significant asymmetries that have been interpreted as evidence for exotic gluon partners or new t-channel interactions. We present new measurements performed with 5 fb-1 of Tevatron ppbar collisions at Ecm = 1.96 TeV, recorded and analyzed at CDF. Significant inclusive asymmetries are observed in both the lepton+jets and the dilepton decay modes of the ttbar pair. In the dilepton mode, the asymmetry is observed in the reconstructed top rapidity, and in the lepton rapidity difference, which is independent of any top reconstruction. In the lepton plus jets sample, the full reconstruction of the top kinematics is used to measure the dependence of the asymmetry on the tt bar rapidity difference Delta(y) and the invariant mass M_(ttbar ) of the ttbar system. The asymmetry is found to be most significant at large Delta(y) and M_(ttbar) . For M_(ttbar) > 450 GeV/c2, the parton-level asymmetry in the t-tbar rest frame is A = 0.475 ± 0.114 compared to a next-to-leading order QCD prediction of 0.088 ± 0.013. The asymmetry is found to be consistent with CP conservation under interchange of t and tbar.

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