Evidence for a Mass Dependent Forward-Backward Asymmetry in Top Quark Pair Production

Authors
Dan Amidei, Myron Campbell, Andrew Eppig, Dave Mietlicki
Glenn L Strycker, Monica Tecchio, Alexei Varganov, Tom Wright
University of Michigan

Robin Erbacher, Thomas A Schwarz
University of California, Davis

Joey Huston
Michigan State University

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Arxiv: hep-ex/1101.0034

We present a new measurement of the inclusive forward-backward tt production asymmetry and its rapidity and mass dependence. The measurements are performed with data corresponding to an integrated luminosity of 5.3 fb⁻¹ of pp collisions at √s = 1.96 TeV, recorded with the CDF II Detector at the Fermilab Tevatron. Significant inclusive asymmetries are observed in both the laboratory frame and the ttbar rest frame, and in both cases are found to be consistent with CP conservation under interchange of t and t. In the ttbar rest frame, the asymmetry is observed to increase with the t-t rapidity difference, Δy, and with the invariant mass of the tt system. Fully corrected parton-level asymmetries are derived in two regions of each variable, and the asymmetry is found to be most significant at large Δy and M_tt. For M_tt > 450 GeV/c2, the parton-level asymmetry in the tt rest frame is A = 0.475 ± 0.114 compared to a next-to-leading order QCD prediction of 0.088 ± 0.013.