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# Top quark forward-backward asymmetry and same-sign top quark pairs.

High Energy Physics Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
Physical Review Letters (Impact Factor: 7.94). 05/2011; 106(20):201801. DOI:10.1103/PhysRevLett.106.201801
Source: PubMed

ABSTRACT The top quark forward-backward asymmetry measured at the Tevatron collider shows a large deviation from standard model expectations. Among possible interpretations, a nonuniversal Z' model is of particular interest as it naturally predicts a top quark in the forward region of large rapidity. To reproduce the size of the asymmetry, the couplings of the Z' to standard model quarks must be large, inevitably leading to copious production of same-sign top quark pairs at the energies of the Large Hadron Collider (LHC). We explore the discovery potential for tt and ttj production in early LHC experiments at 7-8 TeV and conclude that if no tt signal is observed with 1 fb⁻¹ of integrated luminosity, then a nonuniversal Z' alone cannot explain the Tevatron forward-backward asymmetry.

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##### Article: Probing the Tevatron asymmetry at LHC
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ABSTRACT: Weusean effective operator framework to study the contributions to the Tevatron asymmetry from arbitrary vector bosons and scalars, and compare with their effect on the tail at LHC. Our study shows, for example, that models reproducing the asymmetry by exchange of Z′ and W′ bosons or colour-triplet scalars lead to a large enhancement in the tail at LHC. This fact can be used to exclude these models as the sole explanation for the asymmetry, using the data already collected by CMS and ATLAS. Our analysis is model independent in the sense that we scan over all possible extra particles contributing to the asymmetry, and allow for general couplings. We also explore a class of Standard Model extensions which can accommodate the Tevatron asymmetry without contributing to the total cross section at first order, so that the enhancement of the tail at Tevatron and LHC is moderate.
Journal of High Energy Physics - J HIGH ENERGY PHYS. 01/2011; 2011(5):1-19.
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##### Article: Implications of the CDF t \bar t Forward-Backward Asymmetry for Hard Top Physics
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ABSTRACT: The CDF collaboration has recently reported a large deviation from the standard model of the t \bar t forward-backward asymmetry in the high invariant mass region. We interpret this measurement as coming from new physics at a heavy scale Lambda, and perform a model-independent analysis up to O(1/Lambda^4). A simple formalism to test and constrain models of new physics is provided. We find that a large asymmetry cannot be accommodated by heavy new physics that does not interfere with the standard model. We show that a smoking gun test for the heavy new physics hypothesis is a significant deviation from the standard model prediction for the t \bar t differential cross section at large invariant mass. At M_{t\bar t}>1 TeV the cross section is predicted to be at least twice that of the SM at the Tevatron, and for M_{t\bar t}>1.5 TeV at least three times larger than the SM at the LHC.
Journal of High Energy Physics 03/2011; · 5.62 Impact Factor