arXiv:1008.0742v2 [hep-ph] 10 Nov 2010 MZ-TH/10-28 Top-Quark Forward-Backward Asymmetry in Randall-Sundrum Models Beyond the Leading Order M. Bauer, F. Goertz, U. Haisch, T. Pfoh and S. Westhoff Institut f¨ur Physik (THEP), Johannes Gutenberg-Universit¨at D-55099 Mainz, Germany Abstract We calculate thet¯tforward-backward asymmetry,At FB, in Randall-Sundrum (RS) models taking into account the dominant next-to-leading order (NLO) corrections in QCD. At Born level we include the exchange of Kaluza-Klein (KK) gluons and photons, theZ boson and its KK excitations, as well as the Higgs boson, whereas beyond the leading order (LO) we consider the interference of tree-level KK-gluon exchange with one-loop QCD box diagrams and the corresponding bremsstrahlungs corrections.We find that the strong suppression of LO effects, that arises due to the elementary nature and the mostly vector-like couplings of light quarks, is lifted at NLO after paying the price of an additional factor ofαs/(4π). In spite of this enhancement, the resulting RS corrections inAt FBremain marginal, leaving the predicted asymmetry SM-like.As our arguments are solely based on the smallness of the axial-vector couplings of light quarks to the strong sector, our findings are model-independent and apply to many scenarios of new physics that address the flavor problem via geometrical sequestering.
Contents 1Introduction1 2Top-Antitop Production in the SM4 3Cross Section and Asymmetry in RS Models6 3.1Calculation of LO Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 3.2Calculation of NLO Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 4Numerical Analysis14 5Conclusions and Outlook19 AHiggs-Boson Phase-Space Factors21 BWilson Coefficients in the ZMA21 CRG Evolution of the Wilson Coefficients23 DParameter Points23 1Introduction The top quark is the heaviest particle in the Standard Model (SM) of particle physics.Its large mass suggests that it might be deeply connected to the mechanism driving electroweak symmetry breaking. Detailed experimental studies of the top-quark properties are thus likely to play a key role in unravelling the origin of mass, making top-quark observables one of the cornerstones of the Fermilab Tevatron and CERN Large Hadron Collider (LHC) physics programmes. Up to now, the CDF and DØ experiments at the Tevatron have collected thousands of top-quark pair events, which allowed them to measure the top-quark mass,mt, and its total inclusive cross section,σt¯t, with an accuracy of below 1% [1] and 10% [2, 3], respectively. While these measurements are important in their own right, from the point of view of searches for physics beyond the SM, determinations of kinematic distributions and charge asymmetries int¯tproduction are more interesting, since these observables are particularly sensitive to non-standard dynamics. Such searches have been performed at the Tevatron [4, 5, 6], and a result for thet¯tinvariant mass spectrum,dσt¯t/dMt¯t, has been recently obtained from data collected at CDF [7, 8].The forward-backward asymmetry,At FB, has also been measured [9, 10, 11, 12, 13] and constantly found to be larger than expected.In the laboratory (p¯p) frame the most recent CDF result reads (At FB )p¯p exp= (15.0±5.0stat.±2.4syst.) %,(1) 1
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