A sizeable difference in the differential production cross section of top and antitop quarks, respectively, is predicted for hadronically produced heavy quarks. It is of order $\alpha_s$ and arises from the interference between charge odd and even amplitudes respectively. For the TEVATRON it amounts up to 15\% for the differential distribution in suitable chosen kinematical regions. The resulting integrated forward-backward asymmetry of 4--5\% could be measured in the next round of experiments. At the LHC the asymmetry can be studied by selecting appropriately chosen kinematical regions. Furthermore, a slight preference at LHC for centrally produced antitop is predicted, with top quarks more abundant at large positive and negative rapidities.Comment: LaTeX, 16pp, 14 figures, uses revtex. The complete paper, including figures, is also available via anonymous ftp at ftp://ttpux2.physik.uni-karlsruhe.de/ , or via www at http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints

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A sizeable difference in the differential production cross section of top and antitop quarks, respectively, is predicted for hadronically produced heavy quarks. It is of order αs and arises from the interference between charge odd and even amplitudes respectively. For the TEVATRON it amounts up to 15% for the differential distribution in suitable chosen kinematical regions. The resulting integrated forward-backward asymmetry of 4-5% could be measured in the next round of experiments. At the LHC the asymmetry can be studied by selecting appropriately chosen kinematical regions.12.38. Bx, 12.38.Qk, 13.87.Ce, 14.65.Ha Top quark production at hadron colliders has become one of the central issues of theoretical [1] and experimental [2] research. The investigation and understanding of the production mechanism is crucial for the determination of the top quark couplings, its mass and the search for new physics involving the top system. A lot of effort has been invested in the prediction of the total cross section and, more recently, of inclusive transverse momentum distributions [1].In this work we will point to a different aspect of the hadronic production process, which can be studied with a fairly modest sample of quarks. Top quarks produced through light quark-antiquark annihilation will exhibit a sizeable charge asymmetry -an excess of top versus antitop quarks in specific kinematic regions -induced through the interference of the final-state with initial-state radiation (Fig. 1 a, b) and the interference of the box with the lowest-order-diagram ( Fig. 1 c, d). The asymmetry is thus of order α s relative to the dominant production process. In suitable chosen kinematical regions it reaches up to 15%, the integrated forward-backward asymmetry amounts to 4-5%. Top quarks are tagged through their decay t → b W + and can thus be distinguished experimentally from antitop quarks through the sign of the lepton in the semileptonic mode and eventually also through the b-tag. A sample of hundred to two hundred tagged top quarks should in fact be sufficient for a first indication of the effect. Top production at the TEVATRON is dominated by quark-antiquark annihilation, hence the charge asymmetry will be reflected not only in the partonic rest frame but also in the center of mass system of proton and antiproton. The situation is more intricate for proton-proton collisions at the LHC, where no preferred direction is at hand in the laboratory frame. Nevertheless it is also in this case possible to pick kinematical configurations which allow the study of the charge asymmetry.The charge asymmetry has also been investigated in [3] for a top mass of 45 GeV. There, however, only the contribution from real gluon emission was considered requiring the introduction of a physical cutoff on the gluon energy and rapidity to avoid infrared and collinear singularities. Experimentally, however, only inclusive top-antitop 1