Supersymmetric QCD and CP-violation effects in $t \bar t Z^0$ production at the LHC

Abstract

We investigate the NLO QCD and the CP-violation effects in $t\bar{t}Z^0$ production at the Large Hadron Collider(LHC) in the minimal supersymmetric standard model(MSSM). Our calculation shows that the total NLO QCD correction in the framework of the CP-conserving MSSM significantly improves the scale uncertainty at the leading order, and the contribution from the pure supersymmetric QCD (pSQCD) correction can exceed $-8\%$ with the restrictions of $90~GeV < p_T^t < 120~GeV$ and $120~GeV < p_T^Z < 150~GeV$, where $p_T^t$ and $p_T^Z$ are the transverse momenta of the top-quark and $Z^0$ gauge boson, respectively. Our numerical results demonstrate that the pure SUSY QCD correction generally suppresses the total SM-like QCD correction in the CP-conserving MSSM, and tends to be a constant when either $\tilde{t}_1$ or $\tilde{g}$ is heavy enough. We find also that the CP-odd asymmetry ${\cal A}_{\Phi}$ can reach $2.17 \times 10^{-3}$, if the CP-phase angle really exists in the coupling of gluino-stop-top.