Closing the window on the axigluon mass using top quark production data

The contribution of axigluons (the massive color-octet gauge bosons in all chiral color models) to top quark pair production in hadronic collisions is considered. The agreement between the experimental values of the tt̄ production cross-section at the TEVATRON and recent QCD predictions is used to discuss limits on the axigluon mass. Specifically, intermediate mass axigluons, those in the mass range 50 GeV < M_A < 120 GeV which has not already been excluded, would increase the tree-level qq̄ → tt̄ cross-section by a factor of ≥ 2, thereby increasing the theoretical predictions for σ_tt̄ by Δσ_tt̄ = 3.2-3.7 pb (2.5-2.9 pb) using two different leading-order parton distributions over this mass range, independent of the axigluon decay width. Such an increase is roughly 1.3-1.6 (0.8-1.1) standard deviations larger than that suggested by the apparent good agreement between combined experimental results and recent theoretical calculations and so is not ruled out, but is definitely disfavored. Future high-statistics top-quark production runs will likely make a more definitive statement. The forward-backward asymmetry in tt̄ production induced by axigluons in this mass window is also discussed and found to be quite large and so could provide another constraint.