  At the LHC, top quark pairs are dominantly produced from gluons, making it
difficult to measure the top quark forward-backward asymmetry. To improve the
asymmetry measurement, we study variables that can distinguish between top
quarks produced from quarks and those from gluons: the invariant mass of the
top pair, the rapidity of the top-antitop system in the lab frame, the rapidity
of the top quark in the top-antitop rest frame, the top quark polarization and
the top-antitop spin correlation. We combine all the variables in a likelihood
discriminant method to separate quark-initiated events from gluon-initiated
events. We apply our method on models including G-prime's and W-prime's
motivated by the recent observation of a large top quark forward-backward
asymmetry at the Tevatron. We have found that the significance of the asymmetry
measurement can be improved by 10% to 30%. At the same time, the central values
of the asymmetry increase by 40% to 100%. We have also analytically derived the
best spin quantization axes for studying top quark polarization as well as
spin-correlation for the new physics models.
