  We propose selection cuts on the LHC top-antitop production sample which
should enhance the sensitivity to New Physics signals in the study of the
top-antitop invariant mass distribution. We show that selecting events in which
the top-antitop object has little transverse and large longitudinal momentum
enlarges the quark-fusion fraction of the sample and therefore increases its
sensitivity to New Physics which couples to quarks and not to gluons. We find
that systematic error bars play a fundamental role and assume a simple model
for them. We check how a non-visible new particle would become visible after
the selection cuts enhance its resonance bump. A final realistic analysis
should be done by the experimental groups with a correct evaluation of the
systematic error bars.
