Probing for Ultraheavy Quanta at LHC

Experiments at the LHC are sensitive to the presence or absence of matter quanta at mass scales far beyond the scales they can probe directly. The production of $Z$ boson pairs by gluon-gluon fusion is greatly enhanced if there are ultraheavy quanta that carry $SU(3)_{\rm Color}$ and get their mass from electroweak symmetry breaking. For example, a fourth generation quark doublet with an arbitrarily heavy mass would induce a large excess in the $ZZ$ yield that could be detected at the LHC with only $\simeq 10\%$ of the design luminosity.