Abstract
A search is presented for a massive particle, generically referred to as a Z0, decaying into a tt pair. The search focuses on Z0 resonances that are sufficiently massive to produce highly Lorentz-boosted top quarks, which yield collimated decay products that are partially or fully merged into single jets.
The analysis uses new methods to analyze jet substructure, providing suppression of the non-top multijet backgrounds. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 5 fb1.
Upper limits in the range of 1 pb are set on the product of the production cross section and branching fraction for a topcolor Z0 modeled for several widths, as well as for a Randall- Sundrum Kaluza-Klein gluon. In addition, the results constrain any enhancement in tt production beyond expectations of the standard model for tt invariant mass larger than 1 TeV/c2.