Searches for Resonances Decaying to Top

The top quark was discovered in 1995 by the CDF and D0 collaborations [2, 3]. During Run I (1992-1996) both experiments collected a data set of about 125 pb. In 2001 Run II has started operating with a center-of-mass-energy of √ s = 1.96 TeV and an increased luminosity. One of the main aims is to further investigate the properties of top quarks. End of 2006 there was first evidence for single top production [4]. At present, the top quark mass is measured with a precision of 0.8% [5] and the tt̄ production cross section is measured with a precision of about 11% [6]. CDF and D0 have recorded more than 3 fb of data. The increased size of top quark samples allows to precisely study the production mechanism of top quarks and to search for physics beyond the standard model (SM). In the SM there is no resonant production of tt̄ pairs. The only exception might be a heavy higgs boson decaying to tt̄. However, many models beyond the SM suggest yet unknown resonances. There are Z-like bosons in extended gauge theories [7], Kaluza Klein excitations of the gluon or Z boson [8, 9], axigluons [10], resonances in topcolor models [11], and others. Top quarks almost exclusively decay into to W boson and a b quark. The final state of a tt̄ event is determined by the decay modes of the to W bosons. The presented searches are performed in the lepton + jets channel tt̄ → WWbb̄ → lν̄lqq̄′bb̄. In the final state there is one isolated high pT lepton (l = e, μ), ≥ 4 jets, and missing ET . Both experiments apply b−tagging to improve the signal-to-background ratio. The main background is the SM tt̄ production. In the following a search for a narrow width resonance by the D0 experiment [12], and a search for a massive gluon [13] and a measurement of the differential cross section dσ/dMtt̄ [14] by the CDF experiment is presented.