We calculate top pair production and decay at the Tevatron pp collider, with the emission of an extra gluon, and study the corresponding W + 5 jet top signals including full spin correlations in the W → ℓν leptonic and W → jj hadronic decays. We study the feasibility of reconstructing W + 5 jet top events with a single b-tag, including realistic energy resolution. Our suggested basic procedure based on kinematic fitting achieves about 74% reconstruction efficiency, with 74% of the reconstructed events correctly classified (purity); this improves to 82% efficiency with 77% purity in double-b-tagged events. We suggest possible refinements, based on virtuality criteria, that give higher purity at the cost of lower reconstruction efficiency.Now that top quark signals have been seen at the Tevatron, in both the dilepton+jets and single-lepton + 4 jets channels and by both the CDF and D0 collaborations [1,2], it is interesting to explore other channels where top signals may be found. The underlying parton mechanism for producing these signals at the Tevatron energy is dominantly q +q → t +t → (bW + )(bW − ),with either one or both of the W bosons decaying leptonically: W → ℓν (ℓ = e, µ).It is important to tag one or more of the b-jets, by a displaced vertex or by a lepton from b-decay, in order to establish the signal and discriminate against background. For determining the top quark mass, it is preferable to study the (W → ℓν) + 4 jets channels, where one of the W -bosons decays hadronically (W → jj) and a suitably chosen three-jet combination has invariant mass m(bjj) ≃ m t , avoiding problems with invisible neutrinos. The principal background in the W + 4 jets channel comes from the electroweak production of a single W -boson plus four QCD jets [3], but with the usual acceptance cuts and b-tagging this background is much smaller than the signal.In high-Q 2 processes like top pair production, it is not uncommon that additional hard QCD radiation (typically a gluon) will be emitted, vizHere the gluon can be radiated either from the incident quarks, or from the produced top quarks before they decay, or from subsequent top decays into bW , and complete calculations have recently been performed [4] exploiting the MADGRAPH program [5].These improve on previous calculations that omitted radiation from top decay [6]; the new results coherently combine the effects of radiation during both production and decay processes, together with their interference. The radiation of gluons from the colordisconnected process of hadronic W -decay (W → jj) can be ignored here, since the hadronically decaying W is identified experimentally as a dijet with invariant mass m(jj) ≃ M W . In the five-jet channel, it seems very likely that the background from W + 5 QCD jets will also be small compared to the signal, after b-tagging.
Basic reconstruction of single-tagged eventsTo make use of the resulting (W → ℓν) + 5 jet final states in the study of top signals, some criteria must be established to distinguish the gluon jet from the other...
