Top Quark Production Cross Section at the Tevatron

Since the discovery of the top quark by the CDF and DØ Collaborations 1, Tevatron remains the world’s only experimental facility where it’s properties can be investigated. In pp̄ collisions top quarks are dominantly produced in pairs via strong interaction. Depending on the decay modes of the W -bosons, one expects three distinctive event topologies from the tt̄ → WbWb̄ signal: a di-lepton final state with 2 high-pT isolated leptons, 2 jets, and missing ET (6 ET ) from escaping neutrinos; a lepton+jets final state with a high-pT lepton, 4 jets and 6 ET ; and an all-jets final state consisting of 6 jets. While the di-lepton channel gives the cleanest signal, it amounts to only 5% of the tt̄ sample (considering only e and μ), whereas the all-jets state constitutes 44% of the total fraction, but suffers from a huge QCD multijet background. The lepton+jets final state, forming 30% of tt̄ events, is the best compromise between purity and the statistics. At the Tevatron the top quark can also be produced singly, via electroweak interaction This mechanism has not been observed yet, and remains subject of active searches at the Tevatron2.