Observation of Top Quark Production in [ ̄ over p]p Collisions with the Collider Detector at Fermilab

Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. We establish the existence of the top quark using a 67 pb ' data sample of pp collisions at ~s = 1.8 TeV collected with the Collider Detector at Fermilab (CDF). Employing techniques similar to those we previously published, we observe a signal consistent with tt decay to WWbb, but inconsistent with the background prediction by 4.8o.. Additional evidence for the top quark is provided by a peak in the reconstructed mass distribution. We measure the top quark mass to be 176 ~ 8(stat) ~ 10(syst) GeV/c2, and the tt production cross section to be 6.8+24 pb. Recently the Collider Detector at Fermilab (CDF) Collaboration presented the first direct evidence for the top quark [I], the weak isodoublet partner of the b quark required in the standard model. We searched for tt pair production with the subsequent decay tt ~ WbWb. The observed topology in such events is determined by the decay mode of the two W bosons. Dilep-ton events (eIL, ee, and ~p,) are produced primarily when both W bosons decay into ev or p, v. Events in the lepton + jets channel (e, p, + jets) occur when one W boson decays into leptons and the other decays into quarks. To suppress background in the lepton + jets mode, we identify b quarks by reconstructing secondary vertices from b decay (SVX tag) and by finding additional leptons from b semileptonic decay (SLT tag). In Ref. [I] we found a 2. 8o. excess of signal over the expectation from background.