EVIDENCE FOR TOP QUARK PRODUCTION IN PP COLLISIONS AT S = 1.8 TEV

We summarize a search[1] for the top quark with the Collider Detector at Fermilab (CDF) in a sample of pp collisions at √ s= 1.8 TeV with an integrated luminosity of 19.3 pb−1. We find 12 events consistent with either two W bosons, or a W boson and at least one b jet. The probability that the measured yield is consistent with the background is 0.26%. Though the statistics are too limited to establish firmly the existence of the top quark, a natural interpretation of the excess is that it is due to tt production. Under this assumption, constrained fits to individual events yield a top quark mass of 174± 10 −12 GeV/c 2. The tt production cross section is measured to be 13.9 −4.8 pb. PACS numbers: 14.80.Dq, 13.85.Qk, 13.85.Ni, 02.20.Fh The Standard Model has enjoyed outstanding success, yet the top quark, which is required as the weak-isospin partner of the bottom quark, has remained unobserved. Direct searches at the Fermilab Tevatron have placed a 95% confidence level lower limit of Mtop > 131 GeV/c [2]. Global fits to precision electroweak measurements yield a favored mass of Mtop = 174 +11+17 −12−19 GeV/c 2 [3].