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We summarize a search for the top quark with the Collider Detector at Fermilab (CDF) in a sample of Pp collisions at Js =1.8 TeV with an integrated luminosity of 19.3 pb . We find 12 events consistent with either two 8' bosons, or a 8' 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 -)) GeV/c . The tt production cross section is measured to be 13.9 -+)II pb. PACS numbers: 14.65.Ha, 13.85.Ni, 13.85.gk 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%%uo confidence level lower limit of M&,~& 131 GeV/c [1]. Global fits to precision electroweak measurements yield a favored mass of M&,~= 177-+|I+ -I9 GeV/c [2]. One expects that, at Tevatron energies, most top quarks are produced in pairs. For M,o&~85 GeV/c, each top quark decays to a real 8' boson and a b quark.The observed event topology is then determined by the decay mode of the two H bosons. About 5k of the time 226 VOLUME 73, NUMBER 2 PHYSICAL REVIEW LETTERS 11 JULY 1994 both W bosons decay to ev or p v (the "dilepton mode"), giving two high-P~leptons with opposite charge, two b jets, and large missing transverse energy (k"7. ) from the undetected neutrinos [3]. In another 30% of the cases one W boson decays to ev or p v, and the other to a qq' pair (the "lepton+jets mode"). This final state includes a high-Pz charged lepton, k"z, and jets from the 8' and the two b quarks. The remaining 65% of the final states involve the hadronic decays of both W bosons, or the decay of one or both of the 8'bosons into r leptons. These channels have larger backgrounds and are not considered here. This analysis is based on a sample of pp collisions at vs =1. 8 TeV with an integrated luminosity of 19.3

First measurements of the W → ν and Z/γ * → ( = e, µ) production cross sections in proton-proton collisions at √ s = 7 TeV are presented using data recorded by the ATLAS experiment at the LHC. The results are based on 2250 W → ν and 179 Z/γ * → candidate events selected from a data set corresponding to an integrated luminosity of approximately 320 nb −1 . The measured total W and Z/γ * -boson production cross sections times the respective leptonic branching ratios for the combined electron and muon channels are σ tot W · BR(W → ν) = 9.96 ± 0.23(stat) ± 0.50(syst) ± 1.10(lumi) nb and σ tot Z/γ * · BR(Z/γ * → ) = 0.82 ± 0.06 (stat) ± 0.05 (syst) ± 0.09 (lumi) nb (within the invariant mass window 66 < m < 116 GeV). The W/Z cross-section ratio is measured to be 11.7 ± 0.9(stat) ± 0.4(syst). In addition, measurements of the W + and W − production cross sections and of the lepton charge asymmetry are reported. Theoretical predictions based on NNLO QCD calculations are found to agree with the measurements.

Jet cross sections have been measured for the first time in proton-proton collisions at a centre-of-mass energy of 7 TeV using the ATLAS detector. The measurement uses an integrated luminosity of 17 nb −1 recorded at the Large Hadron Collider. The anti-k t algorithm is used to identify jets, with two jet resolution parameters, R = 0.4 and 0.6. The dominant uncertainty comes from the jet energy scale, which is determined to within 7% for central jets above 60 GeV transverse momentum. Inclusive single-jet differential cross sections are presented as functions of jet transverse momentum and rapidity. Dijet cross sections are presented as functions of dijet mass and the angular variable χ. The results are compared to expectations based on next-toleading-order QCD, which agree with the data, providing a validation of the theory in a new kinematic regime.

Web-based search engines such as Google and NorthernLight return documents that are relevant to a user query, not answers to user questions. We have developed an architecture that augments existing search engines so that they support natural language question answering. The process entails five steps: query modulation, document retrieval, passage extraction, phrase extraction, and answer ranking. In this paper we describe some probabilistic approaches to the last three of these stages. We show how our techniques apply to a number of existing search en-