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Carbon nitride nanosheets (NS-C N ) were found to undergo robust binding with a binuclear ruthenium(II) complex (RuRu') even in basic aqueous solution. A hybrid material consisting of NS-C N (further modified with nanoparticulate Ag) and RuRu' promoted the photocatalytic reduction of CO to formate in aqueous media, in conjunction with high selectivity (approximately 98 %) and a good turnover number (>2000 with respect to the loaded Ru complex). These represent the highest values yet reported for a powder-based photocatalytic system during CO reduction under visible light in an aqueous environment. We also assessed the desorption of RuRu' from the Ag/C N surface, a factor that can contribute to a loss of activity. It was determined that desorption is not induced by salt additives, pH changes, or photoirradiation, which partly explains the high photocatalytic performance of this material.

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

The kinematic properties of t t events are studied in the Wϩmultijet channel using data collected with the CDF detector during the 1992-1995 runs at the Fermilab Tevatron collider corresponding to an integrated luminosity of 109 pb Ϫ1 . Distributions of a variety of kinematic variables chosen to be sensitive to different aspects of t t production are compared with those expected from Monte Carlo calculations. A sample of 34 events rich in t t pairs is obtained by requiring at least one jet identified by the silicon vertex detector ͑SVX͒ as having a displaced vertex consistent with the decay of a b hadron. The data are found to be in good agreement with predictions of the leading order t t matrix element with color coherent parton shower evolution. ͓S0556-2821͑99͒04007-2͔