Search for light top squarks in p(p)over-bar collisions at root s=1.8 TeV

We present a search for pair produced top squarks, the supersymmetric partners of the top quark, using the D0 detector at the Fermilab Tevatron pp̄ collider. We consider a scenario in which the lighter of the two top squarks t̃ l decays with 100% branching fraction to a charm quark and the lightest neutralino X̃ 1 0 yielding a signal of two acollinear jets with missing transverse energy. We observe 3 events while we expect 3.5 ± 1.2 events from the known standard model processes. We exclude at the 95% confidence level a significant region of the mt̃1-mX̃10 parameter space. The highest mt̃1 value we exclude is 93 GeV/c 2 with a corresponding mmX̃10 value of 8 GeV/c 2

Studies of topological distributions of inclusive three- and four-jet events in p(p)over-bar collisions at root s=1800GeV with the D0 detector

The global topologies of inclusive three- and four-jet events produced in p̄p interactions are described. The three- and four-jet events are selected from data recorded by the DO detector at the Fermilab Tevatron Collider operating at a center-of-mass energy of √s = 1800 GeV. The measured, normalized distributions of various topological variables are compared with parton-level predictions of tree-level QCD calculations. The parton-level QCD calculations are found to be in good agreement with the data. The studies also show that the topological distributions of the different subprocesses involving different numbers of quarks are very similar and reproduce the measured distributions well. The parton-shower Monte Carlo generators provide a less satisfactory description of the topologies of the three- and four-jet events. © 1996 The American Physical Society

J/ψ production in pp̄ collisions at √s = 1.8 TeV

We have studied J/ψ production in pp̄ collisions at √s = 1.8 TeV with the DØ detector at Fermilab using μ+/μ- data. We have measured the inclusive J/ψ production cross section as a function of J/ψ transverse momentum, pT. For the kinematic range pT > 8 GeV/c and |η\ < 0.6 we obtain σ(pp̄ → J/ψ + X) ·Br(J/ψ → μ+μ-) = 2.08 ± 0.17(stat) ± 0.46(syst) nb. Using the muon impact parameter we have estimated the fraction of J/ψ mesons coming from B meson decays to be fb = 0.35 ± 0.09(stat)±0.10(syst) and inferred the inclusive b production cross section. From the information on the event topology the fraction of nonisolated J/ψ events has been measured to be fnonisol = 0.64 ± 0.08(stat)±0.06(syst). We have also obtained the fraction of J/ψ events resulting from radiative decays of χc states, fχ = 0.32 ± 0.07(stat)±0.07(syst). We discuss the implications of our measurements for charmonium production processes