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Abstract:

We have measured the cross sections d²Ïƒ/d P Tdη) for production of isolated direct photons in ppÌ„ collisions at two different center-of-mass energies, 1.8 TeV and 0.63 TeV, using the Collider Detector at Fermilab. The normalization of both data sets agrees with the predictions of quantum chromodynamics for a photon transverse momentum (PT) of 25 GeV/c, but the shapes versus photon PT do not. These shape differences lead to a significant disagreement in the ratio of cross sections in the scaling variable x^T(≡ 2PT/√s). This disagreement in the xT ratio is difficult to explain with conventional theoretical uncertainties such as scale dependence and parton distribution parametrizations. © 2002 The American Physical Society.

Abstract:

We report on measurements of the branching ratios of the decays B⁺→Xcl⁰(1P)K⁺ and B⁺ →J/ψ°­⁺Ï€⁺Ï€^-, where Xcl⁰(1P)→J/ψγ and J/ψ→μ⁺μ^- in pp collisions at √s= 1.8 TeV. Using a data sample from an integrated luminosity of 110 pb^-1 collected by the Collider Detector at Fermilab we measure the branching ratios to be BR(B⁺→Xcl⁰(1P) K⁺)=15.5±5.4(stat)±1.5(syst)±1.3(br)× 10^-4 and BR(B⁺ →J/ψ°­⁺Ï€⁺Ï€^-)=6.9 ±1.8(stat)±1.1(syst)±0.4(br)×10^-4 where (br) is due to the finite precision on BR(B^-→J/ψ°­⁺), BR(Xcl⁰(1P)→J/ψγ)is used to normalize the signal yield, and (syst) encompasses all other systematic uncertainties.

Abstract:

We have searched for evidence of physics beyond the standard model in events that include an energetic photon and an energetic b-quark jet, produced in 85 pb^-1 of pÌ„p collisions at 1.8 TeV at the Tevatron Collider at Fermilab. This signature, containing at least one gauge boson and a third-generation quark, could arise in the production and decay of a pair of new particles, such as those predicted by supersymmetry, leading to a production rate exceeding standard model predictions. We also search these events for anomalous production of missing transverse energy, additional jets and leptons (e, μ, and Ï„), and additional b quarks. We find no evidence for any anomalous production of γb or γb + X events. We present limits on two supersymmetric models: a model where the photon is produced in the decay χ̃2⁰→ γχ̃1⁰, and a model where the photon is produced in the neutralino decay into the gravitino LSP, χ̃1⁰→ γG̃. We also present our limits in a model-independent form and test methods of applying model-independent limits.

Abstract:

We present a detailed examination of the heavy flavor content of the W+jet data sample collected with the Collider Detector at Fermilab during the 1992-1995 collider run at the Fermilab Tevatron. Jets containing heavy flavor quarks are selected via the identification of secondary vertices or semileptonic decays of b and c quarks. There is generally good agreement between the rates of secondary vertices and soft leptons in the data and in the standard model simulation including single and pair production of top quarks. An exception is the number of events in which a single jet has both a soft lepton and a secondary vertex tag. In W+2,3 jet data, we find 13 such events where we expected 4.4±0.6 events. The kinematic properties of this small sample of events are statistically difficult to reconcile with the simulation of standard model processes.