Jeff Tseng

Abstract:

A search for new physics in the exclusive γ∄T channel was performed. Departure from the expected standard model cross section was found. Limits on two specific models of new physics were defined. Furthermore, the limit in a "pseudomodel-independent" manner was detailed.

Abstract:

We have measured the cross sections d²σ/d P Tdη) for production of isolated direct photons in pp̄ 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/ψK⁺π⁺π^-, 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/ψK⁺π⁺π^-)=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/ψK⁺), 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 p̄p 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 τ), 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.