Professor Daniela Bortoletto

Abstract:

A search for pair-production of first generation scalar leptoquarks is performed in the final state containing an electron, a neutrino, and at least two jets using proton-proton collision data at √s=7 TeV. The data were collected by the CMS detector at the LHC, corresponding to an integrated luminosity of 36 pb-1. The number of observed events is in good agreement with the predictions for standard model processes. Prior CMS results in the dielectron channel are combined with this electron+neutrino search. A 95% confidence level combined lower limit is set on the mass of a first generation scalar leptoquark at 339 GeV for β=0.5, where β is the branching fraction of the leptoquark to an electron and a quark. These results represent the most stringent direct limits to date for values of β greater than 0.05. © 2011 CERN.

Abstract:

This Letter reports a measurement of the cross section of prompt isolated photon pair production in pp̄ collisions at a total energy √s=1.96TeV using data of 5.36fb-1 integrated luminosity collected with the CDF II detector at the Fermilab Tevatron. The measured cross section, differential in basic kinematic variables, is compared with three perturbative QCD predictions, a leading order parton shower calculation and two next-to-leading order calculations. The next-to-leading order calculations reproduce most aspects of the data. By including photon radiation from quarks before and after hard scattering, the parton shower prediction becomes competitive with the next-to-leading order predictions.

Abstract:

Using data corresponding to 6.0fb-1 of pp̄ collisions at √s=1.96TeV collected by the CDF II detector, we present a cross section measurement of top-quark pair production with an additional radiated photon in the central region with 10 GeV or more of transverse energy tt̄γ. The events are selected by looking for a lepton (ℓ or μ), a photon (γ), significant transverse momentum imbalance (ET), large total transverse energy, and three or more jets, with at least one identified as containing a b quark (b). Using an event selection optimized for the tt̄γ candidate sample, we also measure the cross section of tt̄ (σtt̄). We measure the tt̄γ cross section (σtt̄γ) to be 0.18±0.08pb, and the ratio of σtt̄γ to σtt̄ to be 0.024±0.009. We observe a probability of 0.0015 (3.0 standard deviations) of the background (non-tt̄γ events alone producing 30 events or more. © 2011 American Physical Society.

Abstract:

The observation of the bottom, strange baryon Ξb0 through the decay chain Ξb0→Ξc+π-, where Ξc+→Ξ -π+π+, Ξ -→Λπ-, and Λ→pπ-, is reported by using data corresponding to an integrated luminosity of 4.2fb-1 from pp̄ collisions at √s=1.96TeV recorded with the Collider Detector at Fermilab. A signal of 25.3-5.4+5.6 candidates is observed whose probability of arising from a background fluctuation is 3.6×10-12, corresponding to 6.8 Gaussian standard deviations. The Ξb0 mass is measured to be 5787.8±5.0(stat)±1.3(syst)MeV/ c2. In addition, the Ξb- baryon is observed through the process Ξb-→Ξc0π-, where Ξc0→Ξ -π+, Ξ-→Λπ-, and Λ→pπ-. © 2011 American Physical Society.