Professor Daniela Bortoletto

Abstract:

This Letter reports a measurement of the top quark mass, Mtop, in data from pp¯ collisions at s=1.96 TeV corresponding to 2.7 fb−1 of integrated luminosity at the Fermilab Tevatron using the CDF II detector. Events with the lepton+jets topology are selected. An unbinned likelihood is constructed based on the dependence of the lepton transverse momentum, PT, on Mtop. A maximum likelihood fit to the data yields a measured mass Mtop=176.9±8.0stat±2.7syst GeV/c2. In this measurement, the contribution by the jet energy scale uncertainty to the systematic error is negligible. The result provides an important consistency test for other Mtop measurements where explicit use of the jet energy is made for deriving the top quark mass.

Abstract:

We report the first observation of two Cabibbo-suppressed decay modes of the Bs0 meson. Using a sample of pp̄ collisions at √s=1.96TeV corresponding to 5.9fb-1 of integrated luminosity collected with the CDF II, the collider detector at the Fermilab Tevatron, we search for new Bs0 decay modes in a sample of events containing J/ψ→μ+μ - decays. We reconstruct a Bs0→J/ψK*(892)0 signal with K*(892)0→K+π-, observing a yield of 151±25 events with a statistical significance of 8.0σ. We also reconstruct a Bs0→J/ψKS0 signal with KS0→π+π-, observing a yield of 64±14 events with a statistical significance of 7.2σ. From these yields, we extract the branching ratios B(Bs0→J/ψK*(892)0)=(8. 3±3.8)×10-5 and B(Bs0→J/ψK0)=(3.5±0.8) ×10-5, where statistical, systematic, and fragmentation- fraction uncertainties are included in the combined uncertainty. © 2011 American Physical Society.

Abstract:

A search for a heavy gauge boson W' has been conducted by the CMS experiment at the LHC in the decay channel with an electron and large transverse energy imbalance ETmiss, using proton-proton collision data corresponding to an integrated luminosity of 36 pb-1. No excess above standard model expectations is seen in the transverse mass distribution of the electron- ETmiss system. Assuming standard-model-like couplings and decay branching fractions, a W' boson with a mass less than 1.36 TeV/c2 is excluded at 95% confidence level. © 2011 CERN.

Abstract:

We report on a measurement of b-hadron lifetimes in the fully reconstructed decay modes B(+)→J/ψK(+), B⁰→J/ψK*(892)⁰, B⁰→J/ψK(s)⁰, and Λ(b)⁰→J/ψΛ⁰ using data corresponding to an integrated luminosity of 4.3 fb⁻¹, collected by the CDF II detector at the Fermilab Tevatron. The measured lifetimes are τ(B(+))=[1.639±0.009(stat)±0.009(syst)] ps, τ(B⁰)=[1.507±0.010(stat)±0.008(syst)] ps, and τ(Λ(b)⁰)=[1.537±0.045(stat)±0.014(syst)] ps. The lifetime ratios are τ(B(+))/τ(B⁰)=[1.088±0.009(stat)±0.004(syst)] and τ(Λ(b)⁰)/τ(B⁰)=[1.020±0.030(stat)±0.008(syst)]. These are the most precise determinations of these quantities from a single experiment.

Abstract:

We present a search for a new narrow, spin-1, high mass resonance decaying to μ(+)μ⁻+X, using a matrix-element-based likelihood and a simultaneous measurement of the resonance mass and production rate. In data with 4.6 fb⁻¹ of integrated luminosity collected by the CDF detector in pp collisions at √s=1960 GeV, the most likely signal cross section is consistent with zero at 16% confidence level. We therefore do not observe evidence for a high mass resonance and place limits on models predicting spin-1 resonances, including M>1071 GeV/c² at 95% confidence level for a Z' boson with the same couplings to fermions as the Z boson.