Professor Daniela Bortoletto

Abstract:

We present a new method to measure the top quark pair production cross section and the background rates with data corresponding to an integrated luminosity of 2.7fb-1 from pp̄ collisions at √s=1.96TeV collected with the CDF II Detector. We select events with a single electron or muon candidate, missing transverse energy, and at least one b-tagged jet. We perform a simultaneous fit to a jet flavor discriminant across nine samples defined by the number of jets and b tags. An advantage of this approach is that many systematic uncertainties are measured in situ and inversely scale with integrated luminosity. We measure a top cross section of σ tt̄=7.64±0.57(stat+syst)±0.45(luminosity)pb. © 2011 American Physical Society.

Abstract:

A comparison of the relative yields of Υ resonances in the μ+μ- decay channel in Pb-Pb and pp collisions at a center-of-mass energy per nucleon pair of 2.76TeV is performed with data collected with the CMS detector at the LHC. Using muons of transverse momentum above 4GeV/c and pseudorapidity below 2.4, the double ratio of the Υ(2S) and Υ(3S) excited states to the Υ(1S) ground state in Pb-Pb and pp collisions, [Υ(2S+3S)/Υ(1S)]Pb-Pb/[Υ(2S+3S)/Υ(1S) ]pp, is found to be 0.31-0.15+0.19(stat)±0.03(syst). The probability to obtain the measured value, or lower, if the true double ratio is unity, is calculated to be less than 1%. © 2011 American Physical Society.

Abstract:

Using Zγ candidate events collected by the CDF detector at the Tevatron Collider, we search for potential anomalous (non-standard-model) couplings between the Z boson and the photon. Zγ couplings vanish at tree level and are heavily suppressed at higher orders; hence any evidence of couplings indicates new physics. Measurements are performed using data corresponding to an integrated luminosity of 4.9fb-1 in the Z→νν̄ decay channel and 5.1fb-1 in the Z→l +l- (l=μ, e) decay channels. The combination of these measurements provides the most stringent limits to date on Zγ trilinear gauge couplings. Using an energy scale of Λ=1.5TeV to allow for a direct comparison with previous measurements, we find limits on the CP-conserving parameters that describe Zγ couplings to be |h3γ,Z|<0.022 and |h4γ,Z|<0.0009. These results are consistent with standard model predictions. © 2011 American Physical Society.

Abstract:

A search for new dielectron-mass resonances using data recorded by the CDF II detector and corresponding to an integrated luminosity of 5.7fb-1 is presented. No significant excess over the expected standard model prediction is observed. In this data set, an event with the highest dielectron mass ever observed (960GeV/c2) was recorded. The results are interpreted in the Randall-Sundrum (RS) model. Combined with the 5.4fb-1 diphoton analysis, the RS-graviton lower-mass limit for the coupling k/M ̄Pl=0.1 is 1058GeV/c2, making it the strongest limit to date. © 2011 American Physical Society.