Professor Daniela Bortoletto

Abstract:

We present a measurement of the differential cross section dσ/dΣE^jetT for the production of multijet events in pp collisions where the sum is over all jets with transverse energy E^jetT > E^minT. The measured cross section for events with E^jetT > 320 GeV is compared to O(α³s) perturbative QCD predictions and QCD parton shower Monte Carlo predictions. The agreement between the O(α³s) predicted and observed event rates is reasonable for E^minT = 100 GeV, but poorer for E^minT = 20 GeV. © 1998 The American Physical Society.

Abstract:

We present the first general measurements (invariant-mass, transverse-energy, and angular distributions) of the process, (Formula presented) (Formula presented) using data collected by the CDF at Fermilab. We compare the data with predictions from a tree-level QCD calculation and the PYTHIA shower Monte Carlo program. Our data sample is particularly sensitive to contributions from initial- and final-state radiation of photons and jets. Using the PYTHIA Monte Carlo program, we contrast the kinematical distributions for direct photon production with those for initial- and final-state photon radiation (bremsstrahlung). Based on the angular distributions, we find that our data favor a mixture of bremsstrahlung and direct photon production, as predicted, over either process alone. © 1998 The American Physical Society.

Abstract:

We search for the flavor-changing neutral current decays of the top quark t → λ and t → qZ (here represents the c and u quarks) in pp collisions at √s = 1.8 TeV. We use a dataset (∫ L dt˜ 110pb-1) collected during the 1992-1995 run of the Collider Detector at Fermilab. We set 95% confidence level limits on the branching fractions B(t → qλ) < 3.2% and B(t → qZ) < 33%, consistent with the standard model. © 1998 The American Physical Society.

Abstract:

We search for new long-lived particles which decay to Z0 bosons by looking for Z0→e+e- decays with displaced vertices. We find no evidence for parent particles pf the Z0 with long lifetimes in 90 pb-1 of data from the CDF experiment at Fermilab. We set a cross section limit as a function of the lifetime of the parent particle for both a generic Z0 parent and a fourth-generation, charge -1/3 quark that decays into Z0b. © 1998 The American Physical Society.