Professor Daniela Bortoletto

Abstract:

A search for physics beyond the standard model in events with at least three leptons and any number of jets is presented. The data sample corresponds to 35 pb-1 of integrated luminosity in pp collisions at s=7 TeV collected by the CMS experiment at the LHC. A number of exclusive multileptonic channels are investigated and standard model backgrounds are suppressed by requiring sufficient missing transverse energy, invariant mass inconsistent with that of the Z boson, or high jet activity. Control samples in data are used to ascertain the robustness of background evaluation techniques and to minimise the reliance on simulation. The observations are consistent with background expectations. These results constrain previously unexplored regions of supersymmetric parameter space. © 2011 CERN.

Abstract:

A measurement of the top-quark mass is presented using Tevatron data from proton-antiproton collisions at center-of-mass energy √s=1.96TeV collected with the CDF II detector. Events are selected from a sample of candidates for production of tt̄ pairs that decay into the lepton+jets channel. The top-quark mass is measured with an unbinned maximum likelihood method where the event probability density functions are calculated using signal and background matrix elements, as well as a set of parametrized jet-to-parton transfer functions. The likelihood function is maximized with respect to the top-quark mass, the signal fraction in the sample, and a correction to the jet energy scale (JES) calibration of the calorimeter jets. The simultaneous measurement of the JES correction (ΔJES) amounts to an additional in situ jet energy calibration based on the known mass of the hadronically decaying W boson. Using the data sample of 578 lepton+jets candidate events, corresponding to 3.2fb-1 of integrated luminosity, the top-quark mass is measured to be mt=172.4±1.4(stat+ΔJES)±1. 3(syst)GeV/c2. © 2011 American Physical Society.