Professor Daniela Bortoletto

Abstract:

A search is presented for physics beyond the standard model (BSM) in events with a Z boson, jets, and missing transverse energy (ETmiss). This signature is motivated by BSM physics scenarios, including supersymmetry. The study is performed using a sample of proton-proton collision data collected at √s=7 TeV with the CMS experiment at the LHC, corresponding to an integrated luminosity of 4.98 fb -1. The contributions from the dominant standard model backgrounds are estimated from data using two complementary strategies, the jet-Z balance technique and a method based on modeling ETmiss with data control samples. In the absence of evidence for BSM physics, we set limits on the non-standard-model contributions to event yields in the signal regions and interpret the results in the context of simplified model spectra. Additional information is provided to facilitate tests of other BSM physics models. © 2012 CERN.

Abstract:

Results are presented from searches for the standard model Higgs boson in proton-proton collisions at s=7 and 8 TeV in the Compact Muon Solenoid experiment at the LHC, using data samples corresponding to integrated luminosities of up to 5.1 fb-1 at 7 TeV and 5.3 fb-1 at 8 TeV. The search is performed in five decay modes: γγ, ZZ, W+W-, τ+τ-, and bb-. An excess of events is observed above the expected background, with a local significance of 5.0 standard deviations, at a mass near 125 GeV, signalling the production of a new particle. The expected significance for a standard model Higgs boson of that mass is 5.8 standard deviations. The excess is most significant in the two decay modes with the best mass resolution, γγ and ZZ; a fit to these signals gives a mass of 125.3±0.4(stat.)±0.5(syst.) GeV. The decay to two photons indicates that the new particle is a boson with spin different from one. © 2012 CERN.

Abstract:

The results of a search for pair production of a heavy, top-like quark, t ', in the decay mode t't-'→bW+b-W-→bℓ+νb-ℓ-ν- are presented. The search is performed with a data sample corresponding to an integrated luminosity of 5.0fb -1 in pp collisions at a center-of-mass energy of 7 TeV, collected by the CMS experiment at the LHC. The observed number of events agrees with the expectation from standard model processes, and no evidence of t't-' production is found. Upper limits on the production cross section as a function of t ' mass are presented, and t ' masses below 557GeV/c 2 are excluded at the 95% confidence level. © 2012 CERN.

Abstract:

A search for high-mass resonances decaying into τ +τ - is performed using a data sample of pp collisions at s=7TeV. The data were collected with the CMS detector at the LHC and correspond to an integrated luminosity of 4.9 fb -1. The number of observed events is in agreement with the standard model prediction. An upper limit on the product of the resonance cross section and branching fraction into τ-lepton pairs is calculated as a function of the resonance mass. Using the sequential standard model resonance ZSSM' and the superstring-inspired E 6 model with resonance Zψ' as benchmarks, resonances with standard model couplings with masses below 1.4 and 1.1 TeV, respectively, are excluded at 95% confidence level. © 2012 CERN.