Professor Daniela Bortoletto

Abstract:

A search for the rare decays B0s → μ+μ- and B0 → μ+ μ- is performed in pp collisions at ps = 7TeV, with a data sample corresponding to an integrated luminosity of 5 fb-1 collected by the CMS experiment at the LHC. In both decays, the number of events observed after all selection requirements is consistent with the expectation from background plus standard model signal predictions. The resulting upper limits on the branching fractions are B(B0s → μ+ μ-) < 7:7 × 10-9 and B(B0 → μ+μ-) < 1:8 × 10-9 at 95% confidence level.

Abstract:

A search for the standard model Higgs boson decaying into two Z bosons with subsequent decay into a final state containing two quark jets and two leptons, H → ZZ*(→) ! qq-ℓ ℓ+ is presented. Results are based on data corresponding to an integrated luminosity of 4.6 fb-1 of proton-proton collisions at ps = 7TeV, collected with the CMS detector at the LHC. In order to discriminate between signal and background events, kinematic and topological quantities, including the angular spin correlations of the decay products, are employed. Events are further classiéd according to the probability of the jets to originate from quarks of light or heavy avor or from gluons. No evidence for the Higgs boson is found, and upper limits on its production cross section are determined for a Higgs boson of mass between 130 and 600 GeV.

Abstract:

Results are presented on a search for a light charged Higgs boson that can be produced in the decay of the top quark t → H+b and which, in turn, decays into τ+νt. The analysed data correspond to an integrated luminosity of about 2 fb-1 recorded in protonproton collisions at √s = 7 TeV by the CMS experiment at the LHC. The search is sensitive to the decays of the top quark pairs tt̄ → H±W∓bb̄ and tt̄ → H ±H∓bb̄. Various final states have been studied separately, all requiring presence of a τ lepton from H+ decays, missing transverse energy, and multiple jets. Upper limits on the branching fraction B(t → H+b) in the range of 2-4% are established for charged Higgs boson masses between 80 and 160 GeV, under the assumption that B(H+ → τ+ντ) = 1.

Abstract:

A search for anomalous production of events with three or more isolated leptons in pp collisions at √ s = 7TeV is presented. The data, corresponding to an integrated luminosity of 4:98 fb-1, were collected by the CMS experiment at the LHC during the 2011 run. The search is applicable to any model of new physics that enhances multiple lepton production. The observed multilepton events are categorized into exclusive search channels based on the identity and kinematics of the objects in the events. An estimate of the standard-model background rates from data is emphasized, but simulation is also used to estimate some of the background rates. The search results are interpreted in the context of supersymmetry, including both R-parity-conserving and R-parity-violating models. We derive exclusion limits as a function of squark, gluino, and chargino masses.

Abstract:

A search is presented for a massive particle, generically referred to as a Z', decaying into a tt̄ pair. The search focuses on Z' resonances that are sufficiently massive to produce highly Lorentz-boosted top quarks, which yield collimated decay products that are partially or fully merged into single jets. The analysis uses new methods to analyze jet substructure, providing suppression of the non-top multijet backgrounds. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 5 fb-1. Upper limits in the range of 1 pb are set on the product of the production cross section and branching fraction for a topcolor Z' modeled for several widths, as well as for a Randall-Sundrum Kaluza-Klein gluon. In addition, the result contrain any enhancement in tt̄ production beyond expectations of the standard mode for tt invariant mass larger than 1TeV/c2.