Professor Daniela Bortoletto

Abstract:

A measurement of the inclusive cross section for the process pp → bb̄X → μμX′ at √ s = 7TeV is presented, based on a data sample corresponding to an integrated luminosity of 27.9 pb-1 collected by the CMS experiment at the LHC. By selecting pairs of muons each with pseudorapidity |η| < 2:1, the value σ(pp → bb̄X → μμX′) = 26:4 ± 0:1 (stat.) ±2:4 (syst.) ±1:1 (lumi.) nb is obtained for muons with transverse momentum pT > 4 GeV, and 5:12±0:03 (stat.) ±0:48 (syst.) ±0:20 (lumi.) nb for pT > 6 GeV. These results are compared to QCD predictions at leading and next-to-leading orders.

Abstract:

The inclusive production cross sections for forward jets, as well for jets in dijet events with at least one jet emitted at central and the other at forward pseudorapidities, are measured in the range of transverse momenta pT = 35-150 GeV/c in proton-proton collisions at √ s = 7TeV by the CMS experiment at the LHC. Forward jets are measured within pseudorapidities 3.2 < |η| < 4.7, and central jets within the |η| < 2:8 range. The differential cross sections d2sigma;/dpT dη are compared to predictions from three approaches in perturbative quantum chromodynamics: (i) next-to-leading-order calculations obtained with and without matching to parton-shower Monte Carlo simulations, (ii) pythia and herwig parton-shower event generators with different tunes of parameters, and (iii) cascade and hej models, including different non-collinear corrections to standard single-parton radiation. The single-jet inclusive forward jet spectrum is well described by all models, but not all predictions are consistent with the spectra observed for the forward-central dijet events. Copyright CERN.

Abstract:

A measurement of the mass difference between the top and the antitop quark (Δmt = mt - mt) is performed using events with a muon or an electron and at least four jets in the final state. The analysis is based on data collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 4:96±0:11 fb-1, and yields the value of δmt = -0:44±0:46 (stat.)±0:27 (syst.) GeV. This result is consistent with equality of particle and antiparticle masses required by CPT invariance, and provides a significantly improved precision relative to existing measurements. © Copyright CERN.

Abstract:

A measurement is presented of the relative prompt production rate of χc2 and χc1 with 4.6 fb-1 of data collected by the CMS experiment at the LHC in pp collisions at √s = 7 TeV. The two states are measured via their radiative decays χc→J/ψ+γ, with the photon converting into an e+e- pair for J/ψ rapidity {pipe}y(J/ψ){pipe}<1.0 and photon transverse momentum pT(γ)>0.5 GeV/c. The measurement is given for six intervals of pT(J/ψ) between 7 and 25 GeV/c. The results are compared to theoretical predictions. © 2012 CERN for the benefit of the CMS collaboration.

Abstract:

The first measurement of the charged component of the underlying event using the novel "jet-area/median" approach is presented for proton-proton collisions at centre-of-mass energies of 0.9 and 7 TeV. The data were recorded in 2010 with the CMS experiment at the LHC. A new observable, sensitive to soft particle production, is introduced and investigated inclusively and as a function of the event scale defined by the transverse momentum of the leading jet. Various phenomenological models are compared to data, with and without corrections for detector effects. None of the examined models describe the data satisfactorily. © 2012 SISSA.