Professor Daniela Bortoletto

Abstract:

The inclusive b-jet production cross section in pp collisions at a center-ofmass energy of 7TeV is measured using data collected by the CMS experiment at the LHC. The cross section is presented as a function of the jet transverse momentum in the range 18 < pT < 200 GeV for several rapidity intervals. The results are also given as the ratio of the b-jet production cross section to the inclusive jet production cross section. The measurement is performed with two different analyses, which differ in their trigger selection and b-jet identification: a jet analysis that selects events with a b jet using a sample corresponding to an integrated luminosity of 34 pb-1, and a muon analysis requiring a b jet with a muon based on an integrated luminosity of 3 pb-1. In both approaches the b jets are identified by requiring a secondary vertex. The results from the two methods are in agreement with each other and with next-to-leading order calculations, as well as with predictions based on the pythia event generator.

Abstract:

A measurement of the J/ ψ and ψ (2S) production cross sections in pp collisions at √s = 7TeV with the CMS experiment at the LHC is presented. The data sample corresponds to an integrated luminosity of 37 pb -1. Using a fit to the invariant mass and decay length distributions, production cross sections have been measured separately for prompt and non-prompt charmonium states, as a function of the meson transverse momentum in several rapidity ranges and integrated in the kinematical regions considered in this study. In addition, cross sections restricted to the acceptance of the CMS detector are given, which are not affected by the polarization of the charmonium states. The ratio of the differential production cross sections of the two states, where systematic uncertainties largely cancel, is also determined. The branching fraction of the inclusive B → ψ (2S)X decay is extracted from the ratio of the non-prompt cross sections to be: B(B → ψ (2S)X) = (3:08 ± 0:12 (stat.+syst.) ± 0:13 (theor.) ± 0:42 (BPDG)) × 10-3: B(B → ψ(2S)X) = (3.08 ± 0.12 (stat.+syst.) ± 0.13 (theor.) ± 0.42 (BPDG)) × 10-3.

Abstract:

Measurements of jet production rates in association with W and Z bosons for jet transverse momenta above 30 GeV are reported, using a sample of proton-proton collision events recorded by CMS at √s = 7TeV, corresponding to an integrated luminosity of 36 pb-1. The study includes the measurement of the normalized inclusive rates of jets σ(V+ ≥ n jets)=σ(V), where V represents either a W or a Z. In addition, the ratio of W to Z cross sections and the W charge asymmetry as a function of the number of associated jets are measured. A test of scaling at √s = 7TeV is also presented. The measurements provide a stringent test of perturbative-QCD calculations and are sensitive to the possible presence of new physics. The results are in agreement with the predictions of a simulation that uses explicit matrix element calculations for final states with jets. © 2012 SISSA.

Abstract:

The production of b jets in association with a Z/γ*boson is studied using proton-proton collisions delivered by the LHC at a centre-of-mass energy of 7TeV and recorded by the CMS detector. The inclusive cross section for Z/γ*+b-jet production is measured in a sample corresponding to an integrated luminosity of 2.2 fb-1. The Z/γ*+b-jet cross section with Z/γ*→ℓℓ (where ℓ ℓ = ee or μ μ) for events with the invariant mass 60 < Mℓ ℓ < 120 GeV, at least one b jet at the hadron level with pT > 25 GeV and |η|< 2:1, and a separation between the leptons and the jets of ΔR > 0:5 is found to be 5:84±0:08 (stat:) ±0:72 (syst:) -0:55+0:25 (theory) pb. The kinematic properties of the events are also studied and found to be in agreement with the predictions made by the MadGraph event generator with the parton shower and the hadronisation performed by pythia.