Abstract
The production of a Z boson, decaying into two leptons and produced in association with one or more b jets, is studied using proton-proton collisions delivered by the LHC at a centre-of-mass energy of 7 TeV. The data were recorded in 2011 with the CMS detector and correspond to an integrated luminosity of 5 inverse femtobarns. The Z(ll) + b-jets cross sections (where ll = mu mu or ee) are measured separately for a Z boson produced with exactly one b jet and with at least two b jets. In addition, a cross section ratio is extracted for a Z boson produced with at least one b jet, relative to a Z boson produced with at least one jet. The measured cross sections are compared to various theoretical predictions, and the data favour the predictions in the five-flavour scheme, where b quarks are assumed massless. The kinematic properties of the reconstructed particles are compared with the predictions from the MADGRAPH event generator using the PYTHIA parton shower simulation.
Highlights
The characteristics of the production of a Z boson in association with b hadrons have been studied at the LHC by the Compact Muon Solenoid (CMS) Collaboration [12]
The reconstruction and selection of events with a Z boson that decays into a pair of muons or electrons, and one or more b jets are based on the criteria used in the measurement of the inclusive Z+b-jets cross section at CMS [9]
These results indicate that the difference observed with mcfm is specific to the modelling of the Z+b-jets final state
Summary
The data used in this analysis were collected with the Compact Muon Solenoid (CMS) detector. The cross section for the Z+jets sample, 3048 pb, is normalized to match the next-to-NLO prediction for inclusive Z production obtained with fewz [28] and the CTEQ6m PDFs [27]. The simulated Z+jets sample is split into three subsamples, according to the underlying production of b jets, c jets, or jets originating only from gluons or u,d,s quarks (hereafter called light-parton jets), with no requirement on the pT or η of the jets. These subsamples are labelled Z+b, Z+c, and Z+l, respectively
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