Measurement of the Z/gamma* + bb-jets cross section in pp collisions at sqrt(s) = 7 TeV with the CMS detector

The production of up to two b quarks, in association with a Z boson decaying into two leptons, is studied using proton-proton collisions delivered by the LHC at a centre-of-mass energy of 7 TeV and recorded by the CMS detector. The inclusive cross section of the Z+bb process with Z$/\gamma^*\rightarrow\ \ell\ell$ (where $\ell\ell$ = ee or $\mu\mu$) is measured with a data sample collected in 2011, corresponding to an integrated luminosity of 2.1\,fb$^{-1}$. The cross section and the kinematic properties of the events predicted by the \textsc{MadGraph} event generator interfaced with \textsc{pythia} for the parton shower are compared with the data for b jets with $p_{\mathrm{T}} > 25$ GeV and $|\eta| < 2.1$. The Z+bb cross section times branching fraction of the Z to leptons for events with the dilepton invariant mass in $76 < M_{\ell\ell} < 106$ GeV, $p_{\mathrm{T}}^{\ell} > 20$ GeV, $|\eta^{\ell}| < 2.5$ and at least two b hadron jets with $p_{\mathrm{T}} > 25$ GeV and $|\eta| < 2.1$ and a separation between the leptons and any jet of $\Delta R > 0.5$, is found to be $0.37 \pm 0.02(\mathrm{stat.}) \pm 0.07(\mathrm{syst.}) \pm 0.02(\mathrm{theory})$\,pb. The Z+b production in association with any number of b jets is found to be $3.78 \pm 0.05(\mathrm{stat.}) \pm 0.31(\mathrm{syst.}) \pm 0.11(\mathrm{theory}) \mathrm{pb}$.