First observation of Z+b process at LHC
Events coming from the associated production of the Z boson with at least one bottom-quark jet are studied using proton-proton collisions delivered by the LHC at a centre of mass energy of 7 TeV and recorded by the CMS detector in 2010. The selection of a ﬁnal state with two leptons, electrons or muons, from the Z, and an additional b-tagged jet is described. The event yield and shapes of kinematic variables in 36 pb−1 of data recorded by CMS using single lepton triggers are compared with Monte Carlo predictions from MADGRAPH. In the data sample, 29 (36) events pass the dielectron (dimuon) and high-purity based b-tagging selections, with a measured purity of 0.83 ± 0.10 of Z+b events. For the same b-tagging selection, the ratio σ( Z +b) is found to be 0.054 ± 0.016 (0.046 ± 0.014) in the data for the Z→ ee (Z→ µµ) σ( Z + j) selection, compared to 0.043 ± 0.005 (0.047 ± 0.005) estimated from NLO theory predictions with the same kinematic selections on the leptons and jets than the selections applied to the data.
Reference url: http://cms-physics.web.cern.ch/cms-physics/public/EWK-10-015-pas.pdf