The ratio of the cross section for p (p) over bar interactions producing a Z boson and at least one b-quark jet to the inclusive Z + jet cross section is measured using 4.2 fb(-1) of p (p) over bar collisions collected with the D0 detector at the Fermilab Tevatron collider at sqrt(s) = 1.96 TeV. The Z -} l(+) l- candidate events with at least one b jet are discriminated from Z + charm and light jet(s) events by a novel technique that exploits the properties of the tracks associated to the jet.
The measured ratio is 0: 0193 +/- 0: 0027 for events having a jet with transverse momentum p(T) } 20 GeV and pseudorapidity vertical bar eta vertical bar {= 2.5, which is the most precise to date and is consistent with theoretical predictions.