Measurement of the inclusive and dijet cross section of b-jets in pp collisions at $\sqrt{s}=7$ TeV with the ATLAS detector

We present a measurement of the inclusive and dijet differential cross sections of b-jets produced in proton--proton collisions at $\sqrt{s}=7$\,TeV, using data collected with the ATLAS detector that correspond to an integrated luminosity of 3\,pb$^{-1}$. Jets are reconstructed using the anti-$k_t$ algorithm with jet radius parameter $R=0.4$\,. The presence of a displaced vertex from the decay of long-lived hadrons is used to select a jet sample enriched in b-jets and the invariant mass of the charged particle tracks forming the vertex is fitted to extract the fraction of jets from b-quark production. The inclusive cross section is measured as a function of jet transverse momentum, in the range $20<\pt<260$\,GeV, and of rapidity, in the range $0<|y|<2.1$, where jets are fully contained in the tracking detectors of ATLAS. The dijet cross section is measured in the same rapidity range as a function of the dijet invariant mass, extending up to 670\,GeV. The resulting cross sections are compared with next-to-leading-order QCD predictions.