Measurement of jets produced in top quark events using the $e\mu$ final state with 2 b-tagged jets in pp collisions at $\sqrt{s }= $ 8 TeV with the ATLAS detector

The transverse momentum (pT) and multiplicity of jets produced in top quark events are measured using 20.3 inverse femtobarns of pp collision data at a center-of-mass energy of 8 TeV. Jets are selected from top events requiring an opposite-charge $e\mu$ pair and two b-tagged jets in the final state. The data are corrected to obtain the particle-level fiducial cross section for additional jets with rank 1-4, where rank=1 is the leading additional jet. These distributions are used to obtain the extra jet multiplicity as a function of minimum jet pT threshold. The results are compared with several next to leading order Monte Carlo generators. The resulting measurements can be used to tune Monte Carlo QCD modelling and may also reduce associated modelling uncertainties for LHC top quark physics measurements.