PT Journal AU ATLAS Collaboration (Aaboud, Mea Alvarez Piqueras, D Barranco Navarro, L Cabrera Urban, S Castillo Gimenez, V Cerda Alberich, L Costa, MJ Fernandez Martinez, P Ferrer, A Fiorini, L Fuster, J Garcia, C Garcia Navarro, JE Gonzalez de la Hoz, S Higon-Rodriguez, E Jimenez Pena, J King, M Lacasta, C Mamuzic, J Marti-Garcia, S Melini, D Mitsou, VA Pedraza Lopez, S Rodriguez Rodriguez, D Romero Adam, E Ros, E Salt, J Sanchez Martinez, V Soldevila, U Sanchez, J Valero, A Valls Ferrer, JA Vos, M TI Measurement of jet activity produced in top-quark events with an electron, a muon and two b-tagged jets in the final state in pp collisions root s=13TeV with the ATLAS detector SO European Physical Journal C JI Eur. Phys. J. C PY 2017 BP 220 EP 38pp VL 77 IS 4 DI 10.1140/epjc/s10052-017-4766-0 LA English AB Measurements of jet activity in top-quark pair events produced in proton-proton collisions are presented, using 3.2 fb of pp collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS experiment at the Large Hadron Collider. Events are chosen by requiring an opposite-charge pair and two b-tagged jets in the final state. The normalised differential cross-sections of top-quark pair production are presented as functions of additional-jet multiplicity and transverse momentum, . The fraction of signal events that do not contain additional jet activity in a given rapidity region, the gap fraction, is measured as a function of the threshold for additional jets, and is also presented for different invariant mass regions of the system. All measurements are corrected for detector effects and presented as particle-level distributions compared to predictions with different theoretical approaches for QCD radiation. While the kinematics of the jets from top-quark decays are described well, the generators show differing levels of agreement with the measurements of observables that depend on the production of additional jets. ER