Jet multiplicity distributions in top quark pair ($t\bar{t}$) events are measured in $pp$ collisions at a centre-of-mass energy of 8\;\text{TeV} with the CMS detector at the LHC, using a data set corresponding to an integrated luminosity of 19.7/fb. The measurement is performed in the dilepton decay channels $e^+e^-$, $\mu^+\mu^-$, and $e^\pm\mu^\mp$). The absolute and normalized differential cross-sections for $t\bar{t}$ production are measured as a function of jet multiplicity for different jet transverse momentum thresholds and the kinematic properties of the leading additional jets. The differential $t\bar{t}b$ and $t\bar{t}b\bar{b}$ cross-sections are presented for the first time as a function of the kinematic properties of the leading additional $b$-jets. Furthermore, the fraction of events without additional jets above a threshold is measured as a function of the transverse momenta of the leading additional jets and the scalar sum of the transverse momenta of all additional jets.
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