Table 1.

Simulated background event samples used in this analysis with the corresponding generator, cross-section order in ${\mathit{\alpha }}_{\mathrm{s}}$ used to normalise the event yield, underlying-event tune and PDF set

Physics process	Generator	Parton shower	Cross section	Tune	PDF set
$Z/{\mathit{\gamma }}^{\ast }(\to \ell \ell )$ + jets	Sherpa 1.4.1	Sherpa 1.4.1	NNLO [29, 30]	Sherpa default	NLO CT10 [31]
$t\overline{t}$	Powheg-Box r2129	Pythia 6.426	NNLO + NNLL [32, 33]	Perugia2011C	NLO CT10
Single-top (Wt)	Powheg-Box r1556	Pythia 6.426	Approx. NNLO [34, 35]	Perugia2011C	NLO CT10
$t+Z$	MadGraph5 1.3.28	Pythia 6.426	LO	AUET2	CTEQ6L1 [36]
$t\overline{t}+W$ and $t\overline{t}+Z$	MadGraph5 1.3.28	Pythia 6.426	NLO [37, 38]	AUET2	CTEQ6L1
$t\overline{t}+WW$	MadGraph5 1.3.28	Pythia 8.165	LO	AUET2	CTEQ6L1
WW, WZ and ZZ	powheg-box r1508	Pythia 8.163	NLO [39, 40]	AUET2	NLO CT10