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During the last years ATLAS and CMS have reported a number of slight to milddiscrepancies in signatures of multileptons plus $b$-jets in analyses such as$t\bar t H$, $t\bar t W^\pm$, $t\bar t Z$ and $t\bar t t\bar t$. Among them, arecent ATLAS result on $t\bar t H$ production has also reported an excess inthe charge asymmetry in the same-sign dilepton channel with two or more$b$-tagged jets. Motivated by these tantalizing discrepancies, we study aphenomenological New Physics model consisting of a $Z'$ boson that couples toup-type quarks via right-handed currents: $t_R\gamma^\mu \bar t_R$,$t_R\gamma^\mu \bar c_R$, and $t_R \gamma^\mu \bar u_R$. The latter vertexallows to translate the charge asymmetry at the LHC initial state protons to afinal state with top quarks which, decaying to a positive lepton and a $b$-jet,provides a crucial contribution to some of the observed discrepancies. Throughan analysis at a detector level, we select the region in parameter space of ourmodel that best reproduces the data in the aforementioned $t\bar t H$ study,and in a recent ATLAS $t\bar t t \bar t$ search. We find that our modelprovides a better fit to the experimental data than the Standard Model for aNew Physics scale of approximately $\sim$500 GeV, and with a hierarchicalcoupling of the $Z'$ boson that favours the top quark and the presence of FCNCcurrents. In order to estimate the LHC sensitivity to this signal, we design abroadband search featuring many kinematic regions with differentsignal-to-background ratio, and perform a global analysis. We also definesignal-enhanced regions and study observables that could further distinguishsignal from background. We find that the region in parameter space of our modelthat best fits the analysed data could be probed with a significance exceeding3 standard deviations with just the full Run-2 dataset.

Topping-up multilepton plus b-jets anomalies at the LHC with a $Z'$ boson