We propose a direct measurement of the CKM element V td at the LHC. Taking profit of the imbalance between d andd quark content in the proton, we show that a non-zero V td induces a charge asymmetry in the tW associated production. The main backgrounds to this process, tt production, and tW associated production mediated by V tb , give charge symmetric contributions at leading order in QCD. Therefore, using specific kinematic features of the signal, we construct a charge asymmetry in the di-lepton final state which, due also to a reduction of systematic uncertainties in the asymmetry, is potentially sensitive to V td suppressed effects. In particular, using signal and background simulations up to detector level, we show that this new observable could improve the current direct upper bound on |V td | already with existing LHC data. We also project that |V td | values down to ∼ 10 times the Standard Model prediction could be probed in the high luminosity phase of the LHC.

We study the ttbb final state at the LHC as a probe of New Physics that couples mainly to third generation of quarks. We analyze New Physics simplified models with resonances of spin 0, 1 and 2. The sensitivity of the final states ttbb, tttt, bbbb and tt on each of these models is used to identify an important region in parameter space that is still not excluded and where ttbb is the most sensitive final state. We indicate possible experimental hints and discuss potential issues of observables that rely mainly in Montecarlo predictions. A new observable is proposed that, at the price of requiring more statistics, reduces the impact of Montecarlo predictions. We use preliminary 13 TeV results to give a raw estimate on the discovery reach and propose simple improvements on the observables.