  We study the $t\bar t b \bar b$ 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 $t\bar t b\bar b$, $t\bar t t \bar t$, $b \bar b b \bar b$
and $t \bar t$ on each of these models is used to identify an important region
in parameter space that is still not excluded and where $t\bar t b \bar b$ 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.
