Drell-Yan Constraints on New Electroweak States: LHC as a $p p \to l^+ l^-$ Precision Machine

The Standard Model extensions with vector-like states which have either zero hypercharge or zero weak isospin are rather poorly constrained by the electroweak precision measurements. Such new states would however modify the running of the gauge couplings at high energies. As a result, the Drell-Yan process $p p \to l^+ l^-$ at the LHC places useful constraints on these models. The relevant observables include both the di-lepton invariant mass distribution $M_{l l}$ and the forward-backward asymmetry $A_{FB}$. We find that the LHC Run 1 data and the initial data from Run 2 surpass the sensitivity of LEP and already put meaningful constraints on the existence of such particles, which will become progressively stronger with more data.