A reappraisal of constraints on $Z'$ models from unitarity and direct searches at the LHC

Understand

In a truly model-independent approach, we reexamine a minimal extension of the Standard Model (SM) through the introduction of an additional $U(1)$ symmetry leading to a new neutral gauge boson ($Z'$), allowing its kinetic mixing with the hypercharge gauge boson.

• An SM neutral scalar is used to spontaneously break this extra symmetry leading to the mass of the $Z'$.
• Except for three right-handed neutrinos no other fermions are added.
• We use the current LHC Drell-Yan data to put model-independent constraints in the parameter space of three quantities, namely, $M_{Z'}$, the $Z$-$Z'$ mixing angle ($\alpha_z$) and the extra $U(1)$ effective gauge coupling ($g'_x$), which absorb all model dependence.