Branching fraction for $Z$ decays to four leptons and constraints on new physics

Abstract

The LHC experiments have measured the branching fraction for $Z$ decays to four leptons (electrons or muons). We have combined these measurements with the result $\mathcal{B}(Z\to 4\ell )=(4.58\pm 0.26)\times 10^{-6}$, allowing a precise comparison to the standard model prediction of $(4.70\pm 0.03)\times 10^{-6}$. We use a minimal extension of the standard model to demonstrate that this combined value may be used to set stringent limits on new physics.

12 pages, 6 figures