Landau-Yang Theorem and Decays of a Z' Boson into Two Z Bosons

TL;DR

The decay of a Z' boson into two Z bosons is studied by extending the Landau-Yang theorem to a parent particle decaying into twoZ bosons by finding the two possible couplings are anomaly induced and CP violating.

Abstract

We study the decay of a Z' boson into two Z bosons by extending the Landau-Yang theorem to a parent particle decaying into two Z bosons. For a spin-1 parent the theorem predicts: 1) there are only two possible couplings and 2) the normalized differential cross-section depends on kinematics only through a phase shift in the azimuthal angle between the two decay planes of the Z boson. When the parent is a Z' the two possible couplings are anomaly-induced and CP-violating, respectively. At the Large Hadron Collider (LHC) effects of the two couplings could be disentangled when both Z bosons decay leptonically.

Figures (1)

• Figure 1: Two decay planes of $Z_1\to \ell_1\bar{\ell}_1$ and $Z_2\to \ell_2\bar{\ell}_2$ define the azimuthal angle $\phi\in[0,2\pi]$ which rotates $\ell_2$ to $\ell_1$ in the transverse view. The polar angles $\theta_1$ and $\theta_2$ shown are defined in the rest frame of $Z_1$ and $Z_2$, respectively.