Anomalous couplings in the Higgs-strahlung process

TL;DR

This work analyzes how non-standard, dimension-6, CP-conserving, custodial-symmetric operators modify Higgs-strahlung in $e^+e^-$ collisions. It parameterizes new physics via $ZZH$ and $eeZH$ interactions and derives polar and azimuthal angular distributions for $e^+e^- \to ZH \to f\bar f$, highlighting the roles of $a_0,a_1,b_1,c_L,c_R$ and the functions $\alpha(s)^{L,R}$, $\beta(s)^{L,R}$ in the cross sections. The authors identify high-energy behavior where contact terms grow with energy and the $\mathcal{O}_{\varphi W}$/$\mathcal{O}_{\varphi B}$ pieces modify the energy scaling, and show that polarization and energy variation enable complete or near-complete extraction of the anomalous coefficients. The results provide a framework for probing new Higgs-sector interactions at future $e^+e^-$ colliders through detailed angular analyses.

Abstract

The angular distributions in the Higgs-strahlung process $e^+e^-\to HZ\to H\bar f f$ are uniquely determined in the Standard Model. We study how these predictions are modified if non-standard couplings are present in the $ZZH$ vertex, as well as lepton-boson contact terms. We restrict ourselves to the set of operators which are singlets under standard $SU_3\times SU_2\times U_1$ transformations, CP conserving, dimension 6, helicity conserving, and custodial $SU_2$ conserving.

Figures (3)

• Figure 1: Anomalous $ZZH$/$\gamma ZH$ couplings and $e^+e^-ZH$ contact terms in the Higgs-strahlung process.
• Figure 2: Polar and azimuthal angles in the Higgs-strahlung process. [The polar angle $\theta_*$ is defined in the $Z$ rest frame.]
• Figure 3: Coefficients of the angular distributions as a function of the beam energy. Parameters are described in the text; in particular, $\alpha_i=1$ has ben chosen in the effective Lagrangian Eq.(\ref{['L-eff']}). [The $L,R$ coefficients of the azimuthal distribution coincide for the special choice $\alpha_i = 1$.]