Low Q^2 Weak Mixing Angle Measurements and Rare Higgs Decays

TL;DR

This paper explores a potential new dark Z boson explaining a discrepancy in weak mixing angle measurements, analyzing constraints from electroweak data and rare Higgs decay searches, and discusses future experimental sensitivities.

Contribution

It introduces a model of a dark Z boson to explain the weak mixing angle discrepancy and evaluates constraints and future detection prospects.

Findings

Approximate 1.8 sigma discrepancy in weak mixing angle measurements.

Constraints from electroweak precision tests and LHC Higgs decay searches.

Potential signals in low energy parity violation and rare Higgs decays.

Abstract

A weighted average weak mixing angle theta_W derived from relatively low Q^2 experiments is compared with the Standard Model prediction obtained from precision measurements. The approximate 1.8 sigma discrepancy is fit with an intermediate mass (~ 10-35 GeV) "dark" Z boson Z_d, corresponding to a U(1)_d gauge symmetry of hidden dark matter, which couples to our world via kinetic and Z-Z_d mass mixing. Constraints on such a scenario are obtained from precision electroweak bounds and searches for the rare Higgs decays H -> Z Z_d -> 4 charged leptons at the LHC. The sensitivity of future anticipated low Q^2 measurements of sin^2 theta_W(Q^2) to intermediate mass Z_d is also illustrated. This dark Z scenario can provide interesting concomitant signals in low energy parity violating measurements and rare Higgs decays at the LHC, over the next few years.