Low Q2 weak mixing angle measurements and rare Higgs decays

A weighted average weak mixing angle θ_W derived from relatively low Q² 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 Q² measurements of sin²θ_W(Q²) 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.