Probing general U(1)′ models with non-universal lepton charges at FASER/FASER2, COHERENT and long-baseline oscillation experiments

A bstract The general anomaly-free U(1)′ models allow non-universal lepton charges. We explore the sensitivities of FASER/FASER2, COHERENT and DUNE/T2HK precision experiments to the new gauge boson Z ′ and the new CP-even scalar ϕ . With non-universal lepton charges, distinctive reaches at FASER/FASER2 emerge in the regime of low m Z ′ and small gauge coupling g BL for different U(1)′ charge setups. The COHERENT experiment and the future long-baseline experiments DUNE/T2HK also provide complementary probes to the available parameter space. For m ϕ < 2 m Z ′ , the search for the scalar ϕ at FASER/FASER2 is sensitive to the mixing angle between the scalar singlet and the SM Higgs. In the case of m ϕ > 2 m Z ′ , the kinematically allowed decay ϕ → Z ′ Z ′ changes the lifetime and decay rates of the scalar ϕ . The sensitivity reach highly depends on the Z ′ mass and the gauge coupling g BL .