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

Abstract

Abstract 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 $$ {m}_{Z^{\prime }} $$ m Z ′ and small gauge coupling gBL 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 mϕ< 2$$ {m}_{Z^{\prime }} $$ 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 mϕ> 2$$ {m}_{Z^{\prime }} $$ 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 gBL.