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

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 mZ′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {m}_{Z^{\\prime }} $$\\end{document} 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< 2mZ′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {m}_{Z^{\\prime }} $$\\end{document}, 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> 2mZ′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {m}_{Z^{\\prime }} $$\\end{document}, 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.