Probing general $U(1{)}^{\prime }$ models with non-universal lepton charges at FASER/FASER2, COHERENT and long-baseline oscillation experiments

Abstract

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

30 pages, 6 figures, 2 tables. Accepted for publication in JHEP