Search for lepton flavor violating decay at FASER

Abstract

FASER is one of the promising experiments which search for long-lived particles beyond the Standard Model. In this paper, we consider charged lepton flavor violation (CLFV) via a light and weakly interacting boson and discuss the detectability by FASER. We focus on four types of CLFV interactions, i.e., the scalar-, pseudoscalar-, vector-, and dipole-type interaction, and calculate the sensitivity of FASER to each CLFV interaction. We show that, with the setup of FASER2, a wide region of the parameter space can be explored. Particularly, it is found that FASER2 has a sensitivity to very small coupling regions in which the rare muon decays, such as μ → eγ, cannot place bounds, and that there is a possibility to detect CLFV decays of the new light bosons.

Dark photon from light scalar boson decays at FASER

“…Using a large number of the dark Higgs bosons produced by heavy meson decays through the scalar mixing with the SM Higgs boson, it was shown that the sensitivity to the dark photon parameters can be enlarged. The similar analyses have been studied for inelastic dark matter [19], lepton flavor violation [12], dark Higgs [13,20,21] in gauge L µ − L τ [22] and B − L models [23]. In these studies, only decay of the on-shell dark Higgs was considered.…”

“…In refs. [11][12][13][14], the dark photon production from the dark Higgs decay at the FASER and other experiments [15][16][17][18] was studied. Using a large number of the dark Higgs bosons produced by heavy meson decays through the scalar mixing with the SM Higgs boson, it was shown that the sensitivity to the dark photon parameters can be enlarged.…”