Dark Photon from Light Scalar Boson Decays at FASER

FASER is one of the promising experiments which search for long-lived particles beyond the Standard Model. In this paper, we focus on dark photon associating with an additional U(1) gauge symmetry, and also a scalar boson breaking this U(1) gauge symmetry. We study the sensitivity to the dark photon originated from U(1)-breaking scalar decays. We find that a sizable number of dark photon signatures can be expected in wider parameter space than previous studies.
Comment: 12 pages, 3 figures; v2: typos corrected, discussions and references added; v3: added references, figures, and comments on the light scalar case, calculated event number by Monte Carlo simulations, version to be published in JHEP; v4: replaced right panels of figures 2 and 4