Abstract
FASER, the ForwArd Search ExpeRiment, is a currently operating experiment at the Large Hadron Collider (LHC) that can detect light long-lived particles produced in the forward region of the LHC interacting point. In this paper, we study the prospect of detecting light CP-even and CP-odd scalars at FASER and FASER 2. Considering a model-independent framework describing the most general interactions between a CP-even or CP-odd scalar and SM particles using the notation of coupling modifiers in the effective Lagrangian, we develop the general formalism for the scalar production and decay. We then analyze the FASER and FASER 2 reaches of light scalars in the large tan β region of the Type-I two Higgs double model as a case study, in which light scalars with relatively long lifetime could be accommodated. In the two benchmark scenarios we considered, the light (pseudo)scalar decay length varies in (10−8, 105) meters. Both FASER and FASER 2 can probe a large part of the parameter space in the large tan β region up to 107, extending beyond the constraints of the other existing experiments.
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Acknowledgments
FK acknowledges support by the Deutsche Forschungsgemeinschaft under Germany’s Excellence Strategy - EXC 2121 Quantum Universe - 390833306. HS is supported by the International Postdoctoral Exchange Fellowship Program. SS is supported by the Department of Energy under Grant No. DE-FG02-13ER41976/DE-SC0009913. WS is supported by the Junior Foundation of Sun Yat-sen University and Shenzhen Science and Technology Program (Grant No. 202206193000001, 20220816094256002).
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Kling, F., Li, S., Song, H. et al. Light Scalars at FASER. J. High Energ. Phys. 2023, 1 (2023). https://doi.org/10.1007/JHEP08(2023)001
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DOI: https://doi.org/10.1007/JHEP08(2023)001