New Physics Searches via Beam Normal Spin Asymmetry in Bhabha Scattering

Abstract: We examine the sensitivity of the beam normal spin asymmetry in Bhabha scattering to beyond the Standard Model (BSM) mediators, in the context of the JLab polarized positron program. A key property of this observable is that the Standard Model contribution exhibits a zero crossing at a fixed scattering angle, providing a clean, effectively background-free point for these searches. We consider scalar, vector and axial-vector mediators and present projected bounds, finding scalar and vector scenarios allowing to extend their search ranges significantly beyond existing constraints.