Electron Beam Polarimetry using Atomic Hydrogen Møller Polarimeter for P2 experiment

P2 experiment at the upcoming MESA accelerator in Mainz aims for a high precision determination of the weak mixing angle sin²θ_W to a precision of 0.13% at a four-momentum transfer of Q² = 4.5 × 10⁻³ GeV² to provide a sensitive test of the standard model up to a mass scale of 50 TeV, extendable to 70 TeV. The experiment will be conducted at 155 MeV due to small γZ-box contributions. The size of the asymmetry at the proposed at 155 MeV electron beam energy will be the smallest asymmetry ever measured in electron scattering requiring high precision electron beam polarimetry. An atomic Hydrogen trap polarimeter, “Hydro-Møller” utilizing Møller scattering will provide online beam polarization measurements for the P2 experiment. The “Hydro-Møller” polarimeter will replace conventional ferromagnetic target with a trapped polarized hydrogen atomic target located inside an 8 T solenoid with a magnetic field pointing along the beam direction. The target will generate high purity electronic spin ensemble that will give the main advantage with respect to existing Møller polarimeters. The current status and future plans for Hydro-Møller polarimeter development will be provided.