SciPost Phys. Proc. 17, 012 (2025) ·
published 23 July 2025
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Recent R&D work associated with upgrading the SuperKEKB $e^+e^-$ collider with polarized electron beams is presented. The Chiral Belle physics program enables a set of unique precision measurements using the Belle II detector. It includes a set of measurements of $\sin^2\theta_W$ via separate left-right asymmetry ($A_{LR}$) measurements in annihilations to pairs of electrons, muons, taus, charm and b-quarks that yield precisions matching or exceeding those of the current world averages from measurements at the $Z^0$-pole, but at 10GeV, thereby also probing the running of the couplings. Chiral Belle will also probe for new physics via the highest precision measurements of neutral current universality ratios and precision measurements of tau lepton properties, including the tau magnetic moment. After summarizing the physics goals, developments related to provision of the polarized source, the new components of the accelerator lattice that rotate the electron spin from transverse to longitudinal at the interaction point, and polarimetry of the electron beam will be reported.
