Speaker
Description
Upgrading the SuperKEKB e+e− collider with polarized electron beams is under consideration as it opens a new program of precision electroweak physics at the $\Upsilon(4S)$. This Chiral Belle physics program includes determining $\sin^2\theta_W$ via separate left-right asymmetry ($A_{LR}$) measurements in $e^+e^−$ annihilations to pairs of electrons, muons, taus, charm and b-quarks using the Belle II detector. The precision that can be obtained matches that of the LEP/SLC world average and enables the probing of neutral current couplings with unprecedented precision in a manner sensitive to their running. At SuperKEKB, the measurements of the individual neutral current vector coupling constants to b-quarks, c-quarks and muons in particular will be substantially more precise than current world averages and the current $3\sigma$ discrepancy between the SLC $A_{LR}$ measurements and LEP $A_{FB}^b$ measurements of $\sin^2\theta_W^{eff}$ can be addressed. It can also provide the highest precision measurements of neutral current universality ratios. In addition, having a polarized electron beam enables measurements of tau lepton properties, including the tau g-2, with unrivaled precision. This presentation will cover the physics motivation and status of the R&D necessary for the upgrades to achieve and measure the SuperKEKB e- beam polarization.
